Direct laser deposition cladding of AlxCoCrFeNi high entropy alloys on a high-temperature stainless steel

AlxCoCrFeNi (x = 0.3, 0.6 and 0.85) high entropy alloy (HEA) claddings were produced by coaxial direct laser deposition (DLD) on a 253MA austenitic steel substrate using a mixture of blended elemental powders. The effect of key processing variables on the formation of HEA claddings and the compositional mixing between the deposited layer and the substrate was investigated through a three-level parametric study on laser power, laser scanning speed, laser beam size, powder feeding rate and hatch distance. Using selected parameters, HEA claddings mostly free of defects were successfully manufactured with very minimal dilution. With an increase in the Al mole fraction from 0.3 to 0.6 and 0.85, the HEA claddings displayed an evolution of crystal structure from FCC, to FCC + BCC and BCC, accompanied by an increase in microhardness. The increased Al content also resulted in reduced microstructural stability of the coatings and hence higher level of thermal softening upon isothermal treatment at 1000 °C.