Microstructure and fatigue damage mechanism of Fe Co-Ni-Al-Ti-Zr high-entropy alloy film by nanoscale dynamic mechanical analysis

Micro-electromechanical system (MEMS) films are subjected to a large number of impact during the working process. The fatigue life of the films need be measured to evaluate the reliability of the film's impact resistance. In this work, a new kind of MEMS soft magnetic non-equimolar high-entropy alloy (HEA) film (Fe-Co-Ni)(25)(Ti-Zr-Al)(75) was prepared by magnetron sputtering. The fatigue damage behaviors of the HEA film was investigated by nanoscale dynamic mechanical analysis (nanoDMA) technique. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM) were adopted to analyze the microstructure and damage surfaces pattern. The results showed that the HEA film displayed a polycrystalline structure with the fcc solid solution uniformly distributed in the amorphous phase. There were three stages during the process of fatigue damage, the compressional deformation stage, the buckling and layering stage, and the edge crack propagation leads to the delamination stage. The contact stiffness suddenly decreased at the moment of fatigue damage happening.