Microstructure and high temperature erosion behavior of laser cladded CoCrFeNiSi high entropy alloy coating

Abstract

In this study, CoCrFeNiSi high entropy alloy (HEA) coating without pores or slag defects was prepared on 304 stainless steel surface by laser cladding. Thermodynamic parameters of CoCrFeNiSi HEA were calculated. Microstructure and phase composition were analyzed by means of scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Comparative studies on hardness, high temperature erosion and oxidation performances were conducted between the CoCrFeNiSi HEA and Stellite-6 Co-based alloy coatings. The results show that laser cladding CoCrFeNiSi HEA coating was composed of single FCC structure. Typical metallurgical bonding between cladding coating and the substrate was formed. Microhardness of CoCrFeNiSi HEA coating reached to approximately 580HV0.2, which was higher than that of Co-based alloy coating (485HV0.2). There was little surface hardness reduction at 500, 600 and 700 °C for CoCrFeNiSi and Co-based alloy coatings. Erosion tests were conducted using quartz sand particles at 20, 500, 600 and 700 °C with an impact angle of 30, 60 and 90°, respectively. The HEA coating showed comparatively lower erosion rates than Co-based alloy coating under all test conditions. The erosion morphologies of both coatings showed that ploughing and micro-cutting were the two primary erosion mechanisms at oblique impact angles, while the erosion mechanism was replaced by the formation of craters and platelets at normal impact angles. A dense and continuous oxidation film could form on HEA coating at 700 °C which may protect the coating from erosion at high temperature to some extent.