Effect of Zr addition on microstructure and mechanical properties of CoCrFeNiZr_x high-entropy alloy thin films

As the technology of microscale devices evolves to smaller dimensions, the newly surged high-entropy alloys (HEAs), in particular high entropy alloy thin films (HEAFs), manifest excellent properties for practical applications. However, limited studies to date focused on microstructures and their impact on mechanical properties of HEAFs. In this work, we systematically investigated the relationship between microstructure and mechanical properties of CoCrFeNiZr_x (x = 0, 0.3, 0.5, 1) high-entropy alloy thin films. A transition from single-phase crystal to amorphous structure was observed with increasing Zr concentration from 0 to 20.7 at.%. In the intermediate Zr concentration ranging from 7.0 to 12.9 at.%, Zr addition renders a crystal–amorphous dual-phase structure with Zr element segregation and a peak hardness of 6.7 GPa. These findings not only provide deep insight into understanding alloying effects on microstructure evolution and mechanical properties of HEAFs, but also present valuable information for designing ultrastrong high-entropy alloys for practical applications, such as microelectronic devices, lightweight lattices and advanced coating industry.