Effects of Ni-P amorphous films on mechanical and corrosion properties of Al0.3CoCrFeNi high-entropy alloys

Through electroless plating, the Al0.3CoCrFeNi high-entropy alloys were successfully coated with the Ni-P amorphous film with a thickness of 1.2 μm. For studying the surface change of samples after chemical plating, the surface morphologies of the as-cast HEA substrate and HEA with the Ni-P film were contrasted by atomic-force microscopy. The tensile properties of the samples with and without the Ni-P film, and the deformational behavior of thin Ni-P film were researched, respectively. In addition, the effect of the Ni-P amorphous film on corrosion resistance of the coated HEAs was also investigated. The experimental results show that in contrast to the uncoated samples with a yielding strength of 275 MPa, the yielding strength of the coated samples exhibits 400 MPa, with a 45% improvement, which can be attributed to the very high yield strength of the Ni-P amorphous film. A tensile strain up to 10% was achieved in the Ni-P film since the propagation of one primary shear band was inhibited, and the stress/strain concentration was retarded by the plastic substrate. The corrosion resistance of the HEA with the Ni-P film is superior to that of the bare HEA in the 3.5 wt percent NaCl solutions due to the chemical homogeneity and the absence of microscopic defects in the Ni-P amorphous film. The current results indicate that the surface coating is an effective means for optimizing the properties of HEAs, and the thin Ni-P coating can remarkably improve the strength of the present HEAs.