Nanostructured nitride films of multi-element high-entropy alloys by reactive DC sputtering

Multi-element high-entropy alloys (HE alloys) are new alloys with over five principal elements each having an atomic percentage no more than 35%. Using the alloys, e.g. Al0.5CoCrCuFeNi, Al2CoCrCuFeNi, and AlCrNiSiTi, as target materials in reactive sputtering, nanostructured metallic and nitride films were deposited. XRD patterns show that the alloy films of AlxCoCrCuFeNi are crystalline with structures of simple fcc or mixed bcc + fcc solid solution, and the crystallinity decreases and approaches an amorphous structure with increasing nitrogen flow rate into the processing chamber. Unlike the AlxCoCrCuFeNi HE alloys, the metallic film of AlCrNiSiTi is amorphous and its hardness is much higher than the hardest nitride films of AlxCoCrCuFeNi alloy. TEM, FESEM and AFM observations show that the films morphology and structure evolution with N2/Ar fraction is different between AlxCoCrCuFeNi and AlCrNiSiTi HE alloys. The slope of films resistivity versus N2/Ar ratio is much steeper in AlCrNiSiTi than in AlxCoCrCuFeNi HE alloy. The hardness enhancement in nitrides is less significant in AlCrNiSiTi than in AlxCoCrCuFeNi HE alloys.