Influence of Mo contents on optimizing the microstructure and tribological properties of Cr-Mo-N films

Influence of Mo contents on optimizing the microstructure and tribological properties of Cr-Mo-N films | 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 Influence of Mo contents on optimizing the microstructure and tribological properties of Cr-Mo-N films Fanlin Kong, Jing Luan, Hongbo Ju This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4324033/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 The Cr-Mo-N films of different Mo contents are developed by the RF (Radio Frequency) magnetron sputtering. The XRD (X-ray Diffraction), SEM (Scanning Electron Microscope), EDS (Energy Dispersive Spectroscopy), nano-indenter and tribo-tester will be used to analyze the composition, phase structure, mechanical and tribological properties of films. The results reveal that the Cr-Mo-N film adopts a face-centered cubic structure, primarily oriented along the (111) plane. When the Mo content falls below 17.72%, increasing the Mo concentration leads to a slight increase in film microhardness, accompanied by a significant decrease in the average friction coefficient. On the contrary, exceeding a Mo content of 22.76% triggers structural changes within the film. These alterations are reinforced by solid solution and fine grain strengthening, further compounded by the presence of Mo 2 N. Consequently, film microhardness undergoes a considerable increase, while the average friction coefficient remains relatively stable irrespective of Mo content. This underscores the consistent low friction coefficient characteristic exhibited by Mo 2 N films. RF magnetron sputtering. Cr-Mo-N films phase structure tribological properties Figures Figure 1 Figure 2 Figure 3 1. Introduction With the high-speed development of modern manufacturing industry, there is an urgent need to elevate the materials employed in cutting tools. To meet the escalating demands of the industry, these materials must embody optimized characteristics, including superior mechanical resilience, thermal endurance, and tribological efficiency. Consequently, the quest for innovative materials tailored for cutting tools presents a formidable undertaking for scientists and engineers alike [ 1 – 2 ]. Building upon prior research, the utilization of thin film technology emerges as a pivotal avenue for enhancing both mechanical and tribological properties. Among these thin films, transitional metal nitrides (TMN) hold particular significance due to their relatively high hardness and exceptional tribological characteristics. Among TMN films, CrN stands out as a prime example of binary films, renowned for its robust film-substrate bonding, superior corrosion resistance, and admirable thermal stability, extensive application in the cutting tools industry [ 3 – 6 ]. However, CrN films exhibit certain drawbacks, including modest hardness and a relatively elevated friction coefficient [ 7 ], constraining their broader utility in tool manufacturing. To overcome these limitations, researchers have turned to the integration of specific alloying elements into CrN coatings [ 8 ]. Add an appropriate amount of Magnéli phase-forming elements to the hard film can effectively improve the friction and wear properties of the film, allowing the film to be used continuously under extreme working conditions [ 9 ]. These elements can combine with O 2 in the environment during friction to form oxides with unique shear properties and lubrication. The Magnéli phase MoO 3 with low shear modulus formed by Mo during the friction and wear process has good wear resistance and friction reduction effects [ 10 ]. Presently, the enhancement of mechanical and tribological properties in CrN-based films primarily involves the incorporation of elements such as Al [ 11 ], Si [ 12 ], W [ 13 ], Ag [ 14 ], Cu [ 15 ], and Mo [ 16 ]. Furthermore, exploration extends to the fabrication of intricate structures like CrN/MoN multilayers and composite Cr-Mo-N configurations. Employing techniques such as sputtering or hybrid physical vapor deposition (PVD), these endeavors aim to capitalize on synergistic effects to elevate the performance characteristics of these coatings, paving the way for further advancements in cutting tool materials [ 17 – 18 ]. The Mo element has garnered growing attention from researchers worldwide in recent years. Studies have revealed that Mo possesses a unique ability to form self-lubricating oxides when subjected to friction, leading to a reduction in the average friction coefficient observed in Mo-containing films [ 19 – 20 ]. It has been documented that Ti-Mo-N films with elevated Mo content exhibit superior mechanical characteristics, alongside enhanced friction and wear resistance properties. According to our previous research [ 21 ], this phenomenon is caused by the structural transformation of Ti-Mo-N films with high Mo content. Dongli Qi et.al [ 22 ] investigated the mechanical, microstructural and tribological properties of reactive magnetron sputtered Cr-Mo-N films and found that the elastic recovery played an important role in the tribological behavior. Lu Yu-chun [ 23 ] revealed that the Cr-Mo-Si-N coatings at the elevated temperature showed superior mechanical and tribological characteristics with 7.5 at.% Si doping .This paper designs a series of Cr-Mo-N films with different Mo contents by using radio frequency magnetron sputtering. Furthermore, detailed investigations into the phase structure variations of Cr-Mo-N films with differing Mo contents are conducted, accompanied by comprehensive analyses of their mechanical and frictional properties. 2. Experimental details In this experiment, a Cr target with a diameter of 75 mm and a purity of 99.95% and a Mo target with a purity of 99.9%, JGP450 composite high vacuum multi-target magnetron sputtering equipment was used to prepare thin films of different compositions on single crystal Si. The experimental process is as follows: the base material is ultrasonically cleaned in absolute ethanol and acetone for 15 minutes, dried with hot air, and then placed on a rotatable base frame in a vacuum chamber. The distance between the fixed target and the base is fixed at 11 cm; the vacuum is evacuated. After the background vacuum degree of the vacuum chamber is better than 6.0×10 − 4 Pa, high-purity Ar with a purity of 99.999% is introduced to start an arc. The substrate is blocked with a baffle, and each target is pre-sputtering for 10 minutes to remove the oxide on the target surface. and impurities; remove the baffle, and then pass in high-purity N 2 with a purity of 99.999% as a reaction gas for deposition. Cr-Mo-N films with different Mo contents are obtained by adjusting the process parameters. In order to facilitate comparative analysis, CrN and Mo 2 N films were also prepared. Before preparing CrN and Cr-Mo-N thin films, pre-sputter a Cr transition layer of about 200 nm on the substrate. Before preparing the Mo 2 N thin film, pre-sputter a Mo transition layer of about 200 nm on the substrate to enhance the film-base bonding force. During the preparation process, the Cr transition layer is pre-sputtered. The flow ratio of Ar to N 2 is 10:5, the vacuum chamber pressure is 0.3 Pa, the sputtering time is 120 minutes, the substrate temperature is heated to 200°C, and the Cr target power is 100 W. By adjusting the power of the Mo target, CrN and CrN with a thickness of about 2 µm are obtained. Cr-Mo-N films with different Mo contents (atomic fractions). The microstructure of the film was analyzed using an XRD-6000 X-ray diffractometer (XRD, Cu Kα) with a voltage of 40 kV and a current of 35 mA. The microhardness of the film was tested using CPX + NHT2 + MST nanoindentation instrument. When measuring the film hardness, select 9 points for each sample for testing. These 9 points are distributed in a 3×3 array with a spacing of 10 µm. The indentation depth of the hardness test is 60—100 nm, ensuring the mechanical properties of the film. Performance is not affected by substrate. A JEM-6480 scanning electron microscope (SEM) and its attached INCA energy spectrometer (EDS) were used to observe the surface morphology of the film and analyze the Cr and Mo contents in the film. The UMT-2 CETR friction and wear testing machine was used to test the friction performance of the film. The friction form was ball-disc circumferential friction, the friction head was an Al 2 O 3 ball with a diameter of 9.38 mm, the load was 3 N, the relative speed was 50 r/min, and the friction radius was 4 mm, friction time is 30 minutes. 3. Results and discussion 3.1 The microstructure of Cr-Mo-N films Figure 1(a) shows the XRD spectra (a) and (111) crystal plane 2ɵ(b) of Cr-Mo-N films with different Mo contents (the atomic percentage of Mo relative to Cr+Mo, the same below). It can be seen from Figure (a) that the binary CrN and Mo 2 N films are both face-centered cubic structures with (111) preferred orientation; the Cr-Mo-N films are face-centered cubic structures with (111) preferred orientation. There is no free metal Mo or other elements in the figure and the nitride phase appears. In order to facilitate the analysis of the changes in the diffraction peak angle of the main crystal plane of the Cr-Mo-N film, Fig. 1(b) shows the changing trend of the (111) crystal plane 2ɵ of the film with the Mo content. From Fig. (b), it can be seen that the (111) crystal planes 2ɵ of binary CrN and Mo 2 N films are 38.179° and 37.579° respectively. When the Mo content is less than 17.72%, the (111) crystal plane 2ɵ of the Cr-Mo-N film is close to CrN; when the Mo content is greater than 22.76%, the (111) crystal face of the film is close to Mo 2 N. The calculated lattice constants and grain sizes of CrN, Mo 2 N and Cr-Mo-N films with different Mo contents are shown in Fig 2. From the figure, we can see that the lattice constant of CrN film is 0.408nm and the grain size is 23.395nm; the lattice constant of Mo 2 N film is 0.416nm and the grain size is 18.430nm; the lattice constant of Cr-Mo-N film with different Mo content is different between CrN film and Mo 2 N between films, and gradually increases with the increase of Mo content. When the Mo content is less than 17.72%, the lattice of the film is significantly higher than that of CrN; when the Mo content is greater than 22.76%, the lattice constant of the film is close to that of Mo 2 N. It can also be seen from Fig. 2 that the grain size is larger than that of CrN film and Mo 2 N film. When the Mo content is less than 17.72%, the grain size of the film gradually increases with the increase of Mo content; when the Mo content is greater than 22.76%, the grain size of the film gradually decreases with the increase of Mo content. 3.2. The mechanical and tribological properties of Cr-Mo-N films Fig. 3 shows the microhardness of CrN, Mo2N and Cr-Mo-N films with different Mo contents. It can be seen from the figure that the microhardness of binary CrN and Mo 2 N films are 14.73GPa and 25.36GPa respectively. When the Mo content is less than 17.72%, the microhardness of the Cr-Mo-N film increases slightly with the increase of Mo content; when the Mo content is greater than 22.76%, the microhardness of the Cr-Mo-N film increases significantly with the increase of Mo content. When the content is 76.13%, the film hardness reaches the highest value, with the highest value being 26.39GPa. The increase in hardness may be attributed to solid solution strengthening [24] and grain refinement [25]. On the one hand, Mo is solidly dissolved in the CrN lattice, causing lattice distortion and solid solution strengthening, which increases the hardness. However, when the Mo content is greater than 45.4%, the hardness decreases due to the emergence of mixed phases [26]. On the other hand, the reduction in grain size increases the grain boundary area, effectively preventing dislocations and intergranular slippage, thereby increasing the hardness. The average friction coefficient of CrN, Mo 2 N and Cr-Mo-N films with different Mo contents is calculated by taking the stable phase value of the friction curve with Al 2 O 3 as the friction pair, as shown in Fig. 3. From the figure, the average friction coefficients of CrN and Mo 2 N films are 0.5836 and 0.3998 respectively, and the average friction coefficient of Cr-Mo-N films is in between. When the Mo content is less than 17.72%, the flat friction coefficient of the film decreases significantly with the increase of the Mo content. Therefore, the introduction of Mo element can significantly reduce the average friction coefficient of the CrN film, which is consistent with the research conclusion of the literature [27]; when the Mo content is greater than at 22.76%, the average friction coefficient of the film is small and is not greatly affected by the Mo content. 3.3 Discussion Since the diffraction peak positions of the main crystal planes of binary CrN and Mo2N films prepared under the same experimental conditions are very close, it is difficult to accurately analyze the structure of Cr-Mo-N films through only a single XRD pattern. Combining Fig. 1 and 2, when the Mo content is less than 17.72%, the diffraction peak of the film is close to that of CrN, and the lattice constant increases as the Mo content increases. At this time, the film is mainly a replacement solid solution of Mo solid solution in CrN. Since the atomic radius of Mo is larger than that of Cr, the solid solution of Mo causes the lattice distortion of the film and the lattice constant becomes larger. Compared with the CrN film, the diffraction peak shifts to the small angle direction; when the Mo content is greater than 22.76%, the diffraction peak and lattice constant of the film are close to those of Mo 2 N. In addition, within this range, the grain size of the film is abnormally lower than that of the former. The hardness and average friction coefficient are both close to the binary Mo 2 N film, so the main component of the film at this time is most likely a replacement solid solution of Cr solid solution in Mo 2 N. Due to the different atomic radii of Mo and Cr, lattice distortion is caused. The lattice distortion increases the resistance to dislocation movement, making slip difficult. Slip deformation therefore becomes more difficult, thereby increasing the hardness of the film. In addition, in the replacement solid solution, due to the "pinning effect" of the Cottrell air group on the dislocations, the dislocations are firmly fixed, and the resistance to dislocation movement increases, which strengthens the film and increases the hardness of the film [28]. Kwang Ho Kim et al. [29] prepared a Cr-Mo-N film under conditions similar to the conditions of this experiment and performed XPS analysis on it. It shows that when the Mo content is greater than 21%, the peak position of the film is close to that of Mo 2 N. This experimental phenomenon supports the above analysis. Since both solid solutions have fcc structures and their diffraction angles and lattice constants are very close, they can be collectively called Cr-Mo-N solid solutions. When the Mo content is less than 17.72%, the average friction coefficient of the film decreases significantly with the increase of Mo content [30]. This shows that Mo can effectively reduce the average friction coefficient of the CrN film. When the Mo content is greater than 22.76%, the average friction coefficient of the film is small and is not greatly affected by the Mo content. Since the film is a solid solution of Cr dissolved in Mo 2 N, the film at this time reflects the low average friction coefficient of the Mo 2 N film. Studies have shown that MoO 3 with low shear modulus and self-lubricating effect is generated on the wear scar surface during the friction process [31], resulting in the low friction coefficient of the Cr-Mo-N film. Layered MoO 3 is the well-known self-lubricant tribo-phase to enhance the friction performance [32]. 4. Conclusion The Cr-Mo-N films were prepared by RF magnetron sputtering technique. The following conclusions are as follows: (1) The Cr-Mo-N film has a face-centered cubic structure with (111) preferred orientation. When the Mo content is less than 17.72%, the film is mainly a replacement solid solution of Mo solid solution in CrN. As the Mo content increases, the lattice constant and grain size of the film increase gradually. (2) the microhardness increases slightly, and the average friction coefficient significantly reduced with the increase of Mo content in the films; when the Mo content is greater than 22.76%, the film is mainly a replacement solid solution of Cr solid solution in Mo 2 N. As the Mo content increases, the lattice constant of the film gradually increases and the grain size gradually decreases. Due to the joint effects of film structural transformation, solid solution strengthening and fine grain strengthening, the microhardness of the film increases significantly compared with the previous one. (3) The average friction coefficient is not significantly affected by the Mo content, reflecting the low average friction coefficient of the Mo 2 N film. When the Mo content is less than 17.72%, the average friction coefficient of the film decreases significantly with the increase of Mo content. When the Mo content is greater than 22.76%, the average friction coefficient of the film is small and is not greatly affected by the Mo content. Statements & Declarations 1. Funding This work was supported by the National Natural Science Foundation of China with the number of 52171071 and 51801081, national funds through FCT of Portugal – Fundação para a Ciência e a Tecnologia, under a scientific contract of 2021.04115.CEECIND, 2023.06224.CEECIND, and the projects of UIDB/00285/2020, and LA/0112/2020. 2. Competing Interests The authors have no relevant financial or non-financial interests to disclose. 3. Author Contributions Fanlin Kong: Formal analysis, Data Curation, Visualization and Writing-Original Draft. Jing Luan: Data Curation, Formal analysis and Writing-Original Draft. Hongbo Ju: Conceptualization, Methodology, Validation, Supervision, Writing - Review & Editing, Supervision and Funding acquisition. References E. Y. Choi, M. C. Kang, D. H. Kwon, D. W. Shin, K. H. Kim. Comparative studies on microstructure and mechanical properties of CrN, Cr-C-N and Cr-Mo-N coatings. Journal of Materials Processing Technology. 187-188(2007): 566-570. A. V. 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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-4324033","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":296783118,"identity":"74570fdc-56ea-455d-88ee-17c54c0a7950","order_by":0,"name":"Fanlin Kong","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Fanlin","middleName":"","lastName":"Kong","suffix":""},{"id":296783119,"identity":"649f7338-38e2-4f53-a036-99f28dbf9294","order_by":1,"name":"Jing Luan","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Jing","middleName":"","lastName":"Luan","suffix":""},{"id":296783120,"identity":"96624413-a8ac-426e-8e31-7bd5438b34dc","order_by":2,"name":"Hongbo Ju","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAv0lEQVRIiWNgGAWjYBACAwmGBIYPPBCOBNFaGGcAtfCQooWBGaSceC3m0g3PpG1kDtvbMzAfvM3DYJdHUIvlnANp0jk8hxN7GNiSrXkYkosJO+xGAlhLAg8Dj5k0D8OBxAaitFjwHLbnYeD/RoIWBp7DjD0MPGxEarlzINmyhyc9secwm7HlHINkIrTc7km88bPH2p69vfnhjTcVdoS1ACMkgQHoKmDsgE0grB4I2A8wMPwgSuUoGAWjYBSMVAAAqW40kT/WRSEAAAAASUVORK5CYII=","orcid":"","institution":"Jiangsu University of Science and Technology","correspondingAuthor":true,"prefix":"","firstName":"Hongbo","middleName":"","lastName":"Ju","suffix":""}],"badges":[],"createdAt":"2024-04-25 12:08:35","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4324033/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4324033/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":56039813,"identity":"61e3222c-9e2e-4f5a-9627-ef4e6470f07e","added_by":"auto","created_at":"2024-05-07 19:13:15","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":21609,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of the Cr-Mo-N coatings with different atomic fraction of Mo\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4324033/v1/93f246f7c3a44a9376452588.png"},{"id":56039815,"identity":"82aed4bf-c3a2-4144-bc7b-5f6f29d101e6","added_by":"auto","created_at":"2024-05-07 19:13:15","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":13885,"visible":true,"origin":"","legend":"\u003cp\u003eThe lattice constant and grain size of CrN, Mo\u003csub\u003e2\u003c/sub\u003eN and Cr-Mo-N coatings for different atomic fraction of Mo\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4324033/v1/6a3dd69e79a5fbc884db5cc8.png"},{"id":56039840,"identity":"938783f5-bbca-4de6-98a5-4c75b5429f21","added_by":"auto","created_at":"2024-05-07 19:13:15","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":16264,"visible":true,"origin":"","legend":"\u003cp\u003eMicrohardness and average friction coefficient of CrN, Mo\u003csub\u003e2\u003c/sub\u003eN and Cr-Mo-N coatings with different atomic fraction of Mo\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4324033/v1/10a1ef7797254ca5cd83d283.png"},{"id":56465902,"identity":"44e600b5-f13a-4718-a46f-c96a9bffc1a3","added_by":"auto","created_at":"2024-05-14 14:39:14","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":281682,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4324033/v1/d905ebb6-ae95-4646-82bc-a63a87f4f14e.pdf"}],"financialInterests":"","formattedTitle":"Influence of Mo contents on optimizing the microstructure and tribological properties of Cr-Mo-N films","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eWith the high-speed development of modern manufacturing industry, there is an urgent need to elevate the materials employed in cutting tools. To meet the escalating demands of the industry, these materials must embody optimized characteristics, including superior mechanical resilience, thermal endurance, and tribological efficiency. Consequently, the quest for innovative materials tailored for cutting tools presents a formidable undertaking for scientists and engineers alike [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eBuilding upon prior research, the utilization of thin film technology emerges as a pivotal avenue for enhancing both mechanical and tribological properties. Among these thin films, transitional metal nitrides (TMN) hold particular significance due to their relatively high hardness and exceptional tribological characteristics. Among TMN films, CrN stands out as a prime example of binary films, renowned for its robust film-substrate bonding, superior corrosion resistance, and admirable thermal stability, extensive application in the cutting tools industry [\u003cspan additionalcitationids=\"CR4 CR5\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. However, CrN films exhibit certain drawbacks, including modest hardness and a relatively elevated friction coefficient [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], constraining their broader utility in tool manufacturing. To overcome these limitations, researchers have turned to the integration of specific alloying elements into CrN coatings [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Add an appropriate amount of Magn\u0026eacute;li phase-forming elements to the hard film can effectively improve the friction and wear properties of the film, allowing the film to be used continuously under extreme working conditions [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. These elements can combine with O\u003csub\u003e2\u003c/sub\u003e in the environment during friction to form oxides with unique shear properties and lubrication. The Magn\u0026eacute;li phase MoO\u003csub\u003e3\u003c/sub\u003e with low shear modulus formed by Mo during the friction and wear process has good wear resistance and friction reduction effects [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Presently, the enhancement of mechanical and tribological properties in CrN-based films primarily involves the incorporation of elements such as Al [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], Si [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], W [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], Ag [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], Cu [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], and Mo [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Furthermore, exploration extends to the fabrication of intricate structures like CrN/MoN multilayers and composite Cr-Mo-N configurations. Employing techniques such as sputtering or hybrid physical vapor deposition (PVD), these endeavors aim to capitalize on synergistic effects to elevate the performance characteristics of these coatings, paving the way for further advancements in cutting tool materials [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe Mo element has garnered growing attention from researchers worldwide in recent years. Studies have revealed that Mo possesses a unique ability to form self-lubricating oxides when subjected to friction, leading to a reduction in the average friction coefficient observed in Mo-containing films [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. It has been documented that Ti-Mo-N films with elevated Mo content exhibit superior mechanical characteristics, alongside enhanced friction and wear resistance properties. According to our previous research [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], this phenomenon is caused by the structural transformation of Ti-Mo-N films with high Mo content. Dongli Qi et.al [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] investigated the mechanical, microstructural and tribological properties of reactive magnetron sputtered Cr-Mo-N films and found that the elastic recovery played an important role in the tribological behavior. Lu Yu-chun [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e] revealed that the Cr-Mo-Si-N coatings at the elevated temperature showed superior mechanical and tribological characteristics with 7.5 at.% Si doping .This paper designs a series of Cr-Mo-N films with different Mo contents by using radio frequency magnetron sputtering. Furthermore, detailed investigations into the phase structure variations of Cr-Mo-N films with differing Mo contents are conducted, accompanied by comprehensive analyses of their mechanical and frictional properties.\u003c/p\u003e"},{"header":"2. Experimental details","content":"\u003cp\u003eIn this experiment, a Cr target with a diameter of 75 mm and a purity of 99.95% and a Mo target with a purity of 99.9%, JGP450 composite high vacuum multi-target magnetron sputtering equipment was used to prepare thin films of different compositions on single crystal Si. The experimental process is as follows: the base material is ultrasonically cleaned in absolute ethanol and acetone for 15 minutes, dried with hot air, and then placed on a rotatable base frame in a vacuum chamber. The distance between the fixed target and the base is fixed at 11 cm; the vacuum is evacuated. After the background vacuum degree of the vacuum chamber is better than 6.0\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e Pa, high-purity Ar with a purity of 99.999% is introduced to start an arc. The substrate is blocked with a baffle, and each target is pre-sputtering for 10 minutes to remove the oxide on the target surface. and impurities; remove the baffle, and then pass in high-purity N\u003csub\u003e2\u003c/sub\u003e with a purity of 99.999% as a reaction gas for deposition. Cr-Mo-N films with different Mo contents are obtained by adjusting the process parameters. In order to facilitate comparative analysis, CrN and Mo\u003csub\u003e2\u003c/sub\u003eN films were also prepared. Before preparing CrN and Cr-Mo-N thin films, pre-sputter a Cr transition layer of about 200 nm on the substrate. Before preparing the Mo\u003csub\u003e2\u003c/sub\u003eN thin film, pre-sputter a Mo transition layer of about 200 nm on the substrate to enhance the film-base bonding force. During the preparation process, the Cr transition layer is pre-sputtered. The flow ratio of Ar to N\u003csub\u003e2\u003c/sub\u003e is 10:5, the vacuum chamber pressure is 0.3 Pa, the sputtering time is 120 minutes, the substrate temperature is heated to 200\u0026deg;C, and the Cr target power is 100 W. By adjusting the power of the Mo target, CrN and CrN with a thickness of about 2 \u0026micro;m are obtained. Cr-Mo-N films with different Mo contents (atomic fractions).\u003c/p\u003e \u003cp\u003eThe microstructure of the film was analyzed using an XRD-6000 X-ray diffractometer (XRD, Cu Kα) with a voltage of 40 kV and a current of 35 mA. The microhardness of the film was tested using CPX\u0026thinsp;+\u0026thinsp;NHT2\u0026thinsp;+\u0026thinsp;MST nanoindentation instrument. When measuring the film hardness, select 9 points for each sample for testing. These 9 points are distributed in a 3\u0026times;3 array with a spacing of 10 \u0026micro;m. The indentation depth of the hardness test is 60\u0026mdash;100 nm, ensuring the mechanical properties of the film. Performance is not affected by substrate. A JEM-6480 scanning electron microscope (SEM) and its attached INCA energy spectrometer (EDS) were used to observe the surface morphology of the film and analyze the Cr and Mo contents in the film. The UMT-2 CETR friction and wear testing machine was used to test the friction performance of the film. The friction form was ball-disc circumferential friction, the friction head was an Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e ball with a diameter of 9.38 mm, the load was 3 N, the relative speed was 50 r/min, and the friction radius was 4 mm, friction time is 30 minutes.\u003c/p\u003e"},{"header":"3. Results and discussion","content":"\u003cp\u003e3.1\u0026nbsp;The microstructure of Cr-Mo-N films\u003c/p\u003e\n\u003cp\u003eFigure 1(a) shows the XRD spectra (a) and (111) crystal plane 2ɵ(b) of Cr-Mo-N films with different Mo contents (the atomic percentage of Mo relative to Cr+Mo, the same below). It can be seen from Figure (a) that the binary CrN and Mo\u003csub\u003e2\u003c/sub\u003eN films are both face-centered cubic structures with (111) preferred orientation; the Cr-Mo-N films are face-centered cubic structures with (111) preferred orientation. There is no free metal Mo or other elements in the figure and the nitride phase appears.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn order to facilitate the analysis of the changes in the diffraction peak angle of the main crystal plane of the Cr-Mo-N film, Fig. 1(b) shows the changing trend of the (111) crystal plane 2ɵ\u0026nbsp;of the film with the Mo content. From Fig. (b), it can be seen that the (111) crystal planes 2ɵ\u0026nbsp;of binary CrN and Mo\u003csub\u003e2\u003c/sub\u003eN films are 38.179\u0026deg; and 37.579\u0026deg; respectively. When the Mo content is less than 17.72%, the (111) crystal plane 2ɵ\u0026nbsp;of the Cr-Mo-N film is close to CrN; when the Mo content is greater than 22.76%, the (111) crystal face of the film is close to Mo\u003csub\u003e2\u003c/sub\u003eN.\u003c/p\u003e\n\u003cp\u003eThe calculated lattice constants and grain sizes of CrN, Mo\u003csub\u003e2\u003c/sub\u003eN and Cr-Mo-N films with different Mo contents are shown in Fig 2. From the figure, we can see that the lattice constant of CrN film is 0.408nm and the grain size is 23.395nm; the lattice constant of Mo\u003csub\u003e2\u003c/sub\u003eN film is 0.416nm and the grain size is 18.430nm; the lattice constant of Cr-Mo-N film with different Mo content is different between CrN film and Mo\u003csub\u003e2\u003c/sub\u003eN between films, and gradually increases with the increase of Mo content. When the Mo content is less than 17.72%, the lattice of the film is significantly higher than that of CrN; when the Mo content is greater than 22.76%, the lattice constant of the film is close to that of Mo\u003csub\u003e2\u003c/sub\u003eN.\u003c/p\u003e\n\u003cp\u003eIt can also be seen from Fig. 2 that the grain size is larger than that of CrN film and Mo\u003csub\u003e2\u003c/sub\u003eN film. When the Mo content is less than 17.72%, the grain size of the film gradually increases with the increase of Mo content; when the Mo content is greater than 22.76%, the grain size of the film gradually decreases with the increase of Mo content.\u003c/p\u003e\n\u003cp\u003e3.2. The mechanical and tribological properties of Cr-Mo-N films\u003c/p\u003e\n\u003cp\u003eFig. 3 shows the microhardness of CrN, Mo2N and Cr-Mo-N films with different Mo contents. It can be seen from the figure that the microhardness of binary CrN and Mo\u003csub\u003e2\u003c/sub\u003eN films are 14.73GPa and 25.36GPa respectively. When the Mo content is less than 17.72%, the microhardness of the Cr-Mo-N film increases slightly with the increase of Mo content; when the Mo content is greater than 22.76%, the microhardness of the Cr-Mo-N film increases significantly with the increase of Mo content. When the content is 76.13%, the film hardness reaches the highest value, with the highest value being 26.39GPa. The increase in hardness may be attributed to solid solution strengthening [24] and grain refinement [25]. On the one hand, Mo is solidly dissolved in the CrN lattice, causing lattice distortion and solid solution strengthening, which increases the hardness. However, when the Mo content is greater than 45.4%, the hardness decreases due to the emergence of mixed phases [26]. On the other hand, the reduction in grain size increases the grain boundary area, effectively preventing dislocations and intergranular slippage, thereby increasing the hardness.\u003c/p\u003e\n\u003cp\u003eThe average friction coefficient of CrN, Mo\u003csub\u003e2\u003c/sub\u003eN and Cr-Mo-N films with different Mo contents is calculated by taking the stable phase value of the friction curve with Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e as the friction pair, as shown in Fig. 3. From the figure, the average friction coefficients of CrN and Mo\u003csub\u003e2\u003c/sub\u003eN films are 0.5836 and 0.3998 respectively, and the average friction coefficient of Cr-Mo-N films is in between. When the Mo content is less than 17.72%, the flat friction coefficient of the film decreases significantly with the increase of the Mo content. Therefore, the introduction of Mo element can significantly reduce the average friction coefficient of the CrN film, which is consistent with the research conclusion of the literature [27]; when the Mo content is greater than at 22.76%, the average friction coefficient of the film is small and is not greatly affected by the Mo content.\u003c/p\u003e\n\u003cp\u003e3.3 Discussion\u003c/p\u003e\n\u003cp\u003eSince the diffraction peak positions of the main crystal planes of binary CrN and Mo2N films prepared under the same experimental conditions are very close, it is difficult to accurately analyze the structure of Cr-Mo-N films through only a single XRD pattern. Combining Fig. 1 and 2, when the Mo content is less than 17.72%, the diffraction peak of the film is close to that of CrN, and the lattice constant increases as the Mo content increases. At this time, the film is mainly a replacement solid solution of Mo solid solution in CrN.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eSince the atomic radius of Mo is larger than that of Cr, the solid solution of Mo causes the lattice distortion of the film and the lattice constant becomes larger. Compared with the CrN film, the diffraction peak shifts to the small angle direction; when the Mo content is greater than 22.76%, the diffraction peak and lattice constant of the film are close to those of Mo\u003csub\u003e2\u003c/sub\u003eN. In addition, within this range, the grain size of the film is abnormally lower than that of the former. The hardness and average friction coefficient are both close to the binary Mo\u003csub\u003e2\u003c/sub\u003eN film, so the main component of the film at this time is most likely a replacement solid solution of Cr solid solution in Mo\u003csub\u003e2\u003c/sub\u003eN. Due to the different atomic radii of Mo and Cr, lattice distortion is caused. The lattice distortion increases the resistance to dislocation movement, making slip difficult. Slip deformation therefore becomes more difficult, thereby increasing the hardness of the film. In addition, in the replacement solid solution, due to the \u0026quot;pinning effect\u0026quot; of the Cottrell air group on the dislocations, the dislocations are firmly fixed, and the resistance to dislocation movement increases, which strengthens the film and increases the hardness of the film [28]. Kwang Ho Kim et al. [29] prepared a Cr-Mo-N film under conditions similar to the conditions of this experiment and performed XPS analysis on it. It shows that when the Mo content is greater than 21%, the peak position of the film is close to that of Mo\u003csub\u003e2\u003c/sub\u003eN. This experimental phenomenon supports the above analysis. Since both solid solutions have fcc structures and their diffraction angles and lattice constants are very close, they can be collectively called Cr-Mo-N solid solutions.\u003c/p\u003e\n\u003cp\u003eWhen the Mo content is less than 17.72%, the average friction coefficient of the film decreases significantly with the increase of Mo content [30]. This shows that Mo can effectively reduce the average friction coefficient of the CrN film. When the Mo content is greater than 22.76%, the average friction coefficient of the film is small and is not greatly affected by the Mo content. Since the film is a solid solution of Cr dissolved in Mo\u003csub\u003e2\u003c/sub\u003eN, the film at this time reflects the low average friction coefficient of the Mo\u003csub\u003e2\u003c/sub\u003eN film. Studies have shown that MoO\u003csub\u003e3\u003c/sub\u003e with low shear modulus and self-lubricating effect is generated on the wear scar surface during the friction process [31], resulting in the low friction coefficient of the Cr-Mo-N film. Layered MoO\u003csub\u003e3\u003c/sub\u003e is the well-known self-lubricant tribo-phase to enhance the friction performance [32].\u003c/p\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThe Cr-Mo-N films were prepared by RF magnetron sputtering technique. The following conclusions are as follows:\u003c/p\u003e\n\u003cp\u003e(1)\u0026nbsp; \u0026nbsp;The Cr-Mo-N film has a face-centered cubic structure with (111) preferred orientation. When the Mo content is less than 17.72%, the film is mainly a replacement solid solution of Mo solid solution in CrN. As the Mo content increases, the lattice constant and grain size of the film increase gradually.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e(2)\u0026nbsp; \u0026nbsp;the microhardness increases slightly, and the average friction coefficient significantly reduced with the increase of Mo content in the films; when the Mo content is greater than 22.76%, the film is mainly a replacement solid solution of Cr solid solution in Mo\u003csub\u003e2\u003c/sub\u003eN. As the Mo content increases, the lattice constant of the film gradually increases and the grain size gradually decreases. Due to the joint effects of film structural transformation, solid solution strengthening and fine grain strengthening, the microhardness of the film increases significantly compared with the previous one.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e(3)\u0026nbsp; \u0026nbsp;The average friction coefficient is not significantly affected by the Mo content, reflecting the low average friction coefficient of the Mo\u003csub\u003e2\u003c/sub\u003eN film. When the Mo content is less than 17.72%, the average friction coefficient of the film decreases significantly with the increase of Mo content. When the Mo content is greater than 22.76%, the average friction coefficient of the film is small and is not greatly affected by the Mo content.\u003c/p\u003e"},{"header":"Statements \u0026 Declarations","content":"\u003cp\u003e\u003cstrong\u003e1. Funding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the National Natural Science Foundation of China with the number of 52171071 and 51801081, national funds through FCT of Portugal \u0026ndash; Funda\u0026ccedil;\u0026atilde;o para a Ci\u0026ecirc;ncia e a Tecnologia, under a scientific contract of 2021.04115.CEECIND, 2023.06224.CEECIND, and the projects of UIDB/00285/2020, and LA/0112/2020.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2. Competing Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3. Author Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFanlin Kong: Formal analysis, Data Curation, Visualization and Writing-Original Draft.\u003c/p\u003e\n\u003cp\u003eJing Luan: \u0026nbsp;Data Curation, Formal analysis and Writing-Original Draft.\u003c/p\u003e\n\u003cp\u003eHongbo Ju: Conceptualization, Methodology, Validation, Supervision, Writing - Review \u0026amp; Editing, Supervision and Funding acquisition.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eE. Y. Choi, M. C. Kang, D. H. Kwon, D. W. Shin, K. H. Kim. Comparative studies on microstructure and mechanical properties of CrN, Cr-C-N and Cr-Mo-N coatings. Journal of Materials Processing Technology. 187-188(2007): 566-570.\u003c/li\u003e\n \u003cli\u003eA. V. Gabrielyan, K. V. Manulyan, S. L. Kharatyan. Comparative study of combustion laws for Mo-Si-N and W-Si-N ternary systems. Journal of Alloys and Compounds. 454 (2008): 394-399.\u003c/li\u003e\n \u003cli\u003eB. Gu, J. P. 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Surface and Interfaces. 32(2022):102120.\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":"RF magnetron sputtering. Cr-Mo-N films, phase structure, tribological properties ","lastPublishedDoi":"10.21203/rs.3.rs-4324033/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4324033/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe Cr-Mo-N films of different Mo contents are developed by the RF (Radio Frequency) magnetron sputtering. The XRD (X-ray Diffraction), SEM (Scanning Electron Microscope), EDS (Energy Dispersive Spectroscopy), nano-indenter and tribo-tester will be used to analyze the composition, phase structure, mechanical and tribological properties of films. The results reveal that the Cr-Mo-N film adopts a face-centered cubic structure, primarily oriented along the (111) plane. When the Mo content falls below 17.72%, increasing the Mo concentration leads to a slight increase in film microhardness, accompanied by a significant decrease in the average friction coefficient. On the contrary, exceeding a Mo content of 22.76% triggers structural changes within the film. These alterations are reinforced by solid solution and fine grain strengthening, further compounded by the presence of Mo\u003csub\u003e2\u003c/sub\u003eN. Consequently, film microhardness undergoes a considerable increase, while the average friction coefficient remains relatively stable irrespective of Mo content. This underscores the consistent low friction coefficient characteristic exhibited by Mo\u003csub\u003e2\u003c/sub\u003eN films.\u003c/p\u003e","manuscriptTitle":"Influence of Mo contents on optimizing the microstructure and tribological properties of Cr-Mo-N films","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-05-07 19:13:10","doi":"10.21203/rs.3.rs-4324033/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":"c961b902-27fc-4fdf-8bb2-27965dfd6f8a","owner":[],"postedDate":"May 7th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-05-14T14:31:07+00:00","versionOfRecord":[],"versionCreatedAt":"2024-05-07 19:13:10","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4324033","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4324033","identity":"rs-4324033","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}