Preparation Of Molybdenum Nitride-based Thin Films And Their Tribological Properties In A Wide Temperature Range

With the further development of the economic construction in our country,the rapid development of high-tech industries,for example the aerospace industry,have brought more requirements on parts and components under harsh working conditions such as high temperature and temperature change.It is urgent to design excellent high-temperature solid lubricants materials with low friction coefficient and wear rate.Based on the synergistic mechanism of multi-lubrication phase compounding and in-situ self-generating lubrication phase on film surface,the new type of solid lubricating film with lubricating function in a wide temperature range was prepared.The influence of the multi-lubrication phase compounding on the structure and friction properties in wide temperature range of the solid lubricating films were studied,as well as the tribological mechanism of different lubricating phases under the wide temperature range was expounded.Three types of MoN-based films were deposited by magnetron sputtering technology in N₂ atmosphere,and the chemical composition,microstructure,hardness and elastic modulus of different films were characterized.The high temperature friction and wear performance of the film were tested useing a high temperature friction and wear tester.By further analyzing and characterizing the worn surface after the friction test,the tribological mechanism of the film under different temperature environments was studied.Based on the easy shear phases of MoO₃ and V₂O₅ formed by high temperature oxidation of MoN and VN,MoVN composite films were prepared.By changing the V target current and regulating the percentage content of Mo and V atom in the films,the microstructure,hardness,elastic modulus and tribological properties of different MoVN composite films were studied.The results show that the binary nitride films（MoN and VN）have poor wide temperature range friction properties,and the MoVN composite films have good friction properties in the high temperature environment.Through further explore the tribological properties of MoVN composite films,the tribological mechanism of MoVN composite films at different temperatures is clarified.By changing the rotate speed of the substrate and controlling the thickness of the MoN and VN layers in the film,MoN/VN multilayer films with different modulation periods were designed and prepared.The mechanical and tribological properties of multilayer films were explored and the effects of different modulation periods on the hardness,elastic modulus and tribological properties of MoN/VN multilayer films were compared.The results show that the hardness and elastic modulus of the film increase with the modulation period decreases,as well as the modulation period has little effect on the high temperature tribological properties of MoN/VN multilayer films.The high-temperature tribological mechanism of multilayer films is analyzed by further studying on the friction properties of MoN/VN multilayer films at different temperatures.MoVN-Ag composite films with different Ag contents were prepared based on the formation of in-situ self-lubricating films of Ag under moderate temperature.The effects of Ag-doped on the microstructure,hardness,elastic modulus and high-temperature tribological properties of the composite films were compared and studied by changing the silver target current and regulating the atomic percentage of the Ag content in the films.The results show that although the doping of Ag element weakens the hardness and bearing capacity of the films,the high-temperature lubrication performance of the films are significantly improved.Especially when the test temperature is 500^oC,the friction coefficient and wear rate of MoVN-Ag are the lowest.Through further research on the tribological properties of MoVN-Ag composite films at different temperatures,it is clarified that the diffusion of Ag and the formation of the ternary oxidation products（Ag₃MoO₄ and AgVO₃）are the main reasons for improving the high-temperature lubrication performance of Mo VN-Ag films under a wide temperature range.