Study On Mechanical Properties Of Ni-Ti Films Deposited By Sputter On Ti-6Al-4V

Due to its low density,high specific strength,good corrosion resistance and good biocompatibility,Ti-6AI-4V is widely used as biological implant material and becomes the preferred material for biological repair and artificial joint.However,due to the low hardness,high friction coefficient and poor wear resistance of Ti-6A1-4V,it is prone to wear and tear,resulting in a large amount of wear debris and the overflow of A1 and V elements,which is harmful to the organism,resulting in the failure of biological implants and seriously affecting the service life and application range of titanium alloy.Ni-Ti alloys with the same atomic number not only have good shape memory effect,corrosion resistance and biocompatibility,but also have excellent tribological properties.Therefore,it is very necessary to deposit Ni-Ti alloy film by surface modification to improve the surface hardness of Ti-6AI-4V,reduce the friction coefficient and improve the wear resistance,so as to make up for its shortcomings in application.In this project,DC magnetron sputtering is adopted.,firstly,the pretreatment process of Ti-6Al-4V is explored.By optimizing the sputtering process parameters,the Ni-Ti films with nearly equal atomic ratio were deposited,and the films were then crystallized and annealed.The effects of different process parameters on the surface morphology,roughness,grain size and phase composition of Ni-Ti films were studied.The mechanical properties of Ni-Ti films,such as adhesion strength,hardness,frictional wear,were tested,and the influences of sputtering process parameters and microstructures on mechanical properties were analyzed.Studies have shown that the pretreatment methods of substrate have significant impacts on the morphology of the film and the adhesion strength of coating-substrate.The polished substrate is processed by physical cleaning,chemical degreasing and surface acid etching activation,which can prevent the surface oxidation of the substrate,enhance the adhesion strength of coating-substrate and improve the surface quality of the film.The optimal sputtering process for Ni-Ti films was as follows:sputtering power 170W,substrate temperature 260?,bias voltage-50V,sputtering time 45min,deposition rate 97nm/min.Ni-Ti film was crystallization annealed at 600?×1h,film surface is uniform and compact,with good degree of crystallization,the average roughness is about 100nm;The atomic ratio of the film is Ni:Ti=51.05at%:48.95at%,B2 austenite at room temperature,the main crystal faces are(1 1 0)and(2 1 1).Ni-rich phases Ni4Ti3 and Ni3Ti were mainly precipitated in the film.The distribution of precipitations has great effects on the hardness of the film.The film is well combined with Ti-6Al-4V matrix,the hardness increased from 314HV0.2 to 451HV0.2,the friction coefficient drops from about 0.4 to about 0.2,the wear extent is reduced by about 80%compared with the matrix.The antifriction and wear resistance are improved obviously.