Phase transition zones in compositionally complex alloy films influenced by varying Al and Ti content

Abstract Phase changes due to compositional variation of alloying elements in the AlCrFeNiTi and AlCoFeNiTi families of compositionally complex alloys (CCAs) were investigated by employing magnetron co-sputtering synthesis techniques and microstructural characterization via scanning electron microscopy, X-ray diffraction, and energy dispersive X-ray spectroscopy. Compositional alterations were introduced by varying the input power provided to either an Al or Ti target, as well as by the substrate quadrant location. A synergistic relationship between Al and Ti was observed in which both elements compete to drive phase formation, and was revealed to be further influenced by substituting Cr with similarly sized, but structurally dissimilar, Co. The crystallinity of the studied samples was mapped with respect to Ti and Al content to emphasize the distinct compositions where phase transitions occur for each CCA family. Nanoindentation was employed to study how different phases affect the mechanical properties, with results indicating that amorphous samples generally exhibited lower hardness and moduli when compared to the crystalline and “mixed” phase samples. This work highlights how sputtering can be used to control individual elements within CCA families in order to examine how their atomic characteristics contribute to phase formation and crystallinity.