Bond strength, hardness, and microstructure analysis of stellite coating applied on 410 steel surface using flame spray, plasma spray, and high-velocity oxyfuel spray process

Three thermal spray methods often used in industry are flame spray, plasma spray, and high-velocity oxyfuel (HVOF) spray. This research is intended to compare the properties of those methods in depositing Stellite coating on 410 martensitic stainless steel. The results showed that both plasma spray and HVOF coating show an even deposition, which could not be achieved by a flame spray method. Those three coatings meet manufacture minimum bond strength requirements. The highest bond strength and hardness were provided by the HVOF process with a value of 33.1 MPa and 719 HV, respectively. According to bond strength and standard hardness deviation, the HVOF process gives the most homogeneous coating. Substrate hardness just below the coating interface after flame spray, plasma spray, and HVOF process are raised by 236%, 56%, and 65% each from the specification. HVOF coating has the best cross section compared to others. Smallest porosity percentage, porosity size, and average interface unbonding is got by the HVOF process, with a value of 0.2%, 7.2 um, and 31%, respectively. Coating microstructure after etching shows phases related to heat input during application. The dendritic structure is observed on flame spray and plasma spray coating after etching but not on HVOF coating. Oxides and carbides of both cobalt and chrome are formed in the coating.