Fatigue resistance of nanotwinned high-entropy alloy films

Nanotwinned nanocrystalline CoCrFeNi high-entropy alloy films were prepared by magnetron sputtering. A disordered face-centered cubic structure was identified, with a uniform distribution of chemical elements. Both <1 1 0> out-of-plane and <1 1 1> in-plane textures were also observed in the nanotwinned film with a thickness of 2.98 mu m. The fatigue resistance of the films was analyzed by nanoindentation technique with up to 103 cycles under various impact energies, complemented by post-test atomic force microscopy investigation of indentation craters. Unlike coarse-grained samples, the nanotwinned films exhibited excellent fatigue resistance, characterized by history-independent and near-stable fatigue responses. Under the influence of the textures developed in the films, the nanotwin planes were oriented toward the loading direction under each fatigue cycle. As such, extremely stable correlated necklace dislocations structure formed and moved back and forth along the twin boundaries during cyclic loading, which preserved the slip systems as well as the coherency and stability of twin boundaries.