Corrosion and cavitation erosion behaviors of laser clad FeNiCoCr high-entropy alloy coatings with different types of TiC reinforcement

Abstract

By using laser cladding (LC), high entropy alloy coatings (HEACs) with FeNiCoCr as the base material and TiC added directly (D-TiC) and in-situ (I-TiC) were created. The phase composition, microstructure, mechanical characteristics, electrochemical corrosion, and cavitation erosion behavior of HEACs were examined in relation to two TiC addition methods, and a thorough investigation of the effects of mechanical characteristics and corrosion resistance on cavitation erosion behavior was conducted. Large clusters of TiC were visible in the D-TiC HEAC, in contrast to the sparse and scattered distribution of them in the I-TiC HEAC. The average grain size of the composite coating substantially fell from 25.7 μm for FeNiCoCr coating to 11.8 μm for D-TiC coating and 9.4 μm for I-TiC coating when TiC were included in the skeleton. The I-TiC composite coating precipitated by nucleation and growth with the maximum average microhardness of 440 ± 6 HV under the combined action of solid solution strengthening, fine crystal strengthening, and second phase strengthening. In 3.5 wt% NaCl solution, the galvanic corrosion between TiC particles and the FCC matrix significantly weakened the corrosion resistance of the D-TiC HEAC, with the Icorr reaching 3.47 × 10−2 ± 0.8 μA/cm2. The I-TiC HEAC exhibited approximately equal corrosion resistance to FeNiCoCr with an Icorr of merely 5.92 × 10−3 ± 0.3 μA/cm2. Varying cavitation incubation periods (IPs) existed in 316 SS and HEACs at the beginning of the cavitation experiment. The mean depth of erosion rate (MDER) of FeNiCoCr, D-TiC and I-TiC coatings was 0.19 ± 0.09, 0.42 ± 0.04, and 0.15 ± 0.02 μm h−1, respectively, which was only 1/5, 1/2, and 1/6 of that of substrate (0.90 ± 0.13 μm h−1). The cavitation surface of 316 SS was full of craters and cracks without any original surface. Meanwhile, due to the weak interfacial bonding strength between TiC/HEA, the cavitation erosion morphologies of D-TiC HEAC contained spallation of large TiC particles. Attributed to its ideal mechanical and corrosion resistance, the I-TiC composite coating demonstrated the best resistance to cavitation erosion.