Microstructure and corrosion resistance of c-BN/NiCrAl coatings synthesized by laser cladding

Cubic boron nitride (c-BN) microparticles reinforced Ni-Cr-Al coatings were prepared on the surfaces of Q345R steel substrates using the laser cladding method. The c-BN particles were retained in the coating through mechanical alloying and subsequent laser treatment at low heat inputs. The effects of laser scanning speed on the microstructure, chemical composition, microhardness and corrosion resistance of the coating were investigated. The results showed that the surface roughness, thickness and uniformity of the coating were improved with the increase in laser scanning speed. The coatings were alloyed and new phases such as AlNi, AlCr₂B₂, Cr₅B₃, Al₂O₃ and h-BN formed during the laser treatment. At a laser scanning speed of 100 mm/s, the composite structure of the coating became more uniform and dense. The coating exhibited the lowest corrosion potential and corrosion current density, as well as the highest charge transfer resistance and microhardness compared to coatings synthesized at other parameters. The enhanced corrosion resistance was attributed to the formation of dense passivation films, which were associated with the more uniformly distributed c-BN reinforcement particles. The highest microhardness value of the coating reached approximately 900 HV_0.05. In general, the as-synthesized coating had the potential to improve the surface corrosion resistance and significantly enhance the surface microhardness of the steel substrates.