Elevated-temperature wear behavior of Ti6Al4V alloy: microstructural evolution and properties change in subsurfaces and mild-severe wear transition

Dry sliding wear behavior of Ti6Al4V alloy was studied at elevated temperatures of 50 degrees C-400 degrees C. The constituent phases and morphologies of worn surfaces were examined to evaluate the roles of oxide layers and wear mechanisms in mild-severe wear transition (M-SWT). Microstructural evolution and hardness change in subsurfaces were also investigated to reveal the most fundamental reason for M-SWT. The results showed that M-SWT happened via severe plastic deformation (SPD) within 20 degrees C-350 degrees C, while mild wear prevailed via a protective mechanically mixed layer (MML) containing multiple oxide phases at 400 degrees C. Large surface plastic deformation and frictional heat activated dynamic recrystallization (DRX) softening in subsurface, which resulted in M-SWT. The critical load for M-SWT presented an approximate linear relationship with testing temperature within 20 degrees C-250 degrees C, from which a critical temperature of 555.8 degrees C for M-SWT was obtained by linearly fitting method. It was thought as the critical temperature for DRX realization in surface layer, and it was utilized to calculate the transition loads at 300 degrees C and 350 degrees C.