Laser Directed Energy Deposition of Stellite 21-WC/Co coatings: processability, microstructure and dry-sliding wear behavior

Laser Directed Energy Deposition (L-DED) is an effective technique for repairing and surface-engineering of components subjected to severe wear, enabling localized control of surface properties and extended service life. In this study, Stellite 21–based metal matrix composite (MMC) coatings reinforced with WC/Co 88/12 were deposited by L-DED on AISI 316 L steel, systematically varying the WC/Co content up to 30 wt% to investigate process–microstructure–property relationships. Deposition parameters were tailored for each Stellite 21 + WC/Co composition to ensure coating integrity. Crack-free coatings with relative densities above 99% were achieved for reinforcement contents up to 20 wt% WC/Co, identifying this range as optimal. The coatings exhibit a refined CoCr-based dendritic/cellular matrix with an increasing fraction of eutectic constituents containing ultrafine carbides as WC/Co content increases, rather than WC agglomerates. This microstructure leads to a significant improvement in mechanical properties, with hardness values exceeding 800 HV1 for the 20 wt% WC/Co coating. Tribological behavior was evaluated under dry sliding conditions against AISI 52100 in a block-on-ring configuration for coatings containing up to 20 wt% WC/Co. Results show a systematic reduction in both friction coefficient and wear depth with increasing WC/Co content. Notably, the Stellite 21 + 20 wt% WC/Co coating exhibits an approximately 90% reduction in wear depth compared to unreinforced Stellite 21. These results highlight the correlation between WC/Co-induced microstructural refinement and enhanced tribological performance, demonstrating the potential of L-DED-processed Stellite 21-based MMC coatings for advanced wear-resistant applications.