Study On The Structure And Properties Of Surface Self-Nanometerlayer In TLM Titanium Alloy

As a new type of near-beta biomedical titanium alloy,TLM alloy has the characteristics of low elastic modulus,high plastic toughness,medium and high strength,good wear resistance and high fatigue strength.However,the development of biomedicine has put forward higher requirements for further improving the biocompatibility,mechanical compatibility and mechanical processing properties of TLM titanium alloy.Therefore,the surface nanocrystallization on TLM titanium alloy was investigated by using the high-energy shot peening?HESP?in this paper.The influence of different shot peening time on its grain diameter,surface roughness and mechanical properties parameters was discussed.The thermal oxidation behavior and properties of TLM titanium alloy after high energy shot peening were studied by thermal oxidation treatment at 10h³0h.The contents and results are as follows:The surface of the TLM titanium alloy treated with different high-energy shot peening time forms a surface layer of nano-structured structure,and the grain size shows a gradually increasing gradient.Based on XRD test results,with the increase of shot peening time,the grain diameter is refined to the nanometer scale,and the degree of refinement increases with the shot peening time in a certain time range.When the shot peening time is 15min,the surface grain diameter of the sample drops sharply from the initial 20?m to 84.5nm,and the minimum value of the surface grain diameter?30.5nm?appears at the shot peening time of60min.The surface roughness of TLM titanium alloy increased firstly and then gradually decreased to a gradual stable trend.The maximum Ra value was 3.679?m?shot peening time15min?,and the three-dimensional surface morphology was smooth from flat to undulating and gradually stable;After high-energy shot peening,the microhardness increased from234HV_0.03 of the substrate to 375HV_0.03?shot peening time 60min?,an increase of 60%.Based on the microindentation technique,the mechanical properties of TLM titanium alloy before and after HESP treatment and the relationship between stress and strain curves in plastic phase were obtained.The elastic modulus before HESP treatment is about 70.085GPa,which is close to the theoretical value of 69GPa.The hardness value is about 2.238GPa,and the stress-strain relationship of plastic phase is??28?0.339??1?10?207.478?_p?^0.356.The elastic modulus after HESP treatment decreased with the increase of shot peening time,and increased with the increase of the shot peening surface.The minimum elastic modulus appeared at the top surface position of 60min,which was about 59.026GPa,a decrease of15.78%.The strain hardening index and the yield stress minimum occur at 15min and the distance from the surface is 150?m,respectively,n=0.351,?_y=0.353GPa,slightly higher than the matrix value n=0.356,?_y=0.339GPa;On this basis,the stress-strain relationship during the plastic deformation of TLM medical titanium alloy under different shot peening time was obtained.The thermal oxidation behavior of TLM titanium alloy before and after HESP treatment was investigated.The thickness of the surface thermal oxide layer of HESP 30min sample treated at 750°C for 10h,15h,20h,25h,30h was 2.33?m,3.76?m,22.89?m,26.75?m,38.02?m.Shedding occurred at 30h,and the main component of the surface thermal oxide layer was rutile TiO₂ with good hardness and wear resistance;The hardness of the oxide layer increased significantly and increased with the oxidation time.It tends to be stable at 25h,and the thermal oxidation treatment has less influence on the surface roughness.The stress-strain relationship during the plastic deformation of TLM titanium alloy under different oxidation time was obtained by the mechanical properties obtained by microindentation.