Properties of atomized AlCoCrFeNi high-entropy alloy powders and their phase-adjustable coatings prepared via plasma spray process

In this study, the adjustment of the phase constitution of AlCoCrFeNi high-entropy alloy (HEA) coatings was achieved using a plasma spray process with vacuum gas-atomized powders. The as-prepared AlCoCrFeNi powders were of pure BCC phase and the particles were in spherical shape. The FCC phase began to form above 600 °C, and its degree of crystallinity increased with annealing temperature, resulting in a reduced saturation magnetization. Two Curie temperatures were observed in as-atomized powders: the first was around 220 °C and was reversible; the second was contributed by the irreversible FCC phase transformation over 600 °C. When depositing the AlCoCrFeNi coating using the plasma spray process, the ratio of the FCC phase increased with increasing spraying current and argon flow rate. However, the phase constitution of the AlCoCrFeNi coatings was also influenced by powder size. With coarse powders (60–90 μm), the formation of FCC phase was suppressed, even as the current and gas flow were increased to 750 A and 50 l/min, respectively. The physical properties, such as porosity, hardness, and saturated magnetization, of plasma-sprayed AlCoCrFeNi can hence be adjusted by tuning its phase constitution.