Microstructure characterization of AlxCo1Cr1Cu1Fe1Ni1 (x = 0 and 2.5) high-entropy alloy films

Co20Cr20Cu20Fe20Ni20 (at.%) (Al-0) and Al33.35Co13.33Cr13.33Cu13.33Fe13.33Ni13.33 (at.%) (Al-2.5) high-entropy alloy films with thicknesses less than 500 nm were successfully fabricated by sputter technique using alloy targets. Their microstructures are characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectrometer, transmission electron microscopy and nanoindentation techniques. It is found that compositions for both films are uniformly in depth. The both as-deposited films are composed of nanometer-sized grains with serious lattice distortion. The as-deposited Al-2.5 film, having a hardness of 15.4 GPa and reduced Young's modulus of 203.8 GPa, exhibits a body-centered cubic structure and remains stable up to 873 K for 20 min whereas the as-deposited Al-0 film, having a hardness of 6.3 GPa and reduced Young's modulus of 87.9 GPa, exhibits a face-centered cubic structure and remains up to 773 K for 20 min. It seems that due to high temperature structure stability and high hardness, the Al-2.5 film could be used as a potential coating material on high-temperature Ni-based alloys.