Effect of graphite addition on the microstructure, hardness and abrasive wear behavior of plasma sprayed NiCrBSi coatings

Plasma sprayed coatings have been considered as one of the important surface modification processes to improve the tribological properties of materials used in extreme conditions. NiCrBSi composite coatings on stainless steel are known to offer good abrasive wear resistance in service conditions. Graphite is the material which has many potential advantages when processed and used in different forms. This paper describes the effect of graphite addition on the microstructure; hardness and abrasive wear behavior of plasma sprayed NiCrBSi coatings. The mechanical and tribological properties of the coatings can be significantly improved by refinement of grain structure of the coatings. The XRD results show that the NiCrBSi-graphite composite coatings are mainly composed of γ-Ni, CrB and Cr7C3. With addition of graphite, phases such as CrB, Cr7C3 emerge in composite coating. The study was conducted, using an abrasive wear test rig according to ASTM G65 on uncoated as well as coated SS304 samples at room temperature. The samples were analyzed for volume loss and wear rate with respect to increasing content of graphite in the coatings. The results suggest that addition of graphite in the coatings resulted in reduction of volume loss and wear rate significantly. The NiCrBSi-8 wt %C composite coating presents excellent abrasion resistance.