Effect of surface nanocrystallization pretreatment on the microstructure and fretting wear of Ti-6Al-4V titanium alloy plasma nitrided layer

Abstract

Titanium alloys are widely used in aerospace and biomedical fields due to their excellent strength-to-weight ratio, yet their poor surface wear resistance remains a critical limitation. While plasma nitriding (PN) has proven effective in enhancing surface hardness of Ti-6Al-4V, conventional PN-treated specimens still exhibit insufficient nitride layer thickness and inadequate hardness gradients under severe fretting conditions. The potential of surface nanocrystallization (SNC) as an innovative pretreatment to synergistically enhance nitriding efficiency and wear resistance has not been systematically investigated. This paper employs shot peening (SP) technology to achieve SNC on Ti-6Al-4V titanium alloy and examines its impact on the microstructural characteristics and fretting wear performance of plasma nitrided layers. The results show that, compared to PN samples without SNC treatment, SNC-pretreated PN samples exhibit a 27 % increase in nitrided layer thickness, reaching 4.123 μm, a 26 % enhancement in nano-hardness, reaching 13.02 GPa, and smaller TiN nanograin sizes. SNC-treated PN samples penetrate the nitrided layer at a 50 N load, whereas untreated PN samples reach the substrate at a 30 N load. Additionally, SNC-treated PN samples demonstrate lower wear scar depth and wear rates across all loads. The enhanced wear resistance of the nitrided layer with SNC is primarily due to the increased thickness of the nitrided layer and the hardness enhancement from the reduced TiN grain size.