Abstract: Tantalum (Ta), despite its exceptional corrosion resistance and thermal stability, suffers from poor wear performance that limits its use in friction-intensive applications. In this study, microwave plasma carburization (MPC) was employed as an advanced surface engineering strategy to address this challenge by enabling temperature-controlled tailoring of phase composition and microstructure in Ta-C layers. By adjusting the carburization temperature from 850 to 1000 °C, a deliberate evolution from a mixed Ta₂C-TaC structure to a dense, nanocrystalline TaC-rich layer with a well-developed compositional gradient was achieved. The engineered microstructure exhibits small-angle grain boundaries within the TaC layer and dislocation networks at the TaC/Ta₂C interface, collectively acting as interface-induced strengthening mechanisms. These structural features facilitate stress accommodation while suppressing surface defects. At 950 °C, the optimized layer reaches a hardness of 27.02 GPa and an elastic modulus of 520.8 GPa—significantly surpassing untreated Ta. Tribological assessments under dual-counterface conditions (GCr15 and Si₃N₄) confirm a three orders-of-magnitude reduction in wear rate (2.81 × 10^-7 mm³/(N m)) and a stable friction coefficient (∼0.30), demonstrating consistent performance across both metallic and ceramic contacts. Overall, this work establishes MPC as a rapid, controllable, and effective approach for generating gradient Ta-C layers with enhanced mechanical integrity and wear resistance. The findings offer new insights into phase-structure-property relationships and provide a robust foundation for designing durable surface systems in demanding operational environments.

Key words: Ta-C carburized layer, Microwave plasma carburization, Microstructural evolution, Gradient structure, Mechanical performance, Tribological performance