Wear- and Surface-Fatigue-Mediated Damage during Fretting in a High-Strength Titanium Alloy

Fretting damage is a key factor restricting the reliability and long life of high-strength titanium alloy fasteners. The fretting damage mechanisms correlated by the interplay relationship between wear damage and surface fatigue damage still need to be addressed. In the present work, fretting damage mechanisms of a high-strength titanium alloy (Ti-15Mo-2.7Nb-3Al-0.25Si, in wt %) were studied in depth. To represent the different matches of strength and toughness, three microstructures with different volume fractions of the primary alpha phase (A-20%, B-10%, C-1%) were applied to fretting wear tests. The evolution process of fretting wear effected by different microstructures is simulated and quantitatively combined with the sectional inclined angle of scars and the antiwear velocity of wear debris. The results demonstrate that the final worn volume of B-10% is the greatest and the best fretting wear resistance is achieved in A-20%. For wear damage, due to both the poor protective effect of the tribolayer and the fact that the tribolayer is hard to compact, B-10% has the highest wear velocity. For surface fatigue damage, the slip ratio was calculated and used as a bridge to correlate and predict wear damage and fatigue damage. The microcrack damage is most severe in C-1% but slight in A-20%. This study provides valuable experimental data for the prediction of fatigue life for fretting of titanium fasteners, and the quantitative analysis method could be generalized to other alloys.