Dry Sliding Wear Behavior of a Selected Titanium Alloy Against Counterface Steel of Different Hardness Levels

Dry sliding wear tests of a selected titanium alloy (Ti-6.5Al-3.5Mo-1.5Zr-0.3Si) against AISI 52100 steel of three hardness levels were carried out at room temperature over a sliding speed range of 1 to 4 m/s. The influence of counterface hardness and sliding speed on the wear behavior and wear regime of the titanium alloy was investigated. The results show that the wear rate of the titanium alloy at 1 m/s was inversely proportional to the counterface hardness and roughly proportional to it at higher speeds. Regardless of the counterface hardness, severe and mild wear prevailed at 1 to 2 and 4 m/s [except under 50 N (2.548 MPa)], respectively. At 3 and 4 m/s-50 N (2.548 MPa), a mild-to-severe wear transition emerged with an increase in the hardness differential between the disc and pin. The wear of the titanium alloy was considered to be strongly governed by the nature of the tribo-layer. A metallic-dominated tribo-layer containing little or no oxide was responsible for severe wear at 1 to 2 m/s. However, at 4 m/s, more tribo-oxides (notably Fe₂O₃ with a high sinterability transferred from softer counterfaces) promoted the formation and solidification of ceramic tribo-oxide layers, resulting in mild wear. For harder counterfaces, due to the limited amount of transferred Fe₂O₃, the stability of tribo-oxide layers was readily destroyed, and thus, the mild-to-severe wear transition occurred at 3 and 4 m/s under 50 N (2.548 MPa).