NiCrSiBC coatings: Effect of dilution on microstructure and high temperature tribological behavior

Abstract

Protective coatings for high temperature applications have to exhibit good oxidation resistance and microstructure stability. The effective protection of parts with hardfacing techniques depends on the impact of the substrate on the deposited alloy, typically assessed by dilution. This investigation aims to evaluate the effect of dilution on microstructure and high temperature wear of NiCrSiBC coatings processed by plasma transferred arc on a stainless steel substrate. The microstructure was characterized by EDX, XRD, SEM and hardness. High temperature wear behavior was assessed by ball on disc tests with an alumina sphere sliding against the NiCrSiBC coating. Results showed that an increase on dilution suppressed the formation of Cr5B3 borides reducing hardness. Wear behavior was ruled by the combined effect of dilution and test temperature. The effect of dilution is two fold, altering the microstructure and oxidation resistance. At low wear temperatures, the microstructure rules the performance and harder coatings exhibited a better resistance. At high temperature, wear depends on the tribolayer formed. The low oxidation resistant Fe rich coatings form more debris during sliding. The more compact tribolayer formed under these conditions covers most of the area of the wear track and accounts for the enhanced performance of high dilution coatings.