Ultrasonic impact treatment of Ti-based amorphous alloy: Improved tribological performance in air and 3.5 % NaCl solution

The inherent brittleness of amorphous alloys limits their tribological properties. Ultrasonic impact treatment (UIT), applied without preloading, has been used to improve the tribological performance of Ti-based amorphous alloys. Following UIT, the impacted surface softened, whereas the sample cross-section hardened. The change in hardness could be controlled by varying the UIT duration and ultrasonic power. UIT leads to an increase in relaxation enthalpy, suggesting higher free volume and enhanced plasticity. This improved plasticity is evidenced by the Vickers indentation morphologies and the pop-in phenomena of the nanoindentation curves. Regardless of whether the tribology testing was performed in air or in a 3.5 % NaCl solution, UIT led to noticeable reductions in both the coefficient of friction (COF) and the wear rate. The corrosion resistance improved noticeably in both static and sliding states. The primary wear mechanisms were adhesion, abrasion, and delamination. Compared to sliding in air, the COF and wear rate were lower in the NaCl solution. Post UIT, the higher free volume facilitates oxidation in air and the formation of protective corrosion products in the NaCl solution, which is beneficial in reducing adhesion. Simultaneously, the improved plasticity of UIT may contribute to resistance to fatigue and delamination. Therefore, UIT is a simple and feasible method for significantly improving the tribological performance of amorphous alloys.