In the present study, the effect of microstructure on crack growth behavior during fretting fatigue under mixed fretting regime was systematically investigated in Ti-6Al-3Nb-2Zr-1Mo (TA31) titanium alloy. Three representative microstructures, equiaxed (EM), lamellar (LM) and bimodal (BM), were obtained through controlled heat treatment routes. Fretting fatigue tests were conducted under mixed regime, followed by detailed surface, cross-sectional and crystallographic analyses to elucidate crack initiation sites and propagation paths. The results demonstrate that short cracks propagate predominantly in a transgranular manner, strongly influenced by interface characteristics. Among the three microstructures, the bimodal condition exhibits the slowest short crack growth rate and superior resistance to fretting-induced damage, whereas the lamellar microstructure shows the lowest resistance. Energy-based analysis indicates that the plastic work required for crack extension per unit length in the BM specimen is significantly higher, approximately 8.32 times that of the LM specimen. This study provides mechanistic insight into the microstructure-dependent short crack evolution under mixed fretting conditions, and offers a physical basis for improving fretting fatigue life prediction of titanium alloy components.
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Hao et al. (2026) studied this question.