A study on microstructure and flame erosion mechanism of a graded Ni–Cr–B–Si coating prepared by laser cladding

The graded coating of Ni–Cr–B–Si alloy was prepared on a low carbon steel substrate by a laser cladding process. Its microstructure, hardness and flame erosion mechanisms were measured and analyzed. The flame erosion tests at 1300 °C were carried out with variable angle, velocity and time duration of particle impacting. It is found that the coating consists mainly of γ-Ni solid solution, FeNi3/Ni33Si12 eutectic and CrB ceramic phase, and has a graded hardness variation with an average value of about seven times that of the substrate material. The main flame erosion mechanism of the coating changed from brittle to ductile deformation depending on impact time, angle and velocity, and manifested by lamellar stratifying, oxide particle splashing, incising, grooving and extrusion. The impact angle is found to play a key role in the mass loss of the coating under flame erosion.