Investigation of microstructural and tribological properties of different APS coating layers

SUMMARY Atmospheric Plasma Spray (APS) method is a thermal spray coating technology in which coating powders are melted with the electric arc and sprayed onto the substrate material by accelerating it with a plasma jet. In this study, APS coating layers were produced on AISI 304 stainless steel substrate with three different coating powders containing Al2O32.5TiO22SiO2Fe2O3 (Metco 101-NS), Al12Si (Metco 52C-NS), and WC12Co (Metco 71-NS) also an AlNi layer has been added before coating on Metco 101-NS and Metco 52C for good coating adhesion of the substrate. Microstructure, microhardness, and tribological properties of the coatings were examined. Microstructural examinations were performed using optical and scanning electron microscopy (SEM) and EDS analyses. Microhardness measurements were taken from the coating layer inward and mean microhardness values were calculated. Dry sliding wear tests were carried out in accordance with ASTM G99 standards to determine the friction and wear behavior of APS coating layers. The thickness of Al2O3, Al12Si, and WC coating layers were measured as 350µm, 450µm, and 200µm, respectively. Microstructure examinations showed that the coating powders accumulated in a layered structure on the substrate material and as expected, little microstructural defects such as gaps, cracks, etc. were formed. The average microhardness values of the coatings were calculated as 908.2 HV0.1, 204.4 HV0.1, 947.7 HV0.1 respectively. The highest microhardness values were obtained in the WC-containing APS coating. The specific wear rates were calculated by measuring wear channels with a surface profilometer. After the dry sliding wear tests, the wear channels were examined by SEM and EDS analysis, and the wear mechanisms were determined. Keywords: APS, Microstructure, Microhardness, Wear.