Effect of plasma remelting on microstructure and properties of a CoCrCuNiAl0.5 high-entropy alloy prepared by spark plasma sintering

A CoCrCuNiAl0.5 high-entropy alloy (HEA) was prepared by spark plasma sintering (SPS). The effect of plasma transferred arc (PTA) remelting on the microstructures and properties of the SPS-ed HEA was studied. The results showed that, after PTA remelting, the microstructures transformed from randomly-oriented equiaxed grains to dendrites with a directional solidified morphology. The coarse plate-like precipitates (~ 130 nm in diameter and ~ 20 nm in thickness) containing ordered L12 and disordered FCC structures inside the matrix grains were replaced by the disordered FCC spherical Cu-rich precipitates with several nanometers within the dendritic matrix. In the intergranular region, the size of the L12 cubic precipitates was decreased from ~ 55 nm to ~ 2 nm, and dislocations and lattice distortions were also observed. In addition, the brittle B2 phase was disappeared, and the extent of Cu segregation was decreased in the interdendritic region. The SPS-ed sample has a compressive yield strength of 913.8 MPa and a fracture strain of 21.7%. However, the PTA remelted sample exhibits a much higher fracture strain (> 70%, without fracture) and an appreciable yield strength of 739.4 MPa, which indicates an excellent balance between strength and ductility was achieved after PTA remelting. Furthermore, the corrosion resistance of the PTA remelted sample was higher than that of the SPS-ed sample, which was mainly due to the decreased elemental segregation, and the reduced sizes and types of the precipitates.