Influence of nitriding time on the microstructural evolution, mechanical properties, and tribological performance of Ti–N nitrided layers via microwave plasma nitriding

Microwave plasma nitriding is an effective technique for enhancing the surface properties of titanium, particularly its hardness and wear resistance. This study systematically investigates the influence of nitriding time (1–5 h) on the phase transformation, microstructure, mechanical properties, and tribological behavior of the nitrided layers. The results reveal a phase transition from α-Ti to a dual-phase composition of TiN and Ti2N with increasing nitriding time, accompanied by a shift in the preferred orientation of TiN from the (111) plane to the (200) plane. Surface morphology transitioned from smooth and dense at short durations to rough and porous with extended treatment. Furthermore, the nitrogen concentration gradient across the nitrided layer became progressively more uniform as nitriding time increased. Mechanical testing showed significant improvements in hardness and elastic modulus, peaking at 30.52 and 333.53 GPa, respectively, after 5 h of nitriding. Tribological analysis indicated that a nitriding duration of 3 h achieved the optimal balance of low friction and wear resistance, attributed to the formation of a compact and well-adhered nitrided layer with favorable surface characteristics.