Influence of Machining Surface Finishing on Cavitation Resistance of a GWAW Deposited Cobalt Austenitic Stainless-Steel Coating

Abstract The cavitation phenomenon represents a serious efficiency problem for hydro generators. Long repair periods associated with a total equipment stoppage have a significant impact on the effective cost of turbine maintenance. Welding is followed by grinding finish, and depends on the operator’s skill, which can cause significant changes in the profile of the component, as well as in its roughness. Low values of roughness in the recovered surface can reduce the loss of mass by cavitation. Understanding the cavitation phenomenon, associated with the surfaces obtained by different machining conditions, can promote a better understanding of wear mechanisms related to cavitation on machined surfaces. This article has evaluated the mass loss and the roughness profiles produced by different conditions of machining in a cavitation resistant austenitic stainless-steel coating, deposited on to martensitic stainless steel. Polished and ground samples were used as surface condition references. The results indicated that the surface finish obtained by machining influences the cavitation process, mostly in the incubation stage. The cavitation mass loss occurs mainly through pitting mechanisms in micro-burr regions with detachment of adhered material, resulting from machining conditions. As for the evolution of the roughness throughout the experiments, the polished, ground and machined samples showed different behaviors.