Effect of substrate temperature on the formation of nanotwin and properties of NiCoFeCrAlTi high-entropy alloy thin films

In this study, magnetron sputtering was utilized to deposit Ni30Co30Fe13Cr15Al6Ti6 high-entropy alloy thin films (HEAFs) at various substrate temperatures, ranging from 25 ◦C to 400 ◦C. When the substrate temperature is below 200 ◦C, the HEAFs show columnar structure with nearly 100 % (111)-oriented face-centered cubic (FCC) phases. The growth nanotwins are also observed with an average twin thickness below 2 nm. When the substrate temperature exceeds 200 ◦C, the columnar structure gradually transforms into a dual-phase body-centered cubic (BCC)+FCC polycrystalline structure accompanying the disappearance of nanotwins. The nanotwinned HEAFs

deposited at below 200 ◦C exhibit high hardness (> 10.5 GPa) and low roughness (Rms <0.58 nm). When the substrate temperature exceeds 200 ◦C, the hardness of HEAFs decreases and the roughness becomes higher. The residual stress also shifted from compressive stress to tensile stress with rising substrate temperatures.