Insight into tuning of ZrO2 distribution and mechanical properties of directionally solidified Al2O3/(5Re0.2)AG/ZrO2 eutectic ceramic composites

Insight into tuning of ZrO2 distribution and mechanical properties of directionally solidified Al2O3/(5Re0.2)AG/ZrO2 eutectic ceramic composites | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Insight into tuning of ZrO2 distribution and mechanical properties of directionally solidified Al2O3/(5Re0.2)AG/ZrO2 eutectic ceramic composites Yujie Zhong, Zhe Li, Xu Wang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3137798/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract A novel Al 2 O 3 /(Y 0.2 Er 0.2 Yb 0.2 Ho 0.2 Lu 0.2 ) 3 Al 5 O 12 ((5Re 0.2 )AG)/ZrO 2 eutectic high entropy oxide ceramic composites (HEOCs) was prepared by the directional solidification technique. The Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs had a refined microstructure and different crystallographic orientation relationships of Al 2 O 3 || (5Re 0.2 )AG || ZrO 2 , {11–20}Al 2 O 3 || {100}(5Re 0.2 )AG || {100}ZrO 2 , {0001} Al 2 O 3 || {103}(5Re 0.2 )AG || {100}ZrO 2 compared to Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites. ZrO 2 in the Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs was distributed more uniformly and dispersedly than in Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites due to the similar volume strain of Al 2 O 3 /(5Re 0.2 )AG, (5Re 0.2 )AG/ZrO 2 and Al 2 O 3 /ZrO 2 . As a result, mechanical performance including hardness, elastic modulus, and fracture toughness had been greatly improved because of the refined microstructure, tailored interfacial structure, and homogeneous distribution of ZrO 2 caused by the introduction of the high entropy (5Re 0.2 )AG. directional solidification high-entropy oxide ceramic composites eutectics orientation relationship interfacial structure Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1. Introduction High-performance aero-engines put forward higher requirements on the temperature-bearing capacity of turbine blade materials. For example, the turbine inlet temperature of an engine with a thrust-to-weight ratio of 10 or more is up to 1600 o C-1650 o C [ 1 ]. Directionally solidified Al 2 O 3 -based eutectic ceramic composites with high melting point (~ 1800 o C), outstanding high-temperature creep and oxidation resistance are considered to be one of the next generation of ultra-high temperature structural materials [ 2 , 3 ]. Previous studies have shown that if they can be applied as a guide vane or combustion chamber liner, it could significantly improve the thrust-to-weight ratio of an engine and thermal efficiency will also increase by 9% [ 4 ]. However, the poor fracture toughness and high-temperature strength limit their application as a high-temperature structural material. Several classes of Al 2 O 3 -based directionally solidified ceramic composites have been widely studied, such as binary eutectics Al 2 O 3 /Y 3 Al 5 O 12 [ 5 , 6 ], Al 2 O 3 /Ed 3 Al 5 O 12 [ 7 , 8 ], Al 2 O 3 /GdAlO 3 [ 9 – 11 ], Al 2 O 3 /SmAlO 3 [ 12 , 13 ] and ternary eutectics Al 2 O 3 /Y 3 Al 5 O 12 (YAG)/ZrO 2 [ 14 , 15 ], Al 2 O 3 /Ed 3 Al 5 O 12 /ZrO 2 [ 16 ]. In general, the fracture toughness of ternary eutectics is higher than that of binary eutectics due to the addition of ZrO 2 [ 17 – 21 ]. The introduction of ZrO 2 makes the ternary eutectic layer finer than the binary eutectic layer under the same solidification process, which improves its bending strength [ 22 ]. The crack kinked [ 20 , 23 ], deflected [ 23 ] at ZrO 2 , or even was prevented by ZrO 2 [ 24 ]. ZrO 2 acts as the toughening phase, and its morphology, size and distribution play a decisive role in the toughening effect. However, according to the morphology of directionally solidified Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites reported in literature [ 15 , 20 , 25 – 30 ], it is found that ZrO 2 was mainly distributed between Al 2 O 3 and YAG in the form of fine round rods or lamellae, and a small amount located in Al 2 O 3 , and a very small amount in YAG. It evidently shows that the morphology and distribution of ZrO 2 are not random, but are governed by certain laws. Our previous work found that the distribution of ZrO 2 was mainly dominated by the minimization of the interfacial strain energy. In directionally solidified Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites, the mismatch strain of Al 2 O 3 -YAG, Al 2 O 3 -ZrO 2 , and YAG-ZrO 2 is -0.9%, -0.1% and 0.2%, respectively [ 15 ], which imply that the interfacial strain energy of Al 2 O 3 -YAG is much higher than that of YAG-ZrO 2 and Al 2 O 3 -ZrO 2 . To minimize the total interfacial strain energy of the eutectic system, ZrO 2 diffuses and distributes between Al 2 O 3 and YAG with the largest possible surface area (i.e., rod or lamellar) to reduce the interface area formed by YAG and Al 2 O 3 phase, which has the largest interfacial strain energy. This heterogeneous distribution of ZrO 2 weakens its strengthening and toughening effect. It is expected that ZrO 2 can be homogeneously distributed in Al 2 O 3 , YAG, and between the two, to achieve the best strengthening and toughening effect. Therefore, the authors envision if the distribution of ZrO 2 could be modified by tuning the interfacial mismatch. The solid solution will lead to lattice distortion, which becomes more severe as the number of solid solution elements increases [ 31 ]. Lattice distortion is bound to cause changes in the d -spacing. Therefore, the solid solution seems to be an effective way to tailor the interfacial mismatch. Recently, high-entropy ceramic composites, which are commonly referred to as a solid solution formed by four or more ceramic components, have shown unexpected properties such as high hardness, superior elastic modulus as well as high fracture toughness [ 32 ]. For example, the fracture toughness of (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )(C 0.5 N 0.5 ) is 8.4 MPa·m 1/2 , much higher than that of binary ceramic composites [ 33 ]. The fracture toughness of (Zr 0.25 Nb 0.25 Ti 0.25 V 0.25 )C is up to 4.7 ± 0.5 MPa·m 1/2 , larger than that of the individual component [ 32 ]. The above studies suggest that in addition to raising the performance of high-entropy ceramic composites, the solid solution may also tune the interfacial structure formed by the high-entropy with other phases through lattice distortion, thereby further optimizing the mechanical properties. In the present work, the YAG phase in Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites is replaced by an oxide solid solution (Y 0.2 Er 0.2 Yb 0.2 Ho 0.2 Lu 0.2 ) 3 Al 5 O 12 , and directionally solidified Al 2 O 3 /(Y 0.2 Er 0.2 Yb 0.2 Ho 0.2 Lu 0.2 ) 3 Al 5 O 12 ((5Re 0.2 )AG)/ZrO 2 ternary eutectic high entropy oxide ceramic composites (HEOCs) is prepared with an optical floating zone furnace. The as-prepared eutectic HEOCs are composed of Al 2 O 3 , the (5Re 0.2 )AG, and ZrO 2 single-crystal phases. The effect of the lattice distortion of (5Re 0.2 )AG on the distribution of ZrO 2 and interfacial structure is reported for the first time. Mechanical properties including nano/Vickers hardness, elastic modulus, and fracture toughness of Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs are studied and compared with those of Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites. These results may cast light for optimizing the mechanical properties of Al 2 O 3 -based eutectic ceramic composites. 2. Experimental section 2.1 Preparation of samples and direction solidification Commercially available ceramic powders of Re 2 O 3 (Re = Y, Lu, Ho, Er and Yb, 99.99% purity), ZrO 2 (99.99% purity), and Al 2 O 3 (99.95% purity) were used to prepare the Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs. Al 2 O 3 , Re 2 O 3 and ZrO 2 powders were mixed with a molar ratio of 65:16:19 according to the eutectic point in the ternary phase diagram [ 34 , 35 ]. Re 2 O 3 powders were mixed in equal molar fractions. Then the prepared powder was wet ball milled with alcohol for 12 h to ensure homogeneity. The slurry was dried and sieved through a 120-mesh net to obtain the requested powders. Precursors were prepared by holding at 45 MPa for 5 minutes in a stainless-steel mold with a dimension of 10 × 10 × 100 mm 3 and then sintering without pressure in a muffle furnace at 1823 K for 2.5 h. The directional solidification process was carried out in an optical floating zone (OFZ) furnace with a slight overpressure (~ 1.1 bars) in an argon atmosphere. During the preparation process, precursors were melted using four 3 kW xenon arc lamps with a withdrawal rate of 20 mm/h. The prepared crystals measured up to 120 mm in length and about 10 mm in diameter. 2.2 Microstructure characterization The as-prepared Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOC bars and Al 2 O 3 /YAG/ZrO 2 eutectic bars were sliced by wire-cutting equipment. Samples were well grounded with 600#, 1000# diamond discs, and SiC paper up to 2000#. They were further polished using 2.5 µm diamond paste. TEM samples were prepared using a dual-beam focused ion beam (FIB, Thermo Scientific Scios 2, USA). The phase composition was analyzed employing an X-ray diffractometer (LabX XRD-6000, Japan). The microstructure was characterized using scanning electron microscopy (SEM, JSM-6700 F, JEOL, Japan). Orientation relationships were determined with electron-back scattered diffraction (EBSD, NordlysNano, Oxfordshire, UK). A 300 kV transmission electron microscopy (TEM, FEI Talos F300C, U) equipped with an energy dispersive X-ray spectroscopy (EDS) analysis unit was used for high-resolution transmission electron microscopy (HRTEM) observation and EDS elemental analysis. 2.3 Mechanical properties testing The Vickers hardness was obtained using a Vickers Indenter (HVS-10AT, China) when loaded at 2.94, 4.9, 9.8, 19.6, 29.4, and 49 N. The holding time is 15 s. In addition, the fracture toughness ( K IC ) was measured on the basis of the indentation method using the following equation[ 36 ]: K IC = 0.016 × (E/H V ) 1/2 p/c 3/2 (1) where E is Young's modulus, H V is the Vickers hardness, c is the half-length indentation diagonal and p is the indentation load. Nanoindentation tests were performed on well-polished sample surfaces employing a Nano-Indenter G200 (KLA, USA) system equipped with a diamond Berkovich indenter with a 20 nm tip radius to evaluate their nanohardness and elastic modulus. The maximum load for nanoindentation mapping was 29 mN and the indentation spacing was 10 µm. 3. Results 3.1 Microstructure of the Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 ternary eutectic HEOCs The composition of the Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs was investigated by the XRD technique and compared with Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites, as depicted in Fig. 1 . In comparison with standard PDF cards, the Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs consist of three phases: Al 2 O 3 , the (5Re 0.2 )AG and cubic ZrO 2 (c-ZrO 2 ). Taking a careful observation of the magnified regions b and c, it is found that neither the (1 0 4) peak position of Al 2 O 3 nor the (2 0 0) peak position of ZrO 2 shifts, while the (4 2 0) peak position of the (5Re 0.2 )AG shifts towards the high angle in contrast to Al 2 O 3 /Y 3 A 5 O 12 /ZrO 2 eutectic ceramic composites. The shift is more pronounced at the high-angle peak position, which means a reduction of d -spacing of the (5Re 0.2 )AG phase according to the Bragg equation. The transverse microstructures of Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs and Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites are displayed in Fig. 2 . Both of the eutectics have a so-called Chinese-script microstructure. The dark area is Al 2 O 3 phase, the grey area is the (5Re 0.2 )AG or YAG phase and the white area is ZrO 2 phase. Comparing Figs. 2 a and c at the same magnification, it is found that the microstructure size of Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs is finer and more diffuse under the same solidification process. It is about 1/2 to 1/3 of that of Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites. Especially for ZrO 2 phase, comparing Figs. 2 b and d, the size of ZrO 2 tissue in Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs is about 1/4 to 1/3 of that in Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites. In addition, the morphology and distribution of ZrO 2 in the two eutectics are also different. In Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites, ZrO 2 is mainly distributed at the interface between Al 2 O 3 and YAG in the form of thin laminate and round rod-like shape, as reported previously [ 15 ]. However, in the Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs, ZrO 2 is rather well-distributed both in the Al 2 O 3 , (5Re 0.2 )AG and their interface with a tiny round rod-like shape. The microstructure of Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs was further observed by TEM, as shown in Fig. 3 a. It can be seen that the three phases are well-boned by interfaces, which are clean and smooth, with no intermediate phase or amorphous phase. According to the different electron diffraction patterns, the white is Al 2 O 3 , the light gray is the (5Re 0.2 )AG, and the dark gray is c-ZrO 2 . XRD results signify that there is a change in the d -spacing of the (5Re 0.2 )AG compared to the YAG. To verify the XRD result, the d -spacings of both (0 2 0) planes of two were carefully measured based on the electron diffraction patterns, as marked in HRTEM maps (Figs. 3 b and c). The d -spacing of (5Re 0.2 )AG (0 2 0) plane is 0.5894 nm, smaller than that of the YAG (0 2 0) plane (0.6004 nm). To check our measurement results, the d -spacing of (5Re 0.2 )AG (3 0–1) was measured and compared with that of (3 0 1) calculated by measured (0 2 0). The two values were found to be consistent. The results indicate that the (5Re 0.2 )AG lattice is negatively distorted compared with YAG, which agrees well with the XRD results. Scanning transmission electron microscopy (STEM) is employed for the investigation of element distribution of the as-grown Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs, as presented in Fig. 4 . According to the EDS line scan results shown in Fig. 4 b, five cations (i.e., Y 3+ , Er 3+ , Ho 3+ , Lu 3+ and Yb 3+ ) have almost the same composition of ~ 20% as expected. Some of the Y, Yb, Er, Ho, Lu and Al elements are solved into the ZrO 2 phase, which play a role in stabilizing its cubic crystal structure. Figures 4 c-g show a highly homogenous distribution of Y, Er, Yb, Ho, and Lu elements in the (5Re 0.2 )AG phase, indicating that the Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs are well fabricated. 3.2 Orientation relationships the interfaces The orientation relationships of the Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs are examined by EBSD, and the result is presented in Fig. 5 . Figures 5 b-d show the preferred growth direction of the three phases, respectively, for Al 2 O 3 (the two colors mean the same direction of [ 17 ]), for the (5Re 0.2 )AG, and for ZrO 2 . At first glance, Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs has the same preferred growth directions as Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites reported in the literature [ 37 ]. However, further analysis of the inverse polar figure (lower left corner in Fig. 5 c) demonstrates that the preferred growth direction of (5Re 0.2 )AG is , exactly. Therefore, the preferred growth directions are: Al 2 O 3 || (5Re 0.2 )AG || ZrO 2 . Figure 6 exhibits the pole figures of Al 2 O 3 , the (5Re 0.2 )AG, and ZrO 2 shown in Fig. 5 . It can be obtained that the orientation relationships of the Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs are: {11–20} Al 2 O 3 || {100} (5Re 0.2 )AG || {100} ZrO 2 , and {0001} Al 2 O 3 || {103} (5Re 0.2 )AG || {100} ZrO 2 , as circled by the red circles and black circles in Figs. 6 a, b and c, respectively. In general, the orientation relationships of the three eutectic phases are summarized as follows: Al 2 O 3 || (5Re 0.2 )AG || ZrO 2 (white circles), {11–20} Al 2 O 3 || {100} (5Re 0.2 )AG || {100} ZrO 2 (black circles), {0001} Al 2 O 3 || {103} (5Re 0.2 )AG || {100} ZrO 2 (red circles). Notably, the orientation relationships of directionally solidified Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs are different from that of Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites [ 37 ]. To further investigate the orientation relationship interfacial structure of the Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs, thin-foil samples were prepared for the HRTEM tests. Figures 7 a, d and g show the HRTEM images of the three interfaces marked by the red squares in Fig. 3 . Interface I is Al 2 O 3 /ZrO 2 , interface II is ZrO 2 /(5Re 0.2 )AG and interface III is Al 2 O 3 /(5Re 0.2 )AG. It can be seen that all three interfaces are clean and well-oriented. From the corresponding selected-area diffraction patterns of the interfaces, depicted in Figs. 7 b, e and h, the orientation relationship of the three interfaces are: Interface I: [1-100] (11–20) Al 2 O 3 || [100] (020) ZrO 2 , Interface II: [100] (020) ZrO 2 || [103] (040) (5Re 0.2 )AG, Interface III: [1-100] (11–20) Al 2 O 3 || [103] (040) (5Re 0.2 )AG, which are the same as that obtained from the EBSD experiments. These well-oriented interfaces are semi-coherent, as shown in Figs. 7 c, f and i. The lattice misfit is accommodated by a series of periodic misfit dislocations. The periods of the misfit dislocation in sequence are 1/13 for Al 2 O 3 /ZrO 2 , 1/7 for ZrO 2 /(5Re 0.2 )AG and 1/5 for Al 2 O 3 /(5Re 0.2 )AG. 3.3 Mechanical properties To compare and study the influence of (5Re 0.2 )AG instead of YAG, mechanical properties including nanohardness, Vickers hardness, elastic modulus, and fracture toughness of Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs and Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites prepared by the same process were studied at the same time. Figure 8 shows the Vickers hardness of Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs and Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites under different applied loads. It can be found that the microhardness of both samples decreases with the increasing load. This may be due to the porosity in the ceramic composites. However, the Vickers hardness of Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs is higher than that of Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites. At a load of 9.8 N, the Vickers hardness of Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs is about 19.7 ± 0.4 GPa and that of Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites is about 16.9 ± 0.57 GPa. The nanoindentation method was used to test the nanohardness and elastic modulus of the two samples, as summarized in Table I. The nanohardness of Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs is 33.17 ± 0.52 GPa, higher than 21.66 ± 0.43 GPa of Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites. The elastic modulus is 436.1 ± 6.7 GPa, while that of Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites is 357.8 ± 8.9 GPa. It is worth mentioning that the elastic modulus is not only higher than that of Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites but also higher than that of their component. The fracture toughness is estimated based on the indentation method with a load of 49 N. The fracture toughness is calculated to be 8.55 ± 0.36 MPa/m 1/2 , almost 2.5 times that of Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites (3.54 ± 0.34 MPa/m 1/2 ). Table I. The measured nanohardness, elastic modulus, and fracture toughness of Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs and Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites prepared with the same solidification process. Samples Nanohardness (GPa) Elastic modulus (GPa) Fracture toughness (K IC , MPa/m 1/2 ) Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 33.17 ± 0.52 436.1 ± 6.7 8.55 ± 0.36 Al 2 O 3 /YAG/ZrO 2 21.66 ± 0.43 357.8 ± 8.9 3.54 ± 0.34 4. Discussion 4.1 Distribution of ZrO 2 Figure 9 illustrates the combined orientation relationships between Al 2 O 3 , the (5Re 0.2 )AG and ZrO 2 obtained from the above experimental results, together with that of Al 2 O 3 /YAG/ZrO 2 of our previous work [ 15 ] for comparison. The difference was marked with a pink dashed rectangle. It can be seen qualitatively that the mismatch between (0003)Al 2 O 3 and (30 − 1)(5Re 0.2 )AG in Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs is significantly smaller than that between (0003)Al 2 O 3 and (004)YAG in Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites. That is to say, the mismatch difference between Al 2 O 3 /ZrO 2 and (5Re 0.2 )AG/ZrO 2 in Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs is small, but that between Al 2 O 3 /ZrO 2 and YAG/ZrO 2 in Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites is relatively large. Therefore, ZrO 2 in Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs can be distributed in both Al 2 O 3 , (5Re 0.2 )AG, and between them, making ZrO 2 homogenously dispersed without segregation. According to the measured d -spacing in Figs. 3 b and c, the lattice constant of the (5Re 0.2 )AG phase is calculated to be 1.1788 nm, smaller than 1.2008 nm of the YAG phase. It can be inferred that the lattice distortion leads to a change in the crystal orientation relationship, as clearly illustrated in Fig. 10 . Comparing Figs. 10 a and b, the preferred growth direction of (5Re 0.2 )AG changes to be [103] and the parallel plane changes to be {-301}. However, the orientation relationship of Al 2 O 3 and ZrO 2 remains unchanged. To quantitatively investigate the effect of the change of Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs orientation relationship on the interfacial strain, the 3D lattice matching of the interfaces is investigated by the near-coincident site lattice (NCSL) theory. Al 2 O 3 is a rhombohedral structure with a = 0.47544 nm and c = 1.29725 nm. The (5Re 0.2 )AG is a cubic structure, with a = 1.1788 nm. And ZrO 2 is a cubic structure with a = 0.51523 nm. All lattice constants are derived from the average of multiple measurements of the d -spacings in HRTEM. In the NCSL analysis, a typically used tolerance factor of 0.05 nm is applied to define 'near-coincident sites' [ 38 ]. The projections of the Al 2 O 3 , ZrO 2 and (5Re 0.2 )AG lattices along the parallel axes of [ 10 – 10 ] Al 2 O 3 || [100] ZrO 2 , [103] (5Re 0.2 )AG || [100] ZrO 2 and [ 10 – 10 ] Al 2 O 3 || [103] (5Re 0.2 )AG, are displayed in Figs. 11 a, b and c, respectively. The so-called smallest NCSL models along the parallel axes are formed by vectors, as listed in Table II. Table II. The smallest NCSL model of Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs formed by vectors along the parallel axes. [ 10 – 10 ] Al 2 O 3 || [100] ZrO 2 [103] (5Re 0.2 )AG || [100] ZrO 2 [ 10 – 10 ] Al 2 O 3 || [103] (5Re 0.2 )AG u 1 = 4[001]ZrO 2 ≈ 5[ 10 – 10 ]Al 2 O 3 u 1 '=5[001]ZrO 2 ≈ 7[103](5Re 0.2 )AG u 1 "=11[103](5Re 0.2 )AG ≈ 10[ 10 – 10 ]Al 2 O 3 u 2 = 5[100]ZrO 2 ≈ 6[0003]Al 2 O 3 u 2 '=5[100]ZrO 2 ≈ 7[30 − 1](5Re 0.2 )AG u 2 "=7[30 − 1](5Re 0.2 )AG ≈ 6[0003]Al 2 O 3 u 3 = 6[010]ZrO 2 ≈ 13[1-210]Al 2 O 3 u 3 '=7[010]ZrO 2 ≈ 12[040](5Re 0.2 )AG u 3 "=4[040](5Re 0.2 )AG ≈ 5[1-210] Al 2 O 3 The volumetric strain between the NCSL models referred to each lattice can be calculated by [ 40 ] $$\begin{array}{c} {\epsilon }_{{v}_{{Al}_{2}{O}_{3}-Zr{O}_{2}}}= \frac{{V}_{NCSL-{Al}_{2}{O}_{3}}-{V}_{NCSL-Zr{O}_{2}}}{{(V}_{NCSL-{Al}_{2}{O}_{3}}+{V}_{NCSL-Zr{O}_{2}})/2}\#\left(2\right)\end{array}$$ $$\begin{array}{c}{\epsilon }_{{v}_{{Al}_{2}{O}_{3}-\left(5{Re}_{0.2}\right)AG}}= \frac{{V}_{NCSL-{Al}_{2}{O}_{3}}-{V}_{NCSL-\left(5{Re}_{0.2}\right)AG}}{{(V}_{NCSL-{Al}_{2}{O}_{3}}+{V}_{NCSL-\left(5{Re}_{0.2}\right)AG})/2}\#\left(3\right)\end{array}$$ $$\begin{array}{c}{\epsilon }_{{v}_{{ZrO}_{2}-\left(5{Re}_{0.2}\right)AG}}= \frac{{{V}_{NCSL-Zr{O}_{2}}-V}_{NCSL-\left(5{Re}_{0.2}\right)AG}}{{(V}_{NCSL-\left(5{Re}_{0.2}\right)AG}+{V}_{NCSL-Zr{O}_{2}})/2}\#\left(4\right)\end{array}$$ where \({V}_{NCSL-{Al}_{2}{O}_{3}}\) , \({V}_{NCSL-Zr{O}_{2}}\) and \({V}_{NCSL-\left(5{Re}_{0.2}\right)AG}\) are volumes of the NCSL unit cells of the Al 2 O 3 , ZrO 2 and (5Re 0.2 )AG lattices, respectively. The volumetric strain is computed to be 0.576% for \({\epsilon }_{{v}_{{Al}_{2}{O}_{3}-Zr{O}_{2}}}\) , 0.668% for \({\epsilon }_{{v}_{{Al}_{2}{O}_{3}-\left(5{Re}_{0.2}\right)AG}}\) and − 0.604% for \({\epsilon }_{{v}_{{ZrO}_{2}-\left(5{Re}_{0.2}\right)AG}}\) . Calculations indicate that the volume strains of the three phases are almost identical, implying the almost same interfacial strain energy. For comparison, the smallest NCSL model of the Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites along the parallel axes is also formed by vectors, as detailed in Table III. Moreover, the volume strain is calculated to be 0.576% for \({\epsilon }_{{v}_{{Al}_{2}{O}_{3}-Zr{O}_{2}}}\) , -2.3% for \({\epsilon }_{{v}_{{Al}_{2}{O}_{3}-YAG}}\) , and 0.295% for \({\epsilon }_{{v}_{{ZrO}_{2}-YAG}}\) . Apparently, the value of \({\epsilon }_{{v}_{{Al}_{2}{O}_{3}-YAG}}\) is an order of magnitude greater than the other two. The results verified the results previously reported in the literature [ 15 ]. According to the principle of minimizing the interfacial strain energy of the system, ZrO 2 tends to distribute between Al 2 O 3 and YAG, so as to suppress the formation of the Al 2 O 3 /YAG interface having high interfacial strain. However, the volume strain differences of the three interfaces in Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs are very small, making ZrO 2 phase uniformly distributed in Al 2 O 3 , the (5Re 0.2 )AG, and between them. Table III. The smallest NCSL model of Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites formed by vectors along the parallel axes. [ 10 – 10 ] Al 2 O 3 || [100] ZrO 2 [100] YAG || [100] ZrO 2 [ 10 – 10 ] Al 2 O 3 || [100] YAG u 1 = 4[001]ZrO 2 ≈ 5[ 10 – 10 ]Al 2 O 3 u 1 '=7[001]ZrO 2 ≈ 12[004]YAG u 1 "=4[004]YAG ≈ 3[ 10 – 10 ]Al 2 O 3 u 2 = 5[100]ZrO 2 ≈ 6[0003]Al 2 O 3 u 2 '=7[100]ZrO 2 ≈ 12[400]YAG u 2 "=3[400]YAG ≈ 2[0003]Al 2 O 3 u 3 = 12[020]ZrO 2 ≈ 13[1-210]Al 2 O 3 u 3 '=7[020]ZrO 2 ≈ 6[040]YAG u 3 "=4[040]YAG ≈ 5[1-210] Al 2 O 3 4.2 Effect of microstructure on mechanical performance It is obvious that the mechanical properties of Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs are better than Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites. The reasons are generally attributed to (i) the substitution of YAG with (5Re 0.2 )AG, (ii) tailored interfacial structure, and (iii) the homogeneous distribution of ZrO 2 . As shown in Fig. 2 , the eutectic microstructure of directionally solidified Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs is much finer compared to Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites prepared with the same preparation process. This can be attributed to the 'hysteresis diffusion' effect of high-entropy materials [ 39 ]. During the liquid-solid transition, the atoms of each group diffuse corporately from a chaotic state to an ordered state. There are more atoms in the Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs, leading to a relatively low diffusion rate and thus inhibiting the growth of the lamellae. Therefore, compared with Al 2 O 3 /YAG/ZrO 2 , the interfacial area per unit area is more in Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs. The increase of planar defects will undoubtedly increase its hardness. Furthermore, as demonstrated by the XRD and TEM results, due to the reduced lattice constant ( r 0 ) of (5Re 0.2 )AG compared to YAG, the lattice energy of (5Re 0.2 )AG becomes higher according to the Born–Landé equation [ 40 ]: $$\begin{array}{c}{E}_{n}=-\frac{{N}_{A}M{z}^{+}{z}^{-}{e}^{2}}{4\pi {\epsilon }_{0}{r}_{0}}\left(1-\frac{1}{n}\right) \#\left(5\right)\end{array}$$ where N A is Avogadro constant, M is Madelung constant, z +/− is cationic/anion charge, ε 0 is vacuum permittivity (a constant), n is Born index (= 5 ~ 12), and r 0 is the distance between the nearest two ions. Therefore, the higher lattice bonding energy leads to higher hardness and elastic modulus of (5Re 0.2 )AG. This is another pronounced reason for the improved hardness and elastic modulus of Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs. In addition, since the introduction of the (5Re 0.2 )AG, the interfacial structures are tailored, making ZrO 2 distribute finer and more dispersed. Fine ZrO 2 is distributed in both Al 2 O 3 and (5Re 0.2 )AG, as well as between Al 2 O 3 and (5Re 0.2 )AG, improving the fracture toughness of Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs. 5. Conclusion In summary, Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs were successfully prepared by the directional solidification method. The ceramic was composed of Al 2 O 3 , the (5Re 0.2 )AG and ZrO 2 phases. There was a lattice distortion in the (5Re 0.2 )AG phase. The orientation relationship of the Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs was determined to be [1-100] Al 2 O 3 || [100] ZrO 2 || [103] (5Re 0.2 )AG, (11–20) Al 2 O 3 || (020) ZrO 2 || (040) (5Re 0.2 )AG, different from that of the Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites. According to the NCSL model, the volume strain of Al 2 O 3 /ZrO 2 , Al 2 O 3 /(5Re 0.2 )AG and ZrO 2 /(5Re 0.2 )AG phases was 0.576%, 0.668% and − 0.604%, respectively. The values were comparable, unlike the Al 2 O 3 /YAG/ZrO 2 eutectic ceramic composites where the volume strain of Al 2 O 3 /YAG was an order of magnitude larger than the other two. As a result, ZrO 2 was mostly diffusely and uniformly distributed in Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs in the form of fine round rods. The hardness, elastic modulus, and fracture toughness of Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs were significantly improved. This may be contributed to the solid solution (5Re 0.2 )AG, which tailored the orientation relationships of the Al 2 O 3 /(5Re 0.2 )AG/ZrO 2 eutectic HEOCs, redistributed ZrO 2 , refined the microstructure. Declarations Data availability The data that support the findings of this study are available from the corresponding author, Doc. Xu Wang, [email protected] , upon reasonable request. Author contribution Xu Wang supervised the project. Yujie Zhong and Xu Wang designed the experiments. Zhe Li performed the experiments. All authors discussed experiments and results. Yujie Zhong wrote the draft. Yujie Zhong and Xu Wang revised the manuscript. All authors have given approval for the final version of the manuscript. Funding This work was supported by the National Natural Science Foundation of China (grant numbers 52171046, 51804252), the Shaanxi Provincial Key Research and Development Program, China (No. 2021GY-133), and the Postgraduate Innovation and Practical Ability Training Program of Xi'an Shiyou University (No. YCS21212142). Conflict of interest The authors declare no competing interests. References Williams JC, Starke Jr EA (2003) Progress in structural materials for aerospace systems. Acta Mater 51:5775-5799. https://doi.org/10.1016/j.actamat.2003.08.023 Shen Z, Su H, Liu H et al (2022) Directly fabricated Al 2 O 3 /GdAlO 3 eutectic ceramic with large smooth surface by selective laser melting: Rapid solidification behavior and thermal field simulation. 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Acta Mater 39:1981-1994. https://doi.org/10.1016/0956-7151(91)90167-Y Gild J, Zhang Y, Harrington T et al (2016) High-entropy metal diborides: a new class of high-entropy materials and a new type of ultrahigh temperature ceramics. Sci Rep 37946. https://doi.org/10.1038/srep37946 Brown ID (2016) The chemical bond in inorganic chemistry: the bond valence model. Oxford university press. https://doi.org/10.1093/acprof:oso/9780199298815.001.0001 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3137798","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":219517752,"identity":"5d6e3a82-3762-453d-918d-383aa00a1870","order_by":0,"name":"Yujie Zhong","email":"","orcid":"","institution":"Xi'an Shiyou University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yujie","middleName":"","lastName":"Zhong","suffix":""},{"id":219517753,"identity":"9751ec78-de5e-4376-9844-acf09724e489","order_by":1,"name":"Zhe Li","email":"","orcid":"","institution":"Xi'an Shiyou University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Zhe","middleName":"","lastName":"Li","suffix":""},{"id":219517754,"identity":"a30f3c29-b491-4c7e-a276-4132d4cc4161","order_by":2,"name":"Xu Wang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA1UlEQVRIiWNgGAWjYNCCCgYZEHWABC1nGHhI1MLYBtFCHDC4kfzs4dd5djwG1w4wHrq5h0Gev4H52QN8WiRnpJkby25L5jG4ncBwOOcZg+GMA2zmBvi08EsnmElLbmOGajnAwLiBgYdNAp8WNun0b9KSc+rhWuwJauGXzjGT/NhwGK4lkaAWyflvyqQZjh3nkbyd2ADUIpE84zCbGV4tBmeOb5P8UVMtx3c7+fDnnAM2tv3tzc/wagEBZkikMDYACaBiZkLqQWp/EKFoFIyCUTAKRjAAABMKQ47SszshAAAAAElFTkSuQmCC","orcid":"","institution":"Chongqing University","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Xu","middleName":"","lastName":"Wang","suffix":""}],"badges":[],"createdAt":"2023-07-04 06:29:22","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3137798/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3137798/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":40384265,"identity":"992f0dd9-690a-4503-ac3c-40be00afcdb4","added_by":"auto","created_at":"2023-07-21 14:28:56","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":204677,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2 \u003c/sub\u003eeutectic HEOCs and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2 \u003c/sub\u003eeutectic ceramic composites powder samples in respective (a). (b) and (c) are enlarged patterns of the regions marked as b and c in (a), respectively.\u003c/p\u003e","description":"","filename":"floatimage1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3137798/v1/3829ea31abbc969b779a723b.jpg"},{"id":40383423,"identity":"70238c9c-50c1-434f-8364-215c63393260","added_by":"auto","created_at":"2023-07-21 14:20:56","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":748164,"visible":true,"origin":"","legend":"\u003cp\u003eTypical transverse SEM images of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2 \u003c/sub\u003eeutectic HEOCs (a) and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2 \u003c/sub\u003eeutectic ceramic composites (c). (b) and (d) the magnified areas marked in (a) and (c).\u003c/p\u003e","description":"","filename":"floatimage2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3137798/v1/8834d13d422754e89985951e.jpg"},{"id":40385234,"identity":"9b0f8f48-f134-4554-a7ac-606e99601781","added_by":"auto","created_at":"2023-07-21 14:36:56","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":350606,"visible":true,"origin":"","legend":"\u003cp\u003eTypical transverse sectional TEM results (a). The inserted patterns are the corresponding electron diffraction of the three phases. (b) and (c) HRTEM images of the (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG and YAG phases, respectively.\u003c/p\u003e","description":"","filename":"floatimage3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3137798/v1/48f5fc5e2ce1f55951326697.jpg"},{"id":40384266,"identity":"4a1eb80c-1054-435c-a9e6-32f5fb7558a9","added_by":"auto","created_at":"2023-07-21 14:28:56","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":773826,"visible":true,"origin":"","legend":"\u003cp\u003e(a) HAADF-STEM image of the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2 \u003c/sub\u003eeutectic HEOCs, (b) EDS analysis result along the direction indicated by the white line in Figure 4 (a). (c-j) the corresponding elemental mapping: (c) Y, (d) Yb, (e) Ho, (f) Lu, (g) Er, (h) Zr, (i) Al, and (j) O.\u003c/p\u003e","description":"","filename":"floatimage4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3137798/v1/e33e66d8aebeeb385515ec58.jpg"},{"id":40383425,"identity":"d3495c50-29d8-4e0e-9f21-019a60b4e032","added_by":"auto","created_at":"2023-07-21 14:20:56","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":377764,"visible":true,"origin":"","legend":"\u003cp\u003eTypical EBSD maps of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2 \u003c/sub\u003eeutectic HEOCs. (a) EBSD band-index maps. The dark is Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, the grey is the (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG and the white is ZrO\u003csub\u003e2\u003c/sub\u003e. (b), (c) and (d) EBSD maps of the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG and ZrO\u003csub\u003e2\u003c/sub\u003e, respectively. The color keys and the inverse pole figures are presented at the bottom right and left, respectively.\u003c/p\u003e","description":"","filename":"floatimage5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3137798/v1/6d7f741ae2003fcc4eaed28b.jpg"},{"id":40383419,"identity":"dc499078-329b-4100-9811-0a2f383e5227","added_by":"auto","created_at":"2023-07-21 14:20:56","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":312770,"visible":true,"origin":"","legend":"\u003cp\u003ePole figures of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, the (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG and ZrO\u003csub\u003e2\u003c/sub\u003e correspond to Figure 5, respectively.\u003c/p\u003e","description":"","filename":"floatimage6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3137798/v1/3df86b329a7a1c876c48caf5.jpg"},{"id":40383416,"identity":"a20db9ab-78e7-4382-9abb-682cdcc809ac","added_by":"auto","created_at":"2023-07-21 14:20:56","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":789431,"visible":true,"origin":"","legend":"\u003cp\u003eTEM results of the three interfaces. (a), (d) and (g) are HRTEM images of the interfaces marked in Figure 3 along parallel axes of I: [1-100] Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e || [100] ZrO\u003csub\u003e2\u003c/sub\u003e (a), II: [103] (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG || [100] ZrO\u003csub\u003e2\u003c/sub\u003e (d) and III: [103] (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG || [1-100] Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3 \u003c/sub\u003e(g); (b), (e) and (h) are electron diffraction patterns at interface of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/ZrO\u003csub\u003e2\u003c/sub\u003e, (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG, respectively. (c), (f) and (i) are one-dimensional Fourier-filtered images by the pair patterns circled by the red circle in the FFT maps of (a), (d) and (g), showing the periods of the misfit dislocation at every interface.\u003c/p\u003e","description":"","filename":"floatimage7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3137798/v1/64950233ebddb0e30fc9c503.jpg"},{"id":40384267,"identity":"7717bdfe-0793-413b-8152-3100a4d87962","added_by":"auto","created_at":"2023-07-21 14:28:56","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":136180,"visible":true,"origin":"","legend":"\u003cp\u003eThe measured microhardness of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2 \u003c/sub\u003eeutectic HEOCs and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2 \u003c/sub\u003eeutectic ceramic composites as a function of the applied load.\u003c/p\u003e","description":"","filename":"floatimage8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3137798/v1/d1fa6a88e1fcf98b2f4106c0.jpg"},{"id":40383422,"identity":"53f7e110-0da7-4184-a36c-fe2b159f3dde","added_by":"auto","created_at":"2023-07-21 14:20:56","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":183453,"visible":true,"origin":"","legend":"\u003cp\u003eCombined electron diffraction patterns of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e (a) and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e (b). The black, blue and red dots mean electron diffraction patterns of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG (or YAG) and c-ZrO\u003csub\u003e2\u003c/sub\u003e, respectively.\u003c/p\u003e","description":"","filename":"floatimage9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3137798/v1/c00f3f9a36c76ca9bfec94b2.jpg"},{"id":40383418,"identity":"dc07ec7f-c876-48f3-909a-137d71a1c999","added_by":"auto","created_at":"2023-07-21 14:20:56","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":272754,"visible":true,"origin":"","legend":"\u003cp\u003e3D lattice model showing the orientation relationship of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2 \u003c/sub\u003eeutectic ceramic composites (a) and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2 \u003c/sub\u003eeutectic HEOCs (b).\u003c/p\u003e","description":"","filename":"floatimage10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3137798/v1/56d4ad85ebebc607e7be8bf1.jpg"},{"id":40383426,"identity":"580898b8-4889-45bc-90a2-4d1763b93f4e","added_by":"auto","created_at":"2023-07-21 14:20:56","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":312481,"visible":true,"origin":"","legend":"\u003cp\u003eNCSL models in (a) {10-10} Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e || {001} ZrO\u003csub\u003e2\u003c/sub\u003e planes, (b) {001} ZrO\u003csub\u003e2\u003c/sub\u003e || {103} (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG planes and (c) {10-10} Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e || {103} (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG planes. The black line indicates the lattice of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, the blue line indicates the lattice of ZrO\u003csub\u003e2\u003c/sub\u003e and the orange line indicates the lattice of (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG.\u003c/p\u003e","description":"","filename":"floatimage11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3137798/v1/0b5702c112d7c866c67bce3c.jpg"},{"id":40520879,"identity":"5e24537e-e27c-4359-a6fe-68031e27e00a","added_by":"auto","created_at":"2023-07-25 08:52:38","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2337949,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3137798/v1/76560969-68d3-4736-8250-8c98f10000a3.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Insight into tuning of ZrO2 distribution and mechanical properties of directionally solidified Al2O3/(5Re0.2)AG/ZrO2 eutectic ceramic composites","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eHigh-performance aero-engines put forward higher requirements on the temperature-bearing capacity of turbine blade materials. For example, the turbine inlet temperature of an engine with a thrust-to-weight ratio of 10 or more is up to 1600 \u003csup\u003eo\u003c/sup\u003eC-1650 \u003csup\u003eo\u003c/sup\u003eC [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Directionally solidified Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-based eutectic ceramic composites with high melting point (~\u0026thinsp;1800 \u003csup\u003eo\u003c/sup\u003eC), outstanding high-temperature creep and oxidation resistance are considered to be one of the next generation of ultra-high temperature structural materials [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Previous studies have shown that if they can be applied as a guide vane or combustion chamber liner, it could significantly improve the thrust-to-weight ratio of an engine and thermal efficiency will also increase by 9% [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. However, the poor fracture toughness and high-temperature strength limit their application as a high-temperature structural material.\u003c/p\u003e \u003cp\u003eSeveral classes of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-based directionally solidified ceramic composites have been widely studied, such as binary eutectics Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/Y\u003csub\u003e3\u003c/sub\u003eAl\u003csub\u003e5\u003c/sub\u003eO\u003csub\u003e12\u003c/sub\u003e [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/Ed\u003csub\u003e3\u003c/sub\u003eAl\u003csub\u003e5\u003c/sub\u003eO\u003csub\u003e12\u003c/sub\u003e [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/GdAlO\u003csub\u003e3\u003c/sub\u003e [\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/SmAlO\u003csub\u003e3\u003c/sub\u003e [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] and ternary eutectics Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/Y\u003csub\u003e3\u003c/sub\u003eAl\u003csub\u003e5\u003c/sub\u003eO\u003csub\u003e12\u003c/sub\u003e(YAG)/ZrO\u003csub\u003e2\u003c/sub\u003e [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/Ed\u003csub\u003e3\u003c/sub\u003eAl\u003csub\u003e5\u003c/sub\u003eO\u003csub\u003e12\u003c/sub\u003e/ZrO\u003csub\u003e2\u003c/sub\u003e [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. In general, the fracture toughness of ternary eutectics is higher than that of binary eutectics due to the addition of ZrO\u003csub\u003e2\u003c/sub\u003e [\u003cspan additionalcitationids=\"CR18 CR19 CR20\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. The introduction of ZrO\u003csub\u003e2\u003c/sub\u003e makes the ternary eutectic layer finer than the binary eutectic layer under the same solidification process, which improves its bending strength [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. The crack kinked [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], deflected [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e] at ZrO\u003csub\u003e2\u003c/sub\u003e, or even was prevented by ZrO\u003csub\u003e2\u003c/sub\u003e [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. ZrO\u003csub\u003e2\u003c/sub\u003e acts as the toughening phase, and its morphology, size and distribution play a decisive role in the toughening effect.\u003c/p\u003e \u003cp\u003eHowever, according to the morphology of directionally solidified Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites reported in literature [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan additionalcitationids=\"CR26 CR27 CR28 CR29\" citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e], it is found that ZrO\u003csub\u003e2\u003c/sub\u003e was mainly distributed between Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and YAG in the form of fine round rods or lamellae, and a small amount located in Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, and a very small amount in YAG. It evidently shows that the morphology and distribution of ZrO\u003csub\u003e2\u003c/sub\u003e are not random, but are governed by certain laws. Our previous work found that the distribution of ZrO\u003csub\u003e2\u003c/sub\u003e was mainly dominated by the minimization of the interfacial strain energy. In directionally solidified Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites, the mismatch strain of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-YAG, Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-ZrO\u003csub\u003e2\u003c/sub\u003e, and YAG-ZrO\u003csub\u003e2\u003c/sub\u003e is -0.9%, -0.1% and 0.2%, respectively [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], which imply that the interfacial strain energy of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-YAG is much higher than that of YAG-ZrO\u003csub\u003e2\u003c/sub\u003e and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-ZrO\u003csub\u003e2\u003c/sub\u003e. To minimize the total interfacial strain energy of the eutectic system, ZrO\u003csub\u003e2\u003c/sub\u003e diffuses and distributes between Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and YAG with the largest possible surface area (i.e., rod or lamellar) to reduce the interface area formed by YAG and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e phase, which has the largest interfacial strain energy. This heterogeneous distribution of ZrO\u003csub\u003e2\u003c/sub\u003e weakens its strengthening and toughening effect. It is expected that ZrO\u003csub\u003e2\u003c/sub\u003e can be homogeneously distributed in Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, YAG, and between the two, to achieve the best strengthening and toughening effect. Therefore, the authors envision if the distribution of ZrO\u003csub\u003e2\u003c/sub\u003e could be modified by tuning the interfacial mismatch.\u003c/p\u003e \u003cp\u003eThe solid solution will lead to lattice distortion, which becomes more severe as the number of solid solution elements increases [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. Lattice distortion is bound to cause changes in the \u003cem\u003ed\u003c/em\u003e-spacing. Therefore, the solid solution seems to be an effective way to tailor the interfacial mismatch. Recently, high-entropy ceramic composites, which are commonly referred to as a solid solution formed by four or more ceramic components, have shown unexpected properties such as high hardness, superior elastic modulus as well as high fracture toughness [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. For example, the fracture toughness of (Ti\u003csub\u003e0.2\u003c/sub\u003eZr\u003csub\u003e0.2\u003c/sub\u003eHf\u003csub\u003e0.2\u003c/sub\u003eNb\u003csub\u003e0.2\u003c/sub\u003eTa\u003csub\u003e0.2\u003c/sub\u003e)(C\u003csub\u003e0.5\u003c/sub\u003eN\u003csub\u003e0.5\u003c/sub\u003e) is 8.4 MPa\u0026middot;m\u003csup\u003e1/2\u003c/sup\u003e, much higher than that of binary ceramic composites [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. The fracture toughness of (Zr\u003csub\u003e0.25\u003c/sub\u003eNb\u003csub\u003e0.25\u003c/sub\u003eTi\u003csub\u003e0.25\u003c/sub\u003eV\u003csub\u003e0.25\u003c/sub\u003e)C is up to 4.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5 MPa\u0026middot;m\u003csup\u003e1/2\u003c/sup\u003e, larger than that of the individual component [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. The above studies suggest that in addition to raising the performance of high-entropy ceramic composites, the solid solution may also tune the interfacial structure formed by the high-entropy with other phases through lattice distortion, thereby further optimizing the mechanical properties.\u003c/p\u003e \u003cp\u003eIn the present work, the YAG phase in Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites is replaced by an oxide solid solution (Y\u003csub\u003e0.2\u003c/sub\u003eEr\u003csub\u003e0.2\u003c/sub\u003eYb\u003csub\u003e0.2\u003c/sub\u003eHo\u003csub\u003e0.2\u003c/sub\u003eLu\u003csub\u003e0.2\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003eAl\u003csub\u003e5\u003c/sub\u003eO\u003csub\u003e12\u003c/sub\u003e, and directionally solidified Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(Y\u003csub\u003e0.2\u003c/sub\u003eEr\u003csub\u003e0.2\u003c/sub\u003eYb\u003csub\u003e0.2\u003c/sub\u003eHo\u003csub\u003e0.2\u003c/sub\u003eLu\u003csub\u003e0.2\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003eAl\u003csub\u003e5\u003c/sub\u003eO\u003csub\u003e12\u003c/sub\u003e((5Re\u003csub\u003e0.2\u003c/sub\u003e)AG)/ZrO\u003csub\u003e2\u003c/sub\u003e ternary eutectic high entropy oxide ceramic composites (HEOCs) is prepared with an optical floating zone furnace. The as-prepared eutectic HEOCs are composed of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, the (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG, and ZrO\u003csub\u003e2\u003c/sub\u003e single-crystal phases. The effect of the lattice distortion of (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG on the distribution of ZrO\u003csub\u003e2\u003c/sub\u003e and interfacial structure is reported for the first time. Mechanical properties including nano/Vickers hardness, elastic modulus, and fracture toughness of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs are studied and compared with those of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites. These results may cast light for optimizing the mechanical properties of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-based eutectic ceramic composites.\u003c/p\u003e"},{"header":"2. Experimental section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Preparation of samples and direction solidification\u003c/h2\u003e \u003cp\u003eCommercially available ceramic powders of Re\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (Re\u0026thinsp;=\u0026thinsp;Y, Lu, Ho, Er and Yb, 99.99% purity), ZrO\u003csub\u003e2\u003c/sub\u003e (99.99% purity), and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (99.95% purity) were used to prepare the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs. Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, Re\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and ZrO\u003csub\u003e2\u003c/sub\u003e powders were mixed with a molar ratio of 65:16:19 according to the eutectic point in the ternary phase diagram [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Re\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e powders were mixed in equal molar fractions. Then the prepared powder was wet ball milled with alcohol for 12 h to ensure homogeneity. The slurry was dried and sieved through a 120-mesh net to obtain the requested powders. Precursors were prepared by holding at 45 MPa for 5 minutes in a stainless-steel mold with a dimension of 10 \u0026times; 10 \u0026times; 100 mm\u003csup\u003e3\u003c/sup\u003e and then sintering without pressure in a muffle furnace at 1823 K for 2.5 h.\u003c/p\u003e \u003cp\u003eThe directional solidification process was carried out in an optical floating zone (OFZ) furnace with a slight overpressure (~\u0026thinsp;1.1 bars) in an argon atmosphere. During the preparation process, precursors were melted using four 3 kW xenon arc lamps with a withdrawal rate of 20 mm/h. The prepared crystals measured up to 120 mm in length and about 10 mm in diameter.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Microstructure characterization\u003c/h2\u003e \u003cp\u003eThe as-prepared Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOC bars and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic bars were sliced by wire-cutting equipment. Samples were well grounded with 600#, 1000# diamond discs, and SiC paper up to 2000#. They were further polished using 2.5 \u0026micro;m diamond paste. TEM samples were prepared using a dual-beam focused ion beam (FIB, Thermo Scientific Scios 2, USA).\u003c/p\u003e \u003cp\u003eThe phase composition was analyzed employing an X-ray diffractometer (LabX XRD-6000, Japan). The microstructure was characterized using scanning electron microscopy (SEM, JSM-6700 F, JEOL, Japan). Orientation relationships were determined with electron-back scattered diffraction (EBSD, NordlysNano, Oxfordshire, UK). A 300 kV transmission electron microscopy (TEM, FEI Talos F300C, U) equipped with an energy dispersive X-ray spectroscopy (EDS) analysis unit was used for high-resolution transmission electron microscopy (HRTEM) observation and EDS elemental analysis.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Mechanical properties testing\u003c/h2\u003e \u003cp\u003eThe Vickers hardness was obtained using a Vickers Indenter (HVS-10AT, China) when loaded at 2.94, 4.9, 9.8, 19.6, 29.4, and 49 N. The holding time is 15 s. In addition, the fracture toughness (\u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003eIC\u003c/em\u003e\u003c/sub\u003e) was measured on the basis of the indentation method using the following equation[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]:\u003c/p\u003e \u003cp\u003eK\u003csub\u003eIC\u003c/sub\u003e = 0.016 \u0026times; (E/H\u003csub\u003eV\u003c/sub\u003e)\u003csup\u003e1/2\u003c/sup\u003ep/c\u003csup\u003e3/2\u003c/sup\u003e (1)\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003eE\u003c/em\u003e is Young's modulus, \u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003eV\u003c/em\u003e\u003c/sub\u003e is the Vickers hardness, \u003cem\u003ec\u003c/em\u003e is the half-length indentation diagonal and \u003cem\u003ep\u003c/em\u003e is the indentation load. Nanoindentation tests were performed on well-polished sample surfaces employing a Nano-Indenter G200 (KLA, USA) system equipped with a diamond Berkovich indenter with a 20 nm tip radius to evaluate their nanohardness and elastic modulus. The maximum load for nanoindentation mapping was 29 mN and the indentation spacing was 10 \u0026micro;m.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Microstructure of the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e ternary eutectic HEOCs\u003c/h2\u003e \u003cp\u003eThe composition of the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs was investigated by the XRD technique and compared with Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. In comparison with standard PDF cards, the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs consist of three phases: Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, the (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG and cubic ZrO\u003csub\u003e2\u003c/sub\u003e (c-ZrO\u003csub\u003e2\u003c/sub\u003e). Taking a careful observation of the magnified regions b and c, it is found that neither the (1 0 4) peak position of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e nor the (2 0 0) peak position of ZrO\u003csub\u003e2\u003c/sub\u003e shifts, while the (4 2 0) peak position of the (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG shifts towards the high angle in contrast to Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/Y\u003csub\u003e3\u003c/sub\u003eA\u003csub\u003e5\u003c/sub\u003eO\u003csub\u003e12\u003c/sub\u003e/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites. The shift is more pronounced at the high-angle peak position, which means a reduction of \u003cem\u003ed\u003c/em\u003e-spacing of the (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG phase according to the Bragg equation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe transverse microstructures of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites are displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Both of the eutectics have a so-called \u003cem\u003eChinese-script\u003c/em\u003e microstructure. The dark area is Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e phase, the grey area is the (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG or YAG phase and the white area is ZrO\u003csub\u003e2\u003c/sub\u003e phase. Comparing Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea and c at the same magnification, it is found that the microstructure size of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs is finer and more diffuse under the same solidification process. It is about 1/2 to 1/3 of that of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites. Especially for ZrO\u003csub\u003e2\u003c/sub\u003e phase, comparing Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb and d, the size of ZrO\u003csub\u003e2\u003c/sub\u003e tissue in Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs is about 1/4 to 1/3 of that in Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites. In addition, the morphology and distribution of ZrO\u003csub\u003e2\u003c/sub\u003e in the two eutectics are also different. In Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites, ZrO\u003csub\u003e2\u003c/sub\u003e is mainly distributed at the interface between Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and YAG in the form of thin laminate and round rod-like shape, as reported previously [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. However, in the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs, ZrO\u003csub\u003e2\u003c/sub\u003e is rather well-distributed both in the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG and their interface with a tiny round rod-like shape.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe microstructure of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs was further observed by TEM, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea. It can be seen that the three phases are well-boned by interfaces, which are clean and smooth, with no intermediate phase or amorphous phase. According to the different electron diffraction patterns, the white is Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, the light gray is the (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG, and the dark gray is c-ZrO\u003csub\u003e2\u003c/sub\u003e. XRD results signify that there is a change in the \u003cem\u003ed\u003c/em\u003e-spacing of the (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG compared to the YAG. To verify the XRD result, the \u003cem\u003ed\u003c/em\u003e-spacings of both (0 2 0) planes of two were carefully measured based on the electron diffraction patterns, as marked in HRTEM maps (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb and c). The \u003cem\u003ed\u003c/em\u003e-spacing of (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG (0 2 0) plane is 0.5894 nm, smaller than that of the YAG (0 2 0) plane (0.6004 nm). To check our measurement results, the \u003cem\u003ed\u003c/em\u003e-spacing of (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG (3 0\u0026ndash;1) was measured and compared with that of (3 0 1) calculated by measured (0 2 0). The two values were found to be consistent. The results indicate that the (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG lattice is negatively distorted compared with YAG, which agrees well with the XRD results.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eScanning transmission electron microscopy (STEM) is employed for the investigation of element distribution of the as-grown Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs, as presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. According to the EDS line scan results shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb, five cations (i.e., Y\u003csup\u003e3+\u003c/sup\u003e, Er\u003csup\u003e3+\u003c/sup\u003e, Ho\u003csup\u003e3+\u003c/sup\u003e, Lu\u003csup\u003e3+\u003c/sup\u003e and Yb\u003csup\u003e3+\u003c/sup\u003e) have almost the same composition of ~\u0026thinsp;20% as expected. Some of the Y, Yb, Er, Ho, Lu and Al elements are solved into the ZrO\u003csub\u003e2\u003c/sub\u003e phase, which play a role in stabilizing its cubic crystal structure. Figures\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec-g show a highly homogenous distribution of Y, Er, Yb, Ho, and Lu elements in the (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG phase, indicating that the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs are well fabricated.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Orientation relationships the interfaces\u003c/h2\u003e \u003cp\u003eThe orientation relationships of the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs are examined by EBSD, and the result is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. Figures\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb-d show the preferred growth direction of the three phases, respectively, \u0026lt;\u0026thinsp;10\u0026ndash;10\u0026thinsp;\u0026gt;\u0026thinsp;for Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (the two colors mean the same direction of \u0026lt;\u0026thinsp;10\u0026ndash;10\u0026gt; [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]), \u0026lt;\u0026thinsp;103\u0026thinsp;\u0026gt;\u0026thinsp;for the (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG, and \u0026lt;\u0026thinsp;100\u0026thinsp;\u0026gt;\u0026thinsp;for ZrO\u003csub\u003e2\u003c/sub\u003e. At first glance, Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs has the same preferred growth directions as Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites reported in the literature [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. However, further analysis of the inverse polar figure (lower left corner in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec) demonstrates that the preferred growth direction of (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG is \u0026lt;\u0026thinsp;103\u0026gt;, exactly. Therefore, the preferred growth directions are:\u003c/p\u003e \u003cp\u003e\u0026lt;\u0026thinsp;10\u0026ndash;10\u0026thinsp;\u0026gt;\u0026thinsp;Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e || \u0026lt;103\u0026gt; (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG || \u0026lt;100\u0026thinsp;\u0026gt;\u0026thinsp;ZrO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e exhibits the pole figures of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, the (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG, and ZrO\u003csub\u003e2\u003c/sub\u003e shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. It can be obtained that the orientation relationships of the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs are:\u003c/p\u003e \u003cp\u003e{11\u0026ndash;20} Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e || {100} (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG || {100} ZrO\u003csub\u003e2\u003c/sub\u003e, and\u003c/p\u003e \u003cp\u003e{0001} Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e || {103} (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG || {100} ZrO\u003csub\u003e2\u003c/sub\u003e, as circled by the red circles and black circles in Figs.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea, b and c, respectively. In general, the orientation relationships of the three eutectic phases are summarized as follows:\u003c/p\u003e \u003cp\u003e\u0026lt;\u0026thinsp;10\u0026ndash;10\u0026thinsp;\u0026gt;\u0026thinsp;Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e || \u0026lt;103\u0026gt; (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG || \u0026lt;100\u0026thinsp;\u0026gt;\u0026thinsp;ZrO\u003csub\u003e2\u003c/sub\u003e (white circles),\u003c/p\u003e \u003cp\u003e{11\u0026ndash;20} Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e || {100} (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG || {100} ZrO\u003csub\u003e2\u003c/sub\u003e (black circles),\u003c/p\u003e \u003cp\u003e{0001} Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e || {103} (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG || {100} ZrO\u003csub\u003e2\u003c/sub\u003e (red circles).\u003c/p\u003e \u003cp\u003eNotably, the orientation relationships of directionally solidified Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs are different from that of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo further investigate the orientation relationship interfacial structure of the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs, thin-foil samples were prepared for the HRTEM tests. Figures\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea, d and g show the HRTEM images of the three interfaces marked by the red squares in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. Interface I is Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/ZrO\u003csub\u003e2\u003c/sub\u003e, interface II is ZrO\u003csub\u003e2\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG and interface III is Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG. It can be seen that all three interfaces are clean and well-oriented. From the corresponding selected-area diffraction patterns of the interfaces, depicted in Figs.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb, e and h, the orientation relationship of the three interfaces are:\u003c/p\u003e \u003cp\u003eInterface I: [1-100] (11\u0026ndash;20) Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e || [100] (020) ZrO\u003csub\u003e2\u003c/sub\u003e,\u003c/p\u003e \u003cp\u003eInterface II: [100] (020) ZrO\u003csub\u003e2\u003c/sub\u003e || [103] (040) (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG,\u003c/p\u003e \u003cp\u003eInterface III: [1-100] (11\u0026ndash;20) Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e || [103] (040) (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG,\u003c/p\u003e \u003cp\u003ewhich are the same as that obtained from the EBSD experiments. These well-oriented interfaces are semi-coherent, as shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ec, f and i. The lattice misfit is accommodated by a series of periodic misfit dislocations. The periods of the misfit dislocation in sequence are 1/13 for Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/ZrO\u003csub\u003e2\u003c/sub\u003e, 1/7 for ZrO\u003csub\u003e2\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG and 1/5 for Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Mechanical properties\u003c/h2\u003e \u003cp\u003eTo compare and study the influence of (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG instead of YAG, mechanical properties including nanohardness, Vickers hardness, elastic modulus, and fracture toughness of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites prepared by the same process were studied at the same time.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e shows the Vickers hardness of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites under different applied loads. It can be found that the microhardness of both samples decreases with the increasing load. This may be due to the porosity in the ceramic composites. However, the Vickers hardness of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs is higher than that of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites. At a load of 9.8 N, the Vickers hardness of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs is about 19.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4 GPa and that of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites is about 16.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.57 GPa.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe nanoindentation method was used to test the nanohardness and elastic modulus of the two samples, as summarized in Table I. The nanohardness of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs is 33.17\u0026thinsp;\u0026plusmn;\u0026thinsp;0.52 GPa, higher than 21.66\u0026thinsp;\u0026plusmn;\u0026thinsp;0.43 GPa of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites. The elastic modulus is 436.1\u0026thinsp;\u0026plusmn;\u0026thinsp;6.7 GPa, while that of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites is 357.8\u0026thinsp;\u0026plusmn;\u0026thinsp;8.9 GPa. It is worth mentioning that the elastic modulus is not only higher than that of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites but also higher than that of their component. The fracture toughness is estimated based on the indentation method with a load of 49 N. The fracture toughness is calculated to be 8.55\u0026thinsp;\u0026plusmn;\u0026thinsp;0.36 MPa/m\u003csup\u003e1/2\u003c/sup\u003e, almost 2.5 times that of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites (3.54\u0026thinsp;\u0026plusmn;\u0026thinsp;0.34 MPa/m\u003csup\u003e1/2\u003c/sup\u003e).\u003c/p\u003e \u003cp\u003eTable I. The measured nanohardness, elastic modulus, and fracture toughness of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites prepared with the same solidification process.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSamples\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNanohardness (GPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eElastic modulus (GPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFracture toughness\u003c/p\u003e \u003cp\u003e(K\u003csub\u003eIC\u003c/sub\u003e, MPa/m\u003csup\u003e1/2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e33.17\u0026thinsp;\u0026plusmn;\u0026thinsp;0.52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e436.1\u0026thinsp;\u0026plusmn;\u0026thinsp;6.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e8.55\u0026thinsp;\u0026plusmn;\u0026thinsp;0.36\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e21.66\u0026thinsp;\u0026plusmn;\u0026thinsp;0.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e357.8\u0026thinsp;\u0026plusmn;\u0026thinsp;8.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e3.54\u0026thinsp;\u0026plusmn;\u0026thinsp;0.34\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Distribution of ZrO\u003csub\u003e2\u003c/sub\u003e\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e illustrates the combined orientation relationships between Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, the (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG and ZrO\u003csub\u003e2\u003c/sub\u003e obtained from the above experimental results, together with that of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e of our previous work [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] for comparison. The difference was marked with a pink dashed rectangle. It can be seen qualitatively that the mismatch between (0003)Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and (30\u0026thinsp;\u0026minus;\u0026thinsp;1)(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG in Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs is significantly smaller than that between (0003)Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and (004)YAG in Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites. That is to say, the mismatch difference between Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/ZrO\u003csub\u003e2\u003c/sub\u003e and (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e in Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs is small, but that between Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/ZrO\u003csub\u003e2\u003c/sub\u003e and YAG/ZrO\u003csub\u003e2\u003c/sub\u003e in Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites is relatively large. Therefore, ZrO\u003csub\u003e2\u003c/sub\u003e in Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs can be distributed in both Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG, and between them, making ZrO\u003csub\u003e2\u003c/sub\u003e homogenously dispersed without segregation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAccording to the measured \u003cem\u003ed\u003c/em\u003e-spacing in Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb and c, the lattice constant of the (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG phase is calculated to be 1.1788 nm, smaller than 1.2008 nm of the YAG phase. It can be inferred that the lattice distortion leads to a change in the crystal orientation relationship, as clearly illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e. Comparing Figs.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ea and b, the preferred growth direction of (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG changes to be [103] and the parallel plane changes to be {-301}. However, the orientation relationship of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and ZrO\u003csub\u003e2\u003c/sub\u003e remains unchanged.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo quantitatively investigate the effect of the change of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs orientation relationship on the interfacial strain, the 3D lattice matching of the interfaces is investigated by the near-coincident site lattice (NCSL) theory. Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e is a rhombohedral structure with a\u0026thinsp;=\u0026thinsp;0.47544 nm and c\u0026thinsp;=\u0026thinsp;1.29725 nm. The (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG is a cubic structure, with a\u0026thinsp;=\u0026thinsp;1.1788 nm. And ZrO\u003csub\u003e2\u003c/sub\u003e is a cubic structure with a\u0026thinsp;=\u0026thinsp;0.51523 nm. All lattice constants are derived from the average of multiple measurements of the \u003cem\u003ed\u003c/em\u003e-spacings in HRTEM. In the NCSL analysis, a typically used tolerance factor of 0.05 nm is applied to define 'near-coincident sites' [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. The projections of the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, ZrO\u003csub\u003e2\u003c/sub\u003e and (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG lattices along the parallel axes of [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e || [100] ZrO\u003csub\u003e2\u003c/sub\u003e, [103] (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG || [100] ZrO\u003csub\u003e2\u003c/sub\u003e and [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e || [103] (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG, are displayed in Figs.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003ea, b and c, respectively. The so-called smallest NCSL models along the parallel axes are formed by vectors, as listed in Table II.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTable II. The smallest NCSL model of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs formed by vectors along the parallel axes.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Tabb\" border=\"1\"\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e || [100] ZrO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e[103] (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG || [100] ZrO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e || [103] (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eu\u003c/b\u003e\u003csub\u003e\u003cb\u003e1\u003c/b\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;4[001]ZrO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;5[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eu\u003c/b\u003e\u003csub\u003e\u003cb\u003e1\u003c/b\u003e\u003c/sub\u003e'=5[001]ZrO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;7[103](5Re\u003csub\u003e0.2\u003c/sub\u003e)AG\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eu\u003c/b\u003e\u003csub\u003e\u003cb\u003e1\u003c/b\u003e\u003c/sub\u003e\"=11[103](5Re\u003csub\u003e0.2\u003c/sub\u003e)AG\u0026thinsp;\u0026asymp;\u0026thinsp;10[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eu\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;5[100]ZrO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;6[0003]Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eu\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e'=5[100]ZrO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;7[30\u0026thinsp;\u0026minus;\u0026thinsp;1](5Re\u003csub\u003e0.2\u003c/sub\u003e)AG\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eu\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\"=7[30\u0026thinsp;\u0026minus;\u0026thinsp;1](5Re\u003csub\u003e0.2\u003c/sub\u003e)AG\u0026thinsp;\u0026asymp;\u0026thinsp;6[0003]Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eu\u003c/b\u003e\u003csub\u003e\u003cb\u003e3\u003c/b\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;6[010]ZrO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;13[1-210]Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eu\u003c/b\u003e\u003csub\u003e\u003cb\u003e3\u003c/b\u003e\u003c/sub\u003e'=7[010]ZrO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;12[040](5Re\u003csub\u003e0.2\u003c/sub\u003e)AG\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eu\u003c/b\u003e\u003csub\u003e\u003cb\u003e3\u003c/b\u003e\u003c/sub\u003e\"=4[040](5Re\u003csub\u003e0.2\u003c/sub\u003e)AG\u0026thinsp;\u0026asymp;\u0026thinsp;5[1-210] Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe volumetric strain between the NCSL models referred to each lattice can be calculated by [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\begin{array}{c} {\\epsilon }_{{v}_{{Al}_{2}{O}_{3}-Zr{O}_{2}}}= \\frac{{V}_{NCSL-{Al}_{2}{O}_{3}}-{V}_{NCSL-Zr{O}_{2}}}{{(V}_{NCSL-{Al}_{2}{O}_{3}}+{V}_{NCSL-Zr{O}_{2}})/2}\\#\\left(2\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\begin{array}{c}{\\epsilon }_{{v}_{{Al}_{2}{O}_{3}-\\left(5{Re}_{0.2}\\right)AG}}= \\frac{{V}_{NCSL-{Al}_{2}{O}_{3}}-{V}_{NCSL-\\left(5{Re}_{0.2}\\right)AG}}{{(V}_{NCSL-{Al}_{2}{O}_{3}}+{V}_{NCSL-\\left(5{Re}_{0.2}\\right)AG})/2}\\#\\left(3\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e\n$$\\begin{array}{c}{\\epsilon }_{{v}_{{ZrO}_{2}-\\left(5{Re}_{0.2}\\right)AG}}= \\frac{{{V}_{NCSL-Zr{O}_{2}}-V}_{NCSL-\\left(5{Re}_{0.2}\\right)AG}}{{(V}_{NCSL-\\left(5{Re}_{0.2}\\right)AG}+{V}_{NCSL-Zr{O}_{2}})/2}\\#\\left(4\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({V}_{NCSL-{Al}_{2}{O}_{3}}\\)\u003c/span\u003e\u003c/span\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({V}_{NCSL-Zr{O}_{2}}\\)\u003c/span\u003e\u003c/span\u003eand \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({V}_{NCSL-\\left(5{Re}_{0.2}\\right)AG}\\)\u003c/span\u003e\u003c/span\u003e are volumes of the NCSL unit cells of the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, ZrO\u003csub\u003e2\u003c/sub\u003e and (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG lattices, respectively. The volumetric strain is computed to be 0.576% for \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\epsilon }_{{v}_{{Al}_{2}{O}_{3}-Zr{O}_{2}}}\\)\u003c/span\u003e\u003c/span\u003e, 0.668% for \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\epsilon }_{{v}_{{Al}_{2}{O}_{3}-\\left(5{Re}_{0.2}\\right)AG}}\\)\u003c/span\u003e\u003c/span\u003e and \u0026minus;\u0026thinsp;0.604% for \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\epsilon }_{{v}_{{ZrO}_{2}-\\left(5{Re}_{0.2}\\right)AG}}\\)\u003c/span\u003e\u003c/span\u003e. Calculations indicate that the volume strains of the three phases are almost identical, implying the almost same interfacial strain energy.\u003c/p\u003e \u003cp\u003eFor comparison, the smallest NCSL model of the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites along the parallel axes is also formed by vectors, as detailed in Table III. Moreover, the volume strain is calculated to be 0.576% for \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\epsilon }_{{v}_{{Al}_{2}{O}_{3}-Zr{O}_{2}}}\\)\u003c/span\u003e\u003c/span\u003e, -2.3% for \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\epsilon }_{{v}_{{Al}_{2}{O}_{3}-YAG}}\\)\u003c/span\u003e\u003c/span\u003e, and 0.295% for \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\epsilon }_{{v}_{{ZrO}_{2}-YAG}}\\)\u003c/span\u003e\u003c/span\u003e. Apparently, the value of \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\epsilon }_{{v}_{{Al}_{2}{O}_{3}-YAG}}\\)\u003c/span\u003e\u003c/span\u003e is an order of magnitude greater than the other two. The results verified the results previously reported in the literature [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. According to the principle of minimizing the interfacial strain energy of the system, ZrO\u003csub\u003e2\u003c/sub\u003e tends to distribute between Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and YAG, so as to suppress the formation of the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG interface having high interfacial strain. However, the volume strain differences of the three interfaces in Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs are very small, making ZrO\u003csub\u003e2\u003c/sub\u003e phase uniformly distributed in Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, the (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG, and between them.\u003c/p\u003e \u003cp\u003eTable III. The smallest NCSL model of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites formed by vectors along the parallel axes.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Tabc\" border=\"1\"\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e || [100] ZrO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e[100] YAG || [100] ZrO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e || [100] YAG\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eu\u003c/b\u003e\u003csub\u003e\u003cb\u003e1\u003c/b\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;4[001]ZrO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;5[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eu\u003c/b\u003e\u003csub\u003e\u003cb\u003e1\u003c/b\u003e\u003c/sub\u003e'=7[001]ZrO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;12[004]YAG\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eu\u003c/b\u003e\u003csub\u003e\u003cb\u003e1\u003c/b\u003e\u003c/sub\u003e\"=4[004]YAG\u0026thinsp;\u0026asymp;\u0026thinsp;3[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eu\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;5[100]ZrO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;6[0003]Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eu\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e'=7[100]ZrO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;12[400]YAG\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eu\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\"=3[400]YAG\u0026thinsp;\u0026asymp;\u0026thinsp;2[0003]Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eu\u003c/b\u003e\u003csub\u003e\u003cb\u003e3\u003c/b\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;12[020]ZrO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;13[1-210]Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eu\u003c/b\u003e\u003csub\u003e\u003cb\u003e3\u003c/b\u003e\u003c/sub\u003e'=7[020]ZrO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;6[040]YAG\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eu\u003c/b\u003e\u003csub\u003e\u003cb\u003e3\u003c/b\u003e\u003c/sub\u003e\"=4[040]YAG\u0026thinsp;\u0026asymp;\u0026thinsp;5[1-210] Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Effect of microstructure on mechanical performance\u003c/h2\u003e \u003cp\u003eIt is obvious that the mechanical properties of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs are better than Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites. The reasons are generally attributed to (i) the substitution of YAG with (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG, (ii) tailored interfacial structure, and (iii) the homogeneous distribution of ZrO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the eutectic microstructure of directionally solidified Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs is much finer compared to Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites prepared with the same preparation process. This can be attributed to the 'hysteresis diffusion' effect of high-entropy materials [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. During the liquid-solid transition, the atoms of each group diffuse corporately from a chaotic state to an ordered state. There are more atoms in the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs, leading to a relatively low diffusion rate and thus inhibiting the growth of the lamellae. Therefore, compared with Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e, the interfacial area per unit area is more in Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs. The increase of planar defects will undoubtedly increase its hardness. Furthermore, as demonstrated by the XRD and TEM results, due to the reduced lattice constant (\u003cem\u003er\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e) of (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG compared to YAG, the lattice energy of (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG becomes higher according to the Born\u0026ndash;Land\u0026eacute; equation [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]:\u003cdiv id=\"Equd\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equd\" name=\"EquationSource\"\u003e\n$$\\begin{array}{c}{E}_{n}=-\\frac{{N}_{A}M{z}^{+}{z}^{-}{e}^{2}}{4\\pi {\\epsilon }_{0}{r}_{0}}\\left(1-\\frac{1}{n}\\right) \\#\\left(5\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003eN\u003c/em\u003e\u003csub\u003e\u003cem\u003eA\u003c/em\u003e\u003c/sub\u003e is Avogadro constant, \u003cem\u003eM\u003c/em\u003e is Madelung constant, \u003cem\u003ez\u003c/em\u003e\u003csup\u003e\u003cem\u003e+/\u0026minus;\u003c/em\u003e\u003c/sup\u003e is cationic/anion charge, \u003cem\u003eε\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e is vacuum permittivity (a constant), \u003cem\u003en\u003c/em\u003e is Born index (=\u0026thinsp;5\u0026thinsp;~\u0026thinsp;12), and \u003cem\u003er\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e is the distance between the nearest two ions. Therefore, the higher lattice bonding energy leads to higher hardness and elastic modulus of (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG. This is another pronounced reason for the improved hardness and elastic modulus of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs. In addition, since the introduction of the (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG, the interfacial structures are tailored, making ZrO\u003csub\u003e2\u003c/sub\u003e distribute finer and more dispersed. Fine ZrO\u003csub\u003e2\u003c/sub\u003e is distributed in both Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG, as well as between Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG, improving the fracture toughness of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs.\u003c/p\u003e \u003c/div\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eIn summary, Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs were successfully prepared by the directional solidification method. The ceramic was composed of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, the (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG and ZrO\u003csub\u003e2\u003c/sub\u003e phases. There was a lattice distortion in the (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG phase. The orientation relationship of the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs was determined to be [1-100] Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e || [100] ZrO\u003csub\u003e2\u003c/sub\u003e || [103] (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG, (11\u0026ndash;20) Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e || (020) ZrO\u003csub\u003e2\u003c/sub\u003e || (040) (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG, different from that of the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites. According to the NCSL model, the volume strain of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/ZrO\u003csub\u003e2\u003c/sub\u003e, Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG and ZrO\u003csub\u003e2\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG phases was 0.576%, 0.668% and \u0026minus;\u0026thinsp;0.604%, respectively. The values were comparable, unlike the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites where the volume strain of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG was an order of magnitude larger than the other two. As a result, ZrO\u003csub\u003e2\u003c/sub\u003e was mostly diffusely and uniformly distributed in Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs in the form of fine round rods. The hardness, elastic modulus, and fracture toughness of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs were significantly improved. This may be contributed to the solid solution (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG, which tailored the orientation relationships of the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs, redistributed ZrO\u003csub\u003e2\u003c/sub\u003e, refined the microstructure.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available from the corresponding author, Doc. Xu Wang, [email protected], upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contribution\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eXu Wang supervised the project. Yujie Zhong and Xu Wang designed the experiments. Zhe Li performed the experiments. All authors discussed experiments and results. Yujie Zhong wrote the draft. Yujie Zhong and Xu Wang revised the manuscript. All authors have given approval for the final version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the\u0026nbsp;National Natural Science Foundation of China\u0026nbsp;(grant numbers 52171046, 51804252), the Shaanxi Provincial Key Research and Development Program, China (No. 2021GY-133), and the Postgraduate Innovation and Practical Ability Training Program of Xi\u0026apos;an Shiyou University (No. YCS21212142).\u003c/p\u003e\n\u003cp\u003eConflict of interest \u0026nbsp;The authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eWilliams JC, Starke Jr EA (2003) Progress in structural materials for aerospace systems. 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Oxford university press. https://doi.org/10.1093/acprof:oso/9780199298815.001.0001\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"directional solidification, high-entropy oxide ceramic composites, eutectics, orientation relationship, interfacial structure","lastPublishedDoi":"10.21203/rs.3.rs-3137798/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3137798/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eA novel Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(Y\u003csub\u003e0.2\u003c/sub\u003eEr\u003csub\u003e0.2\u003c/sub\u003eYb\u003csub\u003e0.2\u003c/sub\u003eHo\u003csub\u003e0.2\u003c/sub\u003eLu\u003csub\u003e0.2\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003eAl\u003csub\u003e5\u003c/sub\u003eO\u003csub\u003e12\u003c/sub\u003e((5Re\u003csub\u003e0.2\u003c/sub\u003e)AG)/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic high entropy oxide ceramic composites (HEOCs) was prepared by the directional solidification technique. The Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs had a refined microstructure and different crystallographic orientation relationships of \u0026lt;\u0026thinsp;10\u0026ndash;10\u0026thinsp;\u0026gt;\u0026thinsp;Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e || \u0026lt;103\u0026gt;(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG || \u0026lt;100\u0026thinsp;\u0026gt;\u0026thinsp;ZrO\u003csub\u003e2\u003c/sub\u003e, {11\u0026ndash;20}Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e || {100}(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG || {100}ZrO\u003csub\u003e2\u003c/sub\u003e, {0001} Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e || {103}(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG || {100}ZrO\u003csub\u003e2\u003c/sub\u003e compared to Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites. ZrO\u003csub\u003e2\u003c/sub\u003e in the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic HEOCs was distributed more uniformly and dispersedly than in Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/YAG/ZrO\u003csub\u003e2\u003c/sub\u003e eutectic ceramic composites due to the similar volume strain of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/(5Re\u003csub\u003e0.2\u003c/sub\u003e)AG, (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG/ZrO\u003csub\u003e2\u003c/sub\u003e and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/ZrO\u003csub\u003e2\u003c/sub\u003e. As a result, mechanical performance including hardness, elastic modulus, and fracture toughness had been greatly improved because of the refined microstructure, tailored interfacial structure, and homogeneous distribution of ZrO\u003csub\u003e2\u003c/sub\u003e caused by the introduction of the high entropy (5Re\u003csub\u003e0.2\u003c/sub\u003e)AG.\u003c/p\u003e","manuscriptTitle":"Insight into tuning of ZrO2 distribution and mechanical properties of directionally solidified Al2O3/(5Re0.2)AG/ZrO2 eutectic ceramic composites","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-07-21 14:20:51","doi":"10.21203/rs.3.rs-3137798/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"8e740244-973c-45df-af98-8e27bdd40d7b","owner":[],"postedDate":"July 21st, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2023-07-25T08:44:29+00:00","versionOfRecord":[],"versionCreatedAt":"2023-07-21 14:20:51","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3137798","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3137798","identity":"rs-3137798","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}