Synergistic enhancement of Re/B4C on cobalt-based composite coatings: Evolution of microstructure, microhardness and tribological properties

Abstract

In recent years, the application of laser cladded composite coatings remains a challenge due to the uneven distribution of residual stress and the formation of cracks resulting from high cooling rates and thermal gradient. Hence, we report on the elimination of cracks and softening in-situ composite coatings by doping 4.0 wt% of Rhenium(Re). The variation in transient temperature field, cladding geometry, microstructure, phase composition and tribological properties were also investigated with different laser energy input. Results indicated that B4C and Stellite-6 can significantly improve the microhardness of the TC4 substrate owing to the in-situ formation of hard phases (metallic carbides and borides), whereas accompanied with numerous cracks. More notably, the addition of Re can effectively inhibit the occurrence of cracks and soften the composite coatings, meanwhile excellent surface morphologies and wear resistance were obtained. The as-prepared composite coatings exhibit the highest microhardness with the value of 608.2HV0.2 and the minimum wear rate for 0.938 ∗ 10−7 mm2/N.