A strategy for optimizing microstructure to simultaneously improve the strength and plasticity of W-Ni-Fe alloy

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To address this issue, we developed a novel approach combining in-situ freeze-drying and straightforward liquid-phase sintering techniques to effectively control the microstructure of 93W-4.9Ni-2.1Fe alloys. The corresponding W-Ni-Fe alloy in this work simultaneously takes into account ultrafine W-grains (28.3 µm), low W-W connectivity (Cw-w = 0.31) and suitable γ phase volume fraction (20.2%), which is currently difficult for traditional W-Ni-Fe alloys to achieve. The minute dimensions of nanopowder play a crucial role in inhibiting Ostwald ripening and facilitating W grain refinement. Additionally, the extensive surface area of nanopowder enhances capillary penetration, leading to effective homogenization of high γ phase volume. As a result, the freeze-dried W-Ni-Fe alloy simultaneously achieves high strength (1010 MPa) and high plasticity (31%), which provides a new insight for the further development of W-Ni-Fe alloy industries. Tungsten heavy alloys Freeze-drying Liquid phase sintering Ultrafine grains Low W-W connectivity Figures Figure 1 Figure 2 Figure 3 Figure 4 1 Introduction Tungsten heavy alloy (WHA) is a metal matrix composite material composed of tungsten and transition elements, including nickel, iron, cobalt and copper [ 1 , 2 ]. Among WHA, W-Ni-Fe alloy is widely used in aerospace, military and advanced manufacturing fields, such as kinetic energy piercing shell cores, missiles, electromagnetic guns and anti-X-ray shielding materials [ 3 , 4 ]. With the increasingly stringent service requirements of W-Ni-Fe alloys, low strength, and the strength/plasticity mismatch further limits the future development of W-Ni-Fe alloys [ 5 , 6 ]. In order to improve the strength of W-Ni-Fe alloys, current research mainly focuses on designing new compositions [ 7 ] and improving preparation processes [ 8 ]. The design of new components mainly refers to the addition of second phases (Y 2 O 3 , ZrC, etc. [ 9 , 10 ]) and the introduction of other solid solution elements (Mo, Re, etc. [ 11 , 12 ]). However, the second phase tends to agglomerate at the W/γ phase interface and become crack sources, thus deteriorating plasticity [ 13 ]. At the same time, introducing other solid solution elements (Mo, Re, etc.) can inhibit the dissolution of W in the γ phase, thereby reducing the γ phase volume fraction and then deteriorating plasticity [ 14 ]. On the other hand, improving preparation process mainly refers to adopting new sintering techniques (spark plasma sintering (SPS), hot isostatic pressing (HIP), additive manufacturing, etc. [ 15 – 17 ]) or conducting hot processing (rolling, forging, etc. [ 18 ]). The above new sintering techniques could help improve the strength and plasticity in some alloy systems such as Cu alloy [ 19 ], ODS steels [ 20 ], etc. However, the low solid phase sintering temperature (below the eutectic liquid point of 1465 ℃) and short-term insulation in W-Ni-Fe alloy system can help prepare ultrafine W grains and then improve strength, but it is not conducive to γ phase precipitation, γ phase network formation, and W particle spheroidization, which seriously deteriorates plasticity [ 21 ]. In addition, hot processing introduces a large number of dislocations in advance, which makes it difficult to continue storing a number of newly generated dislocations, thereby deteriorating plasticity [ 4 ]. It can be seen that traditional W-Ni-Fe alloys are difficult to simultaneously achieve high strength and high plasticity. Undoubtedly, it is urgent to simultaneously improve the strength and ductility of W-Ni-Fe alloy through optimizing powder preparation and supporting sintering processes. For sintering technology, although low-temperature sintering (< 1465 ℃) can refine grains and improve strength, it can lead to insufficient liquid phase, which affects γ phase precipitation, the network structure formation, and W particle spheroidization, ultimately resulting in poor plasticity [ 20 , 22 ]. The W particles in the liquid phase rapidly coarsen and destroy γ phase network during high-temperature sintering (> 1500 ℃), which is also not conducive to improving plasticity [ 23 ]. Therefore, the ideal sintering temperature range of W-Ni-Fe alloy is almost limited to the difficult to change range of 1465 ~ 1500 ℃. On this condition, the breakthrough point for improving the mechanical properties of W-Ni-Fe alloy should be the powder preparation process. Different powder preparation methods such as spray drying [ 24 ], chemical vapor deposition [ 25 ], sol-gel [ 26 ] and ball milling [ 23 ], possess significant impacts on final microstructure. Unfortunately, the alloy obtained by traditional powder preparation process is difficult to simultaneously achieve small spherical W particles, low W-W connectivity, and appropriate γ phase volume fraction [ 27 ], which is a severe challenge currently faced by W-Ni-Fe alloys. For example, the W-Ni-Fe alloy prepared by ball milling method has a high W-W connectivity, which deteriorates ductility (< 20%) [ 28 ], while the W-Ni-Fe alloy prepared by chemical method has a low γ phase volume fraction, resulting in low plasticity (< 20%) [ 26 ]. In our previous work, our research group utilized the advantages of freeze-drying to refine powders and improve powder uniformity, solving the second phase dispersion problem of pure W/Mo [ 29 ]. In this work, it is hoped that the dual phase alloy microstructure can be controlled by freeze-drying technology, ultimately improving the strength and plasticity of W-Ni-Fe alloy. In this study, the freeze-drying and liquid phase sintering techniques are employed to optimize W-Ni-Fe alloy structure, which combines ultrafine grain size, low W-W connectivity and suitable γ phase volume fraction. Corresponding, the freeze-dried W-Ni-Fe alloy simultaneously achieves high strength (1010 MPa) and high plasticity (31%). Furthermore, the potential strengthening and toughening mechanisms are systematically analysed. Details for the raw materials, experimental steps, and characterization details are provided in the Supplementary. The corresponding ball-milled (comparative sample) and freeze-dried W-Ni-Fe alloy were defined as BM sample and FD sample, respectively. 2 Experimental procedures 2.1 Raw materials The ammonium metatungstate (NH 4 ) 6 H 2 W 12 O 40 ·xH 2 O (AMT, Aladdin, 99.5%), nickel nitrate Ni(NO 3 ) 2 ·6H 2 O (Aladdin, 99.9%), ferric nitrate Fe(NO 3 ) 3 ·9H 2 O (Aladdin, 99.9%) and deionized water were chose as raw material. For comparison, commercially pure W (approximately 5 µm, 99.9%), Ni (1 ~ 2 µm, 99.9%), and Fe powder (1 ~ 2 µm, 99.9%) were selected. 2.2 Preparation details of powder and alloy Firstly, AMT, Ni(NO 3 ) 2 ·6H 2 O and Fe(NO 3 ) 3 ·9H 2 O were added into deionized water and fully dissolved to obtain a clear solution. Thereafter, the clarified solution was quickly pre frozen by low-temperature equipment (< -40℃), and next the collected pre-frozen solution were lyophilized to obtain loose precursor powder. After full grinding, the precursor powder was calcined at 500 ℃ for 30 min. The composite oxide powder was reduced at 600 ℃ and 850 ℃ for 120 min respectively in pure hydrogen atmosphere, thereby obtaining the final 93W-4.9Ni-2.1Fe composite powder. For comparison, ball milled 93W-4.9Ni-2.1Fe composite powder (300 r/min, 5 h) was used as a reference powder. Finally, above two composite powders were pressed into diameter billets and sintered at 1480°C for 1.5 h in a hydrogen atmosphere to obtain 93W-4.9Ni-2.1Fe alloy. 2.3 Mechanical properties test The Vickers microhardness was performed at a load of 200 gf and a dwell time of 15 s. Each specimen was tested 20 times to obtain an average value. The tensile specimens were tested at room temperature on an Instron 5982 testing machine at a strain rate of 0.001 s − 1 .The working length is 5 mm, the cross-section size is 1.5 × 1.0 mm 2 , and the transition arc diameter is 1.25 mm. 2.4 Structural characterization The Archimedes method was employed to measure the density of sintered samples. The phase compositions of samples were analyzed by X-ray diffraction (XRD, D/MAX-2500). The morphological characteristics of the powders and alloys were observed using a scanning electron microscope (SEM, Hitachi Model No. S4800) equipped with an energy dispersive spectrometer (EDS) and a transmission electron microscope (TEM, JEM-2100). To better present the alloy morphology after tensile fracture, the alloy was mechanically polished before tensile testing. The crack distribution near the fracture surface was directly observed using a scanning electron microscope (SEM, JSM-7800F). 3 Results and Discussion Figure 1 a ~ 1b represent the typical morphology of W-Ni-Fe powder fabricated by freeze drying and ball-milling, and the corresponding average grain size is 202 ± 69 nm and 2.13 ± 1.01 µm (see Fig. 1 c), respectively. On the other hand, the freeze-dried W-Ni-Fe powder possesses W and γ-(Ni, Fe) phases (see Fig. 1 d ~ 1e), which indicates that freeze-drying technology achieves complete solid solution of Ni and Fe elements with W. By comparison, the W, Ni and Fe powders were only simply mixed via ball milling and did not produce new γ-(Ni, Fe) phase, which is not conducive to improve the γ phase dispersion in subsequent sintered alloys. Such uniformly composed and ultrafine freeze-dried W-Ni-Fe powder can be attributed to its special powder preparation process. When the water starts to rapidly freeze, the ice nuclei formed instantly consume nearby water, thereby creating a number of solid-liquid interfaces[ 30 ]. The rapid cooling promotes the solid-liquid interface migration velocity to exceed the solute diffusion velocity [ 31 ]. Therefore, solutes are confined to their original positions and in-situ precipitate during subsequent freeze-drying process, ensuring the refinement, dispersion and doping uniformity [ 32 ]. In particular, the above characteristics of nanopowder is conducive to optimize microstructure during subsequent sintering process. Indeed, the nanopowder with elevated activation energy could preferentially form sintered neck in early sintering stage [ 33 ], accelerate densification process via shortening the material migration path [ 34 ], and restrain Ostwald ripening during liquid phase sintering [ 35 ], resulting in the accelerated densification and grain refinement. After subsequent sintering, both alloys are composed of W and γ phases, as exhibited in Fig. 1 d ~ 1e. Figures 2 a and 2 b display the representative morphology of sintered FD alloy ( 28.3 ± 11.9 µm) and BM alloy (34.7 ± 14.1 µm), which confirms the advantages of above ultrafine W-Ni-Fe powders. As shown in Figs. 2 c, the relative density of the FD alloys is 99.2%, while the relative density of BM sample is only 95.0%. Compared with BM W-Ni-Fe powders, the prepared FD nanopowders exhibit favorable sintering drive and small composite scales, which helps to shorten the material migration path and enhance density [ 23 ]. On the other hand, the γ phase volume fraction/ W-W connectivity of FD alloy and BM alloy is 20.0%/0.31 and 12.2%/0.44, respectively. The corresponding γ phase of FD alloy possess lower W-W connectivity and better network like structure compared to BM alloy, which helps improve strength and plasticity. The high W content and similar Ni/Fe ratio into γ phase (see Fig. 2 d) incicates that the high γ phase volume fraction of FD alloy originates from high W solid solubility. According to the actual service conditions of W-Ni-Fe alloy, room temperature tensile properties and hardness are the most representative. As exhibited in Fig. 3 a, the FD alloy has excellent tensile properties (1010 ± 6 MPa, 31.5 ± 0.5%), while the BM alloy exhibits lower tensile properties (920 ± 7 MPa, 24.6 ± 0.6%). As exhibited in Fig. 3 b, the corresponding Vickers hardness of FD alloy and BM alloy is 366 ± 18 HV 0.2 and 377 ± 16 HV 0.2 respectively. By comparison, FD alloy combines high tensile strength, high hardness and excellent plasticity. Figure 3 c lists the relevant tensile properties of 93W-Ni-Fe alloy reported in literatures. Thus one can see that the traditional 93W-Ni-Fe alloy usually possess poor plasticity ( 1000 MPa), and its strength is usually low ( 30%). Fortunately, the strength and ductility of the W-Ni-Fe alloy prepared in this work are excellently matched. Such excellent mechanical properties are closely related to alloy microstructure. However, it includes many variables, including W particle size, W-W connectivity (W distribution uniformity), γ phase volume fraction, W-γ phase interface width, etc. Up to now, there is a lack of systematic research on how microstructure affects mechanical properties. Firstly, the changes to a single variable are discussed. When the W particle size decreases, the small W particles are better anchored and store dislocations as a whole, and both strength and plasticity will be improved [ 34 ]. When the W-W connectivity decreases (W dispersion increases), it promotes the network structure formation, reduces strength, and improves plasticity [ 2 ]. It is not conducive to the network structure formation when the γ phase volume fraction is too small, and the W particles will settle when the γ phase volume fraction is too large [ 36 ]. Therefore, an appropriate volume fraction of the network γ phase is beneficial for improving strength and plasticity [ 6 ]. Within the appropriate γ phase volume fraction range, the high W content into γ phase could result in limited work hardening effect (usually < 20 MPa [ 37 ]), but the increasing γ phase after increasing W content is beneficial for improving significantly plasticity. In addition, the thicker interface width provides better resistance to crack initiation, thereby enhancing strength and plasticity [ 38 ]. From the perspective of preparation process, SPS [ 20 ], HIP [ 17 ], additive manufacturing [ 42 ] and other processes involving rapid heating and short-term insulation, as well as traditional solid phase sintering (< 1465 ℃) process, are difficult to generate a number of γ phase and construct uniform network structure, which inevitably leads to serious deterioration of plasticity (see Fig. 3 c). It can be seen that it is necessary to maintain insulation above liquid phase sintering temperature (> 1465 ℃) for a long time to improve plasticity. In this situation, the strength of W/γ interface minimally affected (1). Next, after limiting the liquid-phase sintering of W-Ni-Fe alloy, Fig. 3 d displays the three-dimensional relationship between tensile properties and microstructure including W particle size (d), W-W connectivity (C W−W ), γ phase volume fraction (V M ), and Figs. 3 e ~ 3f depicts related V M -d and V M -C W−W two-dimensional images. The corresponding results are divided into three regions: blue region (low γ phase), purple region (high W-W connectivity), and orange region (coarse W grains). After comparison, one can see that in the blue region, W-Ni-Fe alloy with ultrafine W grains exhibits poor strength and ductility due to its low γ phase volume fraction. In the orange region, The W-Ni-Fe alloy with high γ phase volume possesses coarse grains, which is not conducive to improving strength and ductility. For purple region, although the grain size and γ phase volume fraction are moderate, the W-W connectivity is high, which is not conducive to improving plasticity. It is particularly noteworthy that the freeze-dried W-Ni-Fe alloy in this work possess ultra low W-W connectivity, which may sacrifice strength but significantly improve plasticity, and can greatly enhance the sacrificed strength through grain refinement, thereby achieving a perfect match between strength and plasticity. The tensile specimen fracture morphology is further analysed, as exhibited in Fig. 4 a ~ 4b. The fracture morphology includes four modes: W cleavage (WC), W-W intergranular fracture (WF), matrix γ phase rupture (γR) and W-matrix γ phase interfacial separation (W/γD) [ 2 , 18 , 47 ]. According to the statistical results (see Fig. 4 c), the FD alloy proportions of WC, WF, γR and W/γD are 50%, 14%, 25%, and 11% respectively, while the BM alloy proportions of WC, WF, γR and W/γD are 34%, 34%, 26%, and 6% respectively. In contrast, the main difference is that the WC proportion of FD alloy has significantly increased, while the WF proportion has sharply decreased. Among the four common fracture modes mentioned above, WF has the lowest strength [ 48 , 49 ], so that cracks often originate between W-W grains. Compared to BM alloy, FD alloy possesses dispersed small W grains and less W-W interface proportion, resulting in a significant decrease in the proportion of crack initiation and propagation along W-W grain boundary. This explains its high proportion of W dissociation and indirectly confirms its high strength. Accompanied by further deformation, the dislocation density stored within γ phase increases significantly, and cracks continue to propagate at the W-W grain boundary or W/γ phase interface. At this stage, FD alloy with high γ phase volume will trigger a unique crack bridging mechanism in γ phase [ 2 , 23 ]. When the crack extends along W/W or W/γ, the γ phase will cross both sides of crack like a micro bridge (Fig. 4 d), significantly delaying the material fracture process (thus improving plasticity) by continuously transferring the load and passivating the crack [ 5 ]. During final necking stage, cracks propagate into γ phase interior, ultimately leading to failure. In contrast, BM alloy has a lower γ phase volume fraction, which makes it difficult to transfer loads and bridge cracks(Fig. 4 e). At the same time, cracks tend to propagate along the W-W grain boundaries or W/γ phase boundaries, which are not conducive to improving plasticity. 4 Conclusions In summary, our work reports a novel freeze-drying and liquid phase sintering technique to optimize microstructure of W-Ni-Fe alloy. Results show that the ultrafine size of nanopowder helps to restrain Ostwald ripening and achieve W grain refinement. And the high surface of nanopowder can better drive capillary penetration and realize the homogenization of high γ phase volume. Therefore, the W-Ni-Fe alloy simultaneously combines ultrafine W grains (28.3 µm), low W-W connectivity (Cw-w = 0.31) and suitable γ phase volume fraction (20.2%), thus overcoming the difficulty that traditional W-Ni-Fe alloys cannot simultaneously achieve the above factors. These factors lead to a perfect match between the strength (1010 MPa) and plasticity (31%), which will shed light on the further development for two phase alloy systems similar to W-Ni-Fe alloy. Declarations Conflict of interest The authors declare no competing interests. Funding This work is supported by Key Laboratory of Advanced Structural Materials (Changchun University of Technology), Ministry of Education, China (Grant No. ASM-202404). This work is supported by National Natural Science Foundation of China (Grant No. 52122409), The Open Research Fund of Suzhou Laboratory (Grant No. SZLAB-1108-2024-ZD003), Beijing Natural Science Foundation (Grant No. L241037), Tianjin Natural Science Foundation (Grant No. 24JCZDJC01160) and Science and Technology Program of Tianjin (Grant No.23ZGSSSS00050). Author Contribution Chongji Wu: Investigation, Methodology, Formal analysis, Validation, Writing - Original Draft.Lu Yang: Conceptualization, Validation.Zhu Qian: Formal analysis, Methodology.Zupeng Yan: Formal analysis.Xia Sun: Supervision.Weiqiang Hu: Conceptualization, Methodology, Supervision.Zongqing Ma: Conceptualization, Validation, Supervision.All authors reviewed the manuscript. Data availability The data used to support the findings of this study are available from the corresponding author upon request. References X. Liu, J.P. Wu, K.K. Qiao, G.H. Liu, Z.J. Wang, T.Q. Lu, Z.G. Suo, J. Hu, Topoarchitected polymer networks expand the space of material properties, Nat. Commun. 13 (2022) 1622. M.E. Alam, G.R. Odette, On the remarkable fracture toughness of 90 to 97W-NiFe alloys revealing powerful new ductile phase toughening mechanisms, Acta Mater. 186 (2020) 324-340. U. Ravi Kiran, A. Panchal, M. Sankaranarayana, G.V.S. Nageswara Rao, T.K. 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Res. 15-17 (2006) 575-580. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 16 Oct, 2025 Read the published version in Advanced Composites and Hybrid Materials → Version 1 posted Editorial decision: Revision requested 10 Aug, 2025 Reviews received at journal 08 Aug, 2025 Reviews received at journal 01 Aug, 2025 Reviewers agreed at journal 30 Jul, 2025 Reviewers agreed at journal 23 Jul, 2025 Reviewers agreed at journal 21 Jul, 2025 Reviews received at journal 20 Jul, 2025 Reviewers agreed at journal 14 Jul, 2025 Reviewers agreed at journal 14 Jul, 2025 Reviewers invited by journal 14 Jul, 2025 Editor assigned by journal 12 Jul, 2025 Submission checks completed at journal 06 Jul, 2025 First submitted to journal 04 Jul, 2025 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. 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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-7043710","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":485447549,"identity":"0c9dfb07-1410-414d-ac0c-d9b9b63d3c5e","order_by":0,"name":"Chongji Wu","email":"","orcid":"","institution":"Tianjin University","correspondingAuthor":false,"prefix":"","firstName":"Chongji","middleName":"","lastName":"Wu","suffix":""},{"id":485447551,"identity":"ac33718a-40cd-4e27-962b-2a15bca8e60d","order_by":1,"name":"Lu Yang","email":"","orcid":"","institution":"Henan University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Lu","middleName":"","lastName":"Yang","suffix":""},{"id":485447553,"identity":"b83f16db-f964-41a2-9b8b-2446b5d9634f","order_by":2,"name":"Zhu Qian","email":"","orcid":"","institution":"Tianjin Zhujin Technology Development Corporation","correspondingAuthor":false,"prefix":"","firstName":"Zhu","middleName":"","lastName":"Qian","suffix":""},{"id":485447556,"identity":"51af7c5b-f066-4703-90c1-a9393b1f1606","order_by":3,"name":"Zupeng Yan","email":"","orcid":"","institution":"Tianjin Zhujin Technology Development Corporation","correspondingAuthor":false,"prefix":"","firstName":"Zupeng","middleName":"","lastName":"Yan","suffix":""},{"id":485447557,"identity":"3ce9ef79-58ea-4f3a-8361-d600d8b88dab","order_by":4,"name":"Xia Sun","email":"","orcid":"","institution":"Tianjin Zhujin Technology Development Corporation","correspondingAuthor":false,"prefix":"","firstName":"Xia","middleName":"","lastName":"Sun","suffix":""},{"id":485447558,"identity":"6a69a0b2-3856-4ceb-99f5-4181df3d1600","order_by":5,"name":"Weiqiang Hu","email":"","orcid":"","institution":"Tianjin University","correspondingAuthor":false,"prefix":"","firstName":"Weiqiang","middleName":"","lastName":"Hu","suffix":""},{"id":485447559,"identity":"5b72830b-e4e9-448f-930b-5a85a1469a99","order_by":6,"name":"Zongqing Ma","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAu0lEQVRIiWNgGAWjYJCCgx8qJOTY2NsPEK2D8bHEGRtjPp4zCURrYTbgbUtLnCfhYECcet3+w9skJNgOp7dJMCQw/KjYRliL2YFjZRIFPIdz26QbDzD2nLlNhJaDPWYSEhJALTIHEpgZ24jRcpjHTILH4HA6m0SCAZFajvEYG/AkpCWQoOUMW+FjiQM2hm3AQD5InF/OH95w8OM/CXn59vaDD35UEKEFCBDRcYAo9ShaRsEoGAWjYBRgBQDM7TxoyK3XuQAAAABJRU5ErkJggg==","orcid":"","institution":"Tianjin University","correspondingAuthor":true,"prefix":"","firstName":"Zongqing","middleName":"","lastName":"Ma","suffix":""}],"badges":[],"createdAt":"2025-07-04 06:53:05","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7043710/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7043710/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s42114-025-01475-y","type":"published","date":"2025-10-16T15:58:13+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":86842481,"identity":"60ae5bf2-71da-4f3a-a469-d1dbf78cc6af","added_by":"auto","created_at":"2025-07-16 08:15:15","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":984694,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea-b\u003c/strong\u003eTEM image of W-Ni-Fe composite powders fabricated by freeze-drying and ball-milling; \u003cstrong\u003ec\u003c/strong\u003e Average grain size distribution of freeze-dried and ball-milled powders; \u003cstrong\u003ed\u003c/strong\u003e XRD patterns of W-Ni-Fe composite powders and sintered alloys; \u003cstrong\u003ee\u003c/strong\u003e corresponding enlarged XRD patterns.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7043710/v1/24a05eefac54ffe1f6568153.png"},{"id":86842483,"identity":"44855954-338b-4bd4-b73a-c519736e3806","added_by":"auto","created_at":"2025-07-16 08:15:15","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":169975,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea \u003c/strong\u003eand \u003cstrong\u003eb\u003c/strong\u003e SEM image of specimens fabricated by freeze-drying and ball-milling; \u003cstrong\u003ec\u003c/strong\u003e The corresponding W content and Ni/Fe ratio in γ phase; \u003cstrong\u003ed\u003c/strong\u003e The corresponding grain size and relative density.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7043710/v1/ca3de30aa995fb43c6108c85.png"},{"id":86842485,"identity":"dadae9b5-11df-4d66-b655-e904d071dab5","added_by":"auto","created_at":"2025-07-16 08:15:15","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1583650,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e Tensile stress-strain curves of FD and BM specimens; \u003cstrong\u003eb\u003c/strong\u003e The corresponding microhardness, ultimate tensile strength and ultimate elongation specimens; \u003cstrong\u003ec\u003c/strong\u003e The tensile properties of 93W-Ni-Fe alloys prepared in this work are compared with those 93W-Ni-Fe alloys reported in the literatures[2, 21, 39-46], including liquid phase sintering (LPS), additive manufacturing (AM), hot isostatic pressing (HIP), and spark plasma sintering (SPS); The \u0026nbsp;relationship between 93W-Ni-Fe alloy tensile properties and liquid-phase sintering (LPS) microstructure, including γ phase volume fraction (V\u003csub\u003eM\u003c/sub\u003e), W-W contiguity (C\u003csub\u003eW-W\u003c/sub\u003e) [2, 21, 39-41], \u003cstrong\u003ed\u003c/strong\u003e 3D image of V\u003csub\u003eM\u003c/sub\u003e-C\u003csub\u003eW-W\u003c/sub\u003e-d , 2D images of \u003cstrong\u003ee\u003c/strong\u003e V\u003csub\u003eM\u003c/sub\u003e-d , \u003cstrong\u003ef\u003c/strong\u003e V\u003csub\u003eM\u003c/sub\u003e-C\u003csub\u003eW-W\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-7043710/v1/1dbf3cbdcb577c8ccb3d2319.png"},{"id":86842484,"identity":"feee59cf-2766-4925-8026-6058b8c98e93","added_by":"auto","created_at":"2025-07-16 08:15:15","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":273490,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea-b\u003c/strong\u003eTensile fracture morphology of specimens showing the four basic fracture modes: W cleavage (WC), W-W intergranular fracture (WF), matrix γ phase rupture (γR) and W-matrix γ phase interfacial separation (W/γD); \u003cstrong\u003ec\u003c/strong\u003e The statistical ratios of four basic fracture modes; \u003cstrong\u003ed-f \u003c/strong\u003eBSE images of tensile fracture side of specimens.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7043710/v1/9aa1bda361043c16e0b12ebe.png"},{"id":93956154,"identity":"04e6d5c3-0d5e-4f17-a7d4-feca36ed42b2","added_by":"auto","created_at":"2025-10-20 16:11:15","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3499577,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7043710/v1/08fab401-31b3-4fc5-a5a8-1165c43dbb2a.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"A strategy for optimizing microstructure to simultaneously improve the strength and plasticity of W-Ni-Fe alloy","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eTungsten heavy alloy (WHA) is a metal matrix composite material composed of tungsten and transition elements, including nickel, iron, cobalt and copper [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Among WHA, W-Ni-Fe alloy is widely used in aerospace, military and advanced manufacturing fields, such as kinetic energy piercing shell cores, missiles, electromagnetic guns and anti-X-ray shielding materials [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. With the increasingly stringent service requirements of W-Ni-Fe alloys, low strength, and the strength/plasticity mismatch further limits the future development of W-Ni-Fe alloys [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn order to improve the strength of W-Ni-Fe alloys, current research mainly focuses on designing new compositions [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] and improving preparation processes [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. The design of new components mainly refers to the addition of second phases (Y\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, ZrC, etc. [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]) and the introduction of other solid solution elements (Mo, Re, etc. [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]). However, the second phase tends to agglomerate at the W/γ phase interface and become crack sources, thus deteriorating plasticity [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. At the same time, introducing other solid solution elements (Mo, Re, etc.) can inhibit the dissolution of W in the γ phase, thereby reducing the γ phase volume fraction and then deteriorating plasticity [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. On the other hand, improving preparation process mainly refers to adopting new sintering techniques (spark plasma sintering (SPS), hot isostatic pressing (HIP), additive manufacturing, etc. [\u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]) or conducting hot processing (rolling, forging, etc. [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]). The above new sintering techniques could help improve the strength and plasticity in some alloy systems such as Cu alloy [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], ODS steels [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], etc. However, the low solid phase sintering temperature (below the eutectic liquid point of 1465 ℃) and short-term insulation in W-Ni-Fe alloy system can help prepare ultrafine W grains and then improve strength, but it is not conducive to γ phase precipitation, γ phase network formation, and W particle spheroidization, which seriously deteriorates plasticity [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. In addition, hot processing introduces a large number of dislocations in advance, which makes it difficult to continue storing a number of newly generated dislocations, thereby deteriorating plasticity [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. It can be seen that traditional W-Ni-Fe alloys are difficult to simultaneously achieve high strength and high plasticity.\u003c/p\u003e\u003cp\u003eUndoubtedly, it is urgent to simultaneously improve the strength and ductility of W-Ni-Fe alloy through optimizing powder preparation and supporting sintering processes. For sintering technology, although low-temperature sintering (\u0026lt;\u0026thinsp;1465 ℃) can refine grains and improve strength, it can lead to insufficient liquid phase, which affects γ phase precipitation, the network structure formation, and W particle spheroidization, ultimately resulting in poor plasticity [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. The W particles in the liquid phase rapidly coarsen and destroy γ phase network during high-temperature sintering (\u0026gt;\u0026thinsp;1500 ℃), which is also not conducive to improving plasticity [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Therefore, the ideal sintering temperature range of W-Ni-Fe alloy is almost limited to the difficult to change range of 1465\u0026thinsp;~\u0026thinsp;1500 ℃. On this condition, the breakthrough point for improving the mechanical properties of W-Ni-Fe alloy should be the powder preparation process.\u003c/p\u003e\u003cp\u003eDifferent powder preparation methods such as spray drying [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], chemical vapor deposition [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e], sol-gel [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] and ball milling [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], possess significant impacts on final microstructure. Unfortunately, the alloy obtained by traditional powder preparation process is difficult to simultaneously achieve small spherical W particles, low W-W connectivity, and appropriate γ phase volume fraction [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], which is a severe challenge currently faced by W-Ni-Fe alloys. For example, the W-Ni-Fe alloy prepared by ball milling method has a high W-W connectivity, which deteriorates ductility (\u0026lt;\u0026thinsp;20%) [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], while the W-Ni-Fe alloy prepared by chemical method has a low γ phase volume fraction, resulting in low plasticity (\u0026lt;\u0026thinsp;20%) [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. In our previous work, our research group utilized the advantages of freeze-drying to refine powders and improve powder uniformity, solving the second phase dispersion problem of pure W/Mo [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. In this work, it is hoped that the dual phase alloy microstructure can be controlled by freeze-drying technology, ultimately improving the strength and plasticity of W-Ni-Fe alloy.\u003c/p\u003e\u003cp\u003eIn this study, the freeze-drying and liquid phase sintering techniques are employed to optimize W-Ni-Fe alloy structure, which combines ultrafine grain size, low W-W connectivity and suitable γ phase volume fraction. Corresponding, the freeze-dried W-Ni-Fe alloy simultaneously achieves high strength (1010 MPa) and high plasticity (31%). Furthermore, the potential strengthening and toughening mechanisms are systematically analysed.\u003c/p\u003e\u003cp\u003eDetails for the raw materials, experimental steps, and characterization details are provided in the Supplementary. The corresponding ball-milled (comparative sample) and freeze-dried W-Ni-Fe alloy were defined as BM sample and FD sample, respectively.\u003c/p\u003e"},{"header":"2 Experimental procedures","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Raw materials\u003c/h2\u003e\u003cp\u003eThe ammonium metatungstate (NH\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eW\u003csub\u003e12\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e\u0026middot;xH\u003csub\u003e2\u003c/sub\u003eO (AMT, Aladdin, 99.5%), nickel nitrate Ni(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO (Aladdin, 99.9%), ferric nitrate Fe(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;9H\u003csub\u003e2\u003c/sub\u003eO (Aladdin, 99.9%) and deionized water were chose as raw material. For comparison, commercially pure W (approximately 5 \u0026micro;m, 99.9%), Ni (1\u0026thinsp;~\u0026thinsp;2 \u0026micro;m, 99.9%), and Fe powder (1\u0026thinsp;~\u0026thinsp;2 \u0026micro;m, 99.9%) were selected.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e\u003cb\u003e2.2 Preparation details of powder and alloy\u003c/b\u003e\u003c/h2\u003e\u003cp\u003eFirstly, AMT, Ni(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO and Fe(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;9H\u003csub\u003e2\u003c/sub\u003eO were added into deionized water and fully dissolved to obtain a clear solution. Thereafter, the clarified solution was quickly pre frozen by low-temperature equipment (\u0026lt; -40℃), and next the collected pre-frozen solution were lyophilized to obtain loose precursor powder. After full grinding, the precursor powder was calcined at 500 ℃ for 30 min. The composite oxide powder was reduced at 600 ℃ and 850 ℃ for 120 min respectively in pure hydrogen atmosphere, thereby obtaining the final 93W-4.9Ni-2.1Fe composite powder. For comparison, ball milled 93W-4.9Ni-2.1Fe composite powder (300 r/min, 5 h) was used as a reference powder. Finally, above two composite powders were pressed into diameter billets and sintered at 1480\u0026deg;C for 1.5 h in a hydrogen atmosphere to obtain 93W-4.9Ni-2.1Fe alloy.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Mechanical properties test\u003c/h2\u003e\u003cp\u003eThe Vickers microhardness was performed at a load of 200 gf and a dwell time of 15 s. Each specimen was tested 20 times to obtain an average value. The tensile specimens were tested at room temperature on an Instron 5982 testing machine at a strain rate of 0.001 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.The working length is 5 mm, the cross-section size is 1.5 \u0026times; 1.0 mm\u003csup\u003e2\u003c/sup\u003e, and the transition arc diameter is 1.25 mm.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4 Structural characterization\u003c/h2\u003e\u003cp\u003eThe Archimedes method was employed to measure the density of sintered samples. The phase compositions of samples were analyzed by X-ray diffraction (XRD, D/MAX-2500). The morphological characteristics of the powders and alloys were observed using a scanning electron microscope (SEM, Hitachi Model No. S4800) equipped with an energy dispersive spectrometer (EDS) and a transmission electron microscope (TEM, JEM-2100). To better present the alloy morphology after tensile fracture, the alloy was mechanically polished before tensile testing. The crack distribution near the fracture surface was directly observed using a scanning electron microscope (SEM, JSM-7800F).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"3 Results and Discussion","content":"\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea\u0026thinsp;~\u0026thinsp;1b represent the typical morphology of W-Ni-Fe powder fabricated by freeze drying and ball-milling, and the corresponding average grain size is 202\u0026thinsp;\u0026plusmn;\u0026thinsp;69 nm and 2.13\u0026thinsp;\u0026plusmn;\u0026thinsp;1.01 \u0026micro;m (see Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec), respectively. On the other hand, the freeze-dried W-Ni-Fe powder possesses W and γ-(Ni, Fe) phases (see Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed\u0026thinsp;~\u0026thinsp;1e), which indicates that freeze-drying technology achieves complete solid solution of Ni and Fe elements with W. By comparison, the W, Ni and Fe powders were only simply mixed via ball milling and did not produce new γ-(Ni, Fe) phase, which is not conducive to improve the γ phase dispersion in subsequent sintered alloys. Such uniformly composed and ultrafine freeze-dried W-Ni-Fe powder can be attributed to its special powder preparation process. When the water starts to rapidly freeze, the ice nuclei formed instantly consume nearby water, thereby creating a number of solid-liquid interfaces[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. The rapid cooling promotes the solid-liquid interface migration velocity to exceed the solute diffusion velocity [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. Therefore, solutes are confined to their original positions and in-situ precipitate during subsequent freeze-drying process, ensuring the refinement, dispersion and doping uniformity [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. In particular, the above characteristics of nanopowder is conducive to optimize microstructure during subsequent sintering process. Indeed, the nanopowder with elevated activation energy could preferentially form sintered neck in early sintering stage [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e], accelerate densification process via shortening the material migration path [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e], and restrain Ostwald ripening during liquid phase sintering [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e], resulting in the accelerated densification and grain refinement.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAfter subsequent sintering, both alloys are composed of W and γ phases, as exhibited in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed\u0026thinsp;~\u0026thinsp;1e. Figures\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb display the representative morphology of sintered FD alloy ( 28.3\u0026thinsp;\u0026plusmn;\u0026thinsp;11.9 \u0026micro;m) and BM alloy (34.7\u0026thinsp;\u0026plusmn;\u0026thinsp;14.1 \u0026micro;m), which confirms the advantages of above ultrafine W-Ni-Fe powders. As shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec, the relative density of the FD alloys is 99.2%, while the relative density of BM sample is only 95.0%. Compared with BM W-Ni-Fe powders, the prepared FD nanopowders exhibit favorable sintering drive and small composite scales, which helps to shorten the material migration path and enhance density [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. On the other hand, the γ phase volume fraction/ W-W connectivity of FD alloy and BM alloy is 20.0%/0.31 and 12.2%/0.44, respectively. The corresponding γ phase of FD alloy possess lower W-W connectivity and better network like structure compared to BM alloy, which helps improve strength and plasticity. The high W content and similar Ni/Fe ratio into γ phase (see Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed) incicates that the high γ phase volume fraction of FD alloy originates from high W solid solubility.\u003c/p\u003e\u003cp\u003eAccording to the actual service conditions of W-Ni-Fe alloy, room temperature tensile properties and hardness are the most representative. As exhibited in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, the FD alloy has excellent tensile properties (1010\u0026thinsp;\u0026plusmn;\u0026thinsp;6 MPa, 31.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5%), while the BM alloy exhibits lower tensile properties (920\u0026thinsp;\u0026plusmn;\u0026thinsp;7 MPa, 24.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6%). As exhibited in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb, the corresponding Vickers hardness of FD alloy and BM alloy is 366\u0026thinsp;\u0026plusmn;\u0026thinsp;18 HV\u003csub\u003e0.2\u003c/sub\u003e and 377\u0026thinsp;\u0026plusmn;\u0026thinsp;16 HV\u003csub\u003e0.2\u003c/sub\u003e respectively. By comparison, FD alloy combines high tensile strength, high hardness and excellent plasticity. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec lists the relevant tensile properties of 93W-Ni-Fe alloy reported in literatures. Thus one can see that the traditional 93W-Ni-Fe alloy usually possess poor plasticity (\u0026lt;\u0026thinsp;22%) when its strength is high (\u0026gt;\u0026thinsp;1000 MPa), and its strength is usually low (\u0026lt;\u0026thinsp;950 MPa) when its plasticity is high (\u0026gt;\u0026thinsp;30%). Fortunately, the strength and ductility of the W-Ni-Fe alloy prepared in this work are excellently matched.\u003c/p\u003e\u003cp\u003eSuch excellent mechanical properties are closely related to alloy microstructure. However, it includes many variables, including W particle size, W-W connectivity (W distribution uniformity), γ phase volume fraction, W-γ phase interface width, etc. Up to now, there is a lack of systematic research on how microstructure affects mechanical properties. Firstly, the changes to a single variable are discussed. When the W particle size decreases, the small W particles are better anchored and store dislocations as a whole, and both strength and plasticity will be improved [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. When the W-W connectivity decreases (W dispersion increases), it promotes the network structure formation, reduces strength, and improves plasticity [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. It is not conducive to the network structure formation when the γ phase volume fraction is too small, and the W particles will settle when the γ phase volume fraction is too large [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. Therefore, an appropriate volume fraction of the network γ phase is beneficial for improving strength and plasticity [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Within the appropriate γ phase volume fraction range, the high W content into γ phase could result in limited work hardening effect (usually\u0026thinsp;\u0026lt;\u0026thinsp;20 MPa [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]), but the increasing γ phase after increasing W content is beneficial for improving significantly plasticity. In addition, the thicker interface width provides better resistance to crack initiation, thereby enhancing strength and plasticity [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFrom the perspective of preparation process, SPS [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], HIP [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], additive manufacturing [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e] and other processes involving rapid heating and short-term insulation, as well as traditional solid phase sintering (\u0026lt;\u0026thinsp;1465 ℃) process, are difficult to generate a number of γ phase and construct uniform network structure, which inevitably leads to serious deterioration of plasticity (see Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). It can be seen that it is necessary to maintain insulation above liquid phase sintering temperature (\u0026gt;\u0026thinsp;1465 ℃) for a long time to improve plasticity. In this situation, the strength of W/γ interface minimally affected (1). Next, after limiting the liquid-phase sintering of W-Ni-Fe alloy, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed displays the three-dimensional relationship between tensile properties and microstructure including W particle size (d), W-W connectivity (C\u003csub\u003eW\u0026minus;W\u003c/sub\u003e), γ phase volume fraction (V\u003csub\u003eM\u003c/sub\u003e), and Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee\u0026thinsp;~\u0026thinsp;3f depicts related V\u003csub\u003eM\u003c/sub\u003e-d and V\u003csub\u003eM\u003c/sub\u003e-C\u003csub\u003eW\u0026minus;W\u003c/sub\u003e two-dimensional images. The corresponding results are divided into three regions: blue region (low γ phase), purple region (high W-W connectivity), and orange region (coarse W grains). After comparison, one can see that in the blue region, W-Ni-Fe alloy with ultrafine W grains exhibits poor strength and ductility due to its low γ phase volume fraction. In the orange region, The W-Ni-Fe alloy with high γ phase volume possesses coarse grains, which is not conducive to improving strength and ductility. For purple region, although the grain size and γ phase volume fraction are moderate, the W-W connectivity is high, which is not conducive to improving plasticity. It is particularly noteworthy that the freeze-dried W-Ni-Fe alloy in this work possess ultra low W-W connectivity, which may sacrifice strength but significantly improve plasticity, and can greatly enhance the sacrificed strength through grain refinement, thereby achieving a perfect match between strength and plasticity.\u003c/p\u003e\u003cp\u003eThe tensile specimen fracture morphology is further analysed, as exhibited in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea\u0026thinsp;~\u0026thinsp;4b. The fracture morphology includes four modes: W cleavage (WC), W-W intergranular fracture (WF), matrix γ phase rupture (γR) and W-matrix γ phase interfacial separation (W/γD) [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]. According to the statistical results (see Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec), the FD alloy proportions of WC, WF, γR and W/γD are 50%, 14%, 25%, and 11% respectively, while the BM alloy proportions of WC, WF, γR and W/γD are 34%, 34%, 26%, and 6% respectively. In contrast, the main difference is that the WC proportion of FD alloy has significantly increased, while the WF proportion has sharply decreased. Among the four common fracture modes mentioned above, WF has the lowest strength [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e], so that cracks often originate between W-W grains. Compared to BM alloy, FD alloy possesses dispersed small W grains and less W-W interface proportion, resulting in a significant decrease in the proportion of crack initiation and propagation along W-W grain boundary. This explains its high proportion of W dissociation and indirectly confirms its high strength.\u003c/p\u003e\u003cp\u003eAccompanied by further deformation, the dislocation density stored within γ phase increases significantly, and cracks continue to propagate at the W-W grain boundary or W/γ phase interface. At this stage, FD alloy with high γ phase volume will trigger a unique crack bridging mechanism in γ phase [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. When the crack extends along W/W or W/γ, the γ phase will cross both sides of crack like a micro bridge (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed), significantly delaying the material fracture process (thus improving plasticity) by continuously transferring the load and passivating the crack [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. During final necking stage, cracks propagate into γ phase interior, ultimately leading to failure. In contrast, BM alloy has a lower γ phase volume fraction, which makes it difficult to transfer loads and bridge cracks(Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee). At the same time, cracks tend to propagate along the W-W grain boundaries or W/γ phase boundaries, which are not conducive to improving plasticity.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"4 Conclusions","content":"\u003cp\u003eIn summary, our work reports a novel freeze-drying and liquid phase sintering technique to optimize microstructure of W-Ni-Fe alloy. Results show that the ultrafine size of nanopowder helps to restrain Ostwald ripening and achieve W grain refinement. And the high surface of nanopowder can better drive capillary penetration and realize the homogenization of high γ phase volume. Therefore, the W-Ni-Fe alloy simultaneously combines ultrafine W grains (28.3 \u0026micro;m), low W-W connectivity (Cw-w\u0026thinsp;=\u0026thinsp;0.31) and suitable γ phase volume fraction (20.2%), thus overcoming the difficulty that traditional W-Ni-Fe alloys cannot simultaneously achieve the above factors. These factors lead to a perfect match between the strength (1010 MPa) and plasticity (31%), which will shed light on the further development for two phase alloy systems similar to W-Ni-Fe alloy.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e\u003cp\u003eThis work is supported by Key Laboratory of Advanced Structural Materials (Changchun University of Technology), Ministry of Education, China (Grant No. ASM-202404). This work is supported by National Natural Science Foundation of China (Grant No. 52122409), The Open Research Fund of Suzhou Laboratory (Grant No. SZLAB-1108-2024-ZD003), Beijing Natural Science Foundation (Grant No. L241037), Tianjin Natural Science Foundation (Grant No. 24JCZDJC01160) and Science and Technology Program of Tianjin (Grant No.23ZGSSSS00050).\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eChongji Wu: Investigation, Methodology, Formal analysis, Validation, Writing - Original Draft.Lu Yang: Conceptualization, Validation.Zhu Qian: Formal analysis, Methodology.Zupeng Yan: Formal analysis.Xia Sun: Supervision.Weiqiang Hu: Conceptualization, Methodology, Supervision.Zongqing Ma: Conceptualization, Validation, Supervision.All authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eData availability\u003c/h2\u003e\u003cp\u003eThe data used to support the findings of this study are available from the corresponding author upon request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eX. 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Res. 15-17 (2006) 575-580.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"advanced-composites-and-hybrid-materials","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"achm","sideBox":"Learn more about [Advanced Composites and Hybrid Materials](https://link.springer.com/journal/42114)","snPcode":"42114","submissionUrl":"https://submission.nature.com/new-submission/42114/3","title":"Advanced Composites and Hybrid Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Tungsten heavy alloys, Freeze-drying, Liquid phase sintering, Ultrafine grains, Low W-W connectivity","lastPublishedDoi":"10.21203/rs.3.rs-7043710/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7043710/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe conventional sintered W-Ni-Fe alloy encounters challenges in achieving both high strength and plasticity simultaneously, primarily due to its inadequate organizational compatibility. To address this issue, we developed a novel approach combining in-situ freeze-drying and straightforward liquid-phase sintering techniques to effectively control the microstructure of 93W-4.9Ni-2.1Fe alloys. The corresponding W-Ni-Fe alloy in this work simultaneously takes into account ultrafine W-grains (28.3 \u0026micro;m), low W-W connectivity (Cw-w\u0026thinsp;=\u0026thinsp;0.31) and suitable γ phase volume fraction (20.2%), which is currently difficult for traditional W-Ni-Fe alloys to achieve. The minute dimensions of nanopowder play a crucial role in inhibiting Ostwald ripening and facilitating W grain refinement. Additionally, the extensive surface area of nanopowder enhances capillary penetration, leading to effective homogenization of high γ phase volume. As a result, the freeze-dried W-Ni-Fe alloy simultaneously achieves high strength (1010 MPa) and high plasticity (31%), which provides a new insight for the further development of W-Ni-Fe alloy industries.\u003c/p\u003e","manuscriptTitle":"A strategy for optimizing microstructure to simultaneously improve the strength and plasticity of W-Ni-Fe alloy","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-16 08:15:11","doi":"10.21203/rs.3.rs-7043710/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-08-10T07:27:03+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-08T08:28:38+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-01T10:59:52+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"293816093246346817074632307669350954795","date":"2025-07-30T14:22:46+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"81839315900821596183159030286532211912","date":"2025-07-23T06:17:29+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"97552585351740932648866553333448295105","date":"2025-07-21T13:01:11+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-20T14:25:28+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"35719997633219804546876184817899876620","date":"2025-07-15T01:59:58+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"170070414892282511150538300339691015126","date":"2025-07-14T06:09:23+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-14T06:01:55+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-12T19:04:15+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-07-06T22:29:59+00:00","index":"","fulltext":""},{"type":"submitted","content":"Advanced Composites and Hybrid Materials","date":"2025-07-04T06:37:53+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"advanced-composites-and-hybrid-materials","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"achm","sideBox":"Learn more about [Advanced Composites and Hybrid Materials](https://link.springer.com/journal/42114)","snPcode":"42114","submissionUrl":"https://submission.nature.com/new-submission/42114/3","title":"Advanced Composites and Hybrid Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"f58a02d7-fb3d-471d-9a17-fd09ef2ab665","owner":[],"postedDate":"July 16th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-10-20T16:07:22+00:00","versionOfRecord":{"articleIdentity":"rs-7043710","link":"https://doi.org/10.1007/s42114-025-01475-y","journal":{"identity":"advanced-composites-and-hybrid-materials","isVorOnly":false,"title":"Advanced Composites and Hybrid Materials"},"publishedOn":"2025-10-16 15:58:13","publishedOnDateReadable":"October 16th, 2025"},"versionCreatedAt":"2025-07-16 08:15:11","video":"","vorDoi":"10.1007/s42114-025-01475-y","vorDoiUrl":"https://doi.org/10.1007/s42114-025-01475-y","workflowStages":[]},"version":"v1","identity":"rs-7043710","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7043710","identity":"rs-7043710","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}