Phase evolution and solidification cracking sensibility in laser remelting treatment of the plasma-sprayed CrMnFeCoNi high entropy alloy coating

The mechanism of solidification cracking in a laser-remelted bead of a plasma-sprayed CoCrFeMnNi high-entropy alloy coating was revealed. The oriented dendrite growth and phase distribution of the remelted bead were characterized by electron backscatter diffraction, which indicated that the center of this local site consisted of parallel columnar grains. A face-centered cubic phase (FCC) and body-centered cubic phase (BCC) existed in the fusion zone. Under solidification shrinkage, the columnar dendrites detached from each other, which yielded the necessary strain factor to generate solidification cracks. Because of the different dilution rates for different parameters, the laser-remelted zone presented three solidification modes (including the full FCC mode, the FCC-BCC mode and the BCC-FCC mode) for different process parameters, which presents different cracking sensibilities. The samples that were solidified in the full FCC and BCC-FCC mode presented no cracks in the fusion zone. The laser-remelted bead exhibited cracking only for the FCC-BCC solidification mode under a specific composition. The phase-diagram calculation showed that the less secondary solid phase (BCC phase) formed during the end of the solidification within the fusion zone, the higher cracking sensibility of the samples. The remnant liquid film existing in the inter-dendrites region weakened the bonding between each dendrite, which triggers the cracking under thermal stress. (C) 2019 The Authors. Published by Elsevier Ltd.