Influence of process parameters on the formation of phases and mechanical properties of plasma sprayed Al₂O₃–Cr₂O₃ coatings

Abstract

Atmospheric plasma spray process is used to develop Al2O3–Cr2O3 composite coating on AISI 1020 steel substrate by spraying mechanically mixed Al2O3–Cr2O3 feedstock material. The influence of hydrogen gas flow rate on the formation of α-Al2O3 phase in the coating is studied. Effect of changing hydrogen flow rate on the mechanical properties (hardness, wear resistance, porosity and surface roughness) of the coating is also judged. Scanning electron micrograph and X-ray diffraction analyses of the coating are carried out for studying the micro-structure and phases, respectively. Rietveld refinement technique is used to quantify the different phases present in the coating. From the results, it is found that α-Al2O3 phase content in the Al2O3–Cr2O3 coating is decreased with increase in hydrogen gas flow rate. The reduction in α-Al2O3 phase content by the increase in hydrogen flow rate is mainly due to the rise in enthalpy of plasma, causing improvement in the melting of the Al2O3 particles.