Effect of supersonic fine particle bombardment on microstructure and fatigue properties of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy at different temperatures

In this work, supersonic fine particle bombardment (SFPB) was applied to modify surface of TC11 alloy and its impacts on microstructure and fatigue properties were systematically studied. The modified surface owned a nanoscale grain structure and a compressive residual stress with an amplitude of -196 MPa. The depth of hardened layer was about 300 um. Afterwards, high-cycle fatigue behavior of SFPB modified alloy at -30 degrees C, 25 degrees C and 150 degrees C was studied, and the fracture surface, microstructure evolution, residual stress relaxation and microhardness of Ti alloy were characterized. The results show that the fatigue strength of the alloy is significantly improved by SFPB, and the fatigue strength decreases with the testing temperature. The deformation-induced martensite appears in the subsurface structure of Ti alloy tested at 25 degrees C and 150 degrees C, and the amount of deformation-induced martensite increases with the fatigue loading temperature. The compressive residual stress field induced by SFPB is relaxed in different degrees during fatigue loading. The degree of residual stress relaxation is the lowest under fatigue loading at 150 degrees C due to low cycle life. Mechanisms leading to the microstructural evolution and mechanical property variations were also proposed.