Microstructure development and cavitation erosion resistance enhancement of additive manufactured Hastelloy C276 alloy coating on martensitic stainless-steel via directed energy deposition

In this study, a Hastelloy C276 coating was prepared on a martensitic stainless-steel substrate using laser melting deposition, aiming at obtaining a coating with high resistance to cavitation erosion. The coating is up to 600 mu m thick, and the grain morphology of the coating exhibits a progression from bottom to top, transitioning from cellular to columnar and ultimately to equiaxed grains. Additionally, the grains grow at a specific angle to the substrate plane, following the direction of the heat source. A 200 mu m thick compositional mixing zone is formed at the interface of the substrate and the coating, in which the coating elements and substrate elements mutually permeate and form a stable metallurgical bond. The microhardness of the coating is measured as 334.4 HV0.05, signifying a substantial improvement of 33.2 % compared to the substrate. The cavitation erosion process of the coating can be classified into three stages: incubation, accumulation, and stabilization. The material spalling damage caused by cavitation erosion progresses in a fatigued manner, and the coating demonstrates considerably enhanced resistance to cavitation erosion compared to the substrate.