Grain boundary–dominated nitrogen diffusion during plasma nitriding of deformed TA2 alloy

Low-temperature plasma nitriding of titanium alloys is limited by sluggish nitrogen diffusion and interfacial property mismatch. Here, cold deformation pretreatment was employed to regulate the nitriding behavior of TA2 titanium alloy. The nitrided layer consists of TiN, ε-Ti₂N and α-Ti(N), while deformation significantly modifies the nitrogen gradient and microstructural evolution without altering phase constitution. EBSD analysis demonstrates that recrystallized grain refinement and increased grain boundary density dominates nitrogen diffusion during nitriding. In contrast, dislocations induced by deformation play a negligible role in nitrogen diffusion and disappear after a relatively short period. An optimal deformation degree of 30% produces the smoothest hardness gradient. Consequently, despite a reduced surface hardness, the 30% deformed sample exhibits the lowest wear rate. These findings reveal a grain boundary–controlled mechanism in deformation-assisted plasma nitriding and provide insight into the design of efficient low-temperature nitriding strategies for α-type titanium alloys.