Microstructure Evolution And Wear Properties Of Biomedical Tatinuim Alloy Processed By Friction Stir Processing(FSP)

Ti-35Nb-3Zr-2Ta(wt%) β type titanium alloys are extensively used in medical fields due to their low elastic modulus, good biocapatibility, non-toxic elements. However, compare to other biological implants, such as Ti-6Al-4V, its strength and wear resistance need to be improved. Therefore, it is necessary to explore a way to improve the surface properties of Ti-35Nb-3Zr-2Ta(wt%) alloy. Friction Stir Processing(FSP) as one of the severe plastic deformation(SPD) method, which can arouse intense material flow and lead to effective grain refinement thus can obtain high-performance surface.In this paper, the Ti-35Nb-3Zr-2Ta(wt%) β biomedical titanium alloy and pure titanium alloy was processed by friction stir processing. The effect of FSP processing parameters( including rotating speed and processing passes) on the microstructure and wear properties of Ti-35Nb-3Zr-2Ta and pure titanium alloy were investigated.The results showed, stir zone have gone through severe plastic deformation, resulted in a uniform recrystallized structure, nanocrystalline structure was obtained under 375r/min, 3 pass. Stress-induced α″ martensite(SIM) was observed under all processing parameters, and the volume of α″ martensite increased with the processing parameters improved from one pass to three pass. ω phase was observed under one pass and two pass processing condition. The dominant deformation mechanisms changed from stress-induced α″ martensitic transformation to twinning and nanostructuring with FSP passes increasing. A reverse deformation-induced ω to β transformation and de-twinning process was observed along with the refined grains to nanoscale.The distribution of microhardness shows that the microhardness of stir zone(SZ) is much higher than that of base material(BM), the highest microhardness of stir zone was 246.7Hv, improved 30.3% compare to base material.The wear rate and average coefficient of friction of Ti-35Nb-3Zr-2Ta alloy decreased with the improving of processing passes. Wear mechanism was mainly dominated by adhesive wear under low degree of deformation and delamination tear was observed. When the amount of deformation increases, the wear mechanism changed to abrasive wear, and spalling plow was observed.