Structure and tribological evolution of Ta-N layer by controlling the time of microwave plasma nitriding

To enhance the mechanical properties and wear resistance of the Ta matrix, a Ta-N layer was synthesized on its surface via microwave plasma nitriding (MPN). A systematic investigation was carried out to study the influence of holding time on the phase composition, morphology, mechanical properties, friction behavior, and wear characteristics of the nitriding layers. The results demonstrated that nanocrystalline Ta-N layers with a dense surface and low roughness were successfully fabricated. As the holding time was extended, the thickness of the Ta-N layer increased from 0.87 to 4.23 μm. Specifically, the Ta-N layer formed at 4 h, featuring a nanocrystalline structure, a dense surface, and appropriate thickness, displayed excellent mechanical properties. It had a hardness value of 26.89 GPa, an H/E ratio of 0.109, an H3/E2 value of 0.318 GPa, and an ηw value of 0.634, all of which were significantly higher compared to those of pure Ta. The friction and wear test results indicated that the Ta-N layer showed the best wear resistance when the holding time was 4 h. This was mainly ascribed to the synergy between the dense structure and the formation of nanocrystals. In summary, through MPN treatment, a Ta-N layer with the desired hardness and wear resistance was achieved, providing excellent surface protection for the Ta matrix against wear.