Effect of severe plastic deformation on the structure, microhardness, and wear resistance of the surface layer of titanium subjected to gas nitriding

The effect of severe plastic deformation under dry sliding friction on the structure, microhardness, and wear rate of the VT1-0 titanium subjected to gas nitriding has been studied. It has been shown that this deformation leads to the formation of a nanocrystalline structure with an α-crystal size of 10–100 nm and a microhardness of ∼3.1 GPa in a surface layer up to 10 μm thick. The presence of this structure intensifies the saturation of the surface of the titanium with nitrogen in the course of subsequent gas nitriding at temperatures of 650–750°C. The formation of the nitride nanocrystalline TiN phase in the deformed titanium occurs at a relatively low nitriding temperature (700°C) and a short-term holding (2 h). The volume fraction of the nitride phase, which is formed in the layer up to 10 μm thick, reaches a few tens of percent, which leads to an increase in the microhardness of the nitrided surface of the titanium deformed by friction. Preliminary severe plastic deformation has a negative effect on the fatigue wear resistance of the nitrided titanium due to an increased brittleness of the deformed and subsequently nitrided surface layer of this material.