In-situ TEM observations of nanovoid initiation and crack evolution in FCC phase of AlCoCrFeNi2.1 eutectic high-entropy alloy

Abstract

The changes in microstructures after the exhaustion of dislocation-gliding ability but before cracking in the face-centered cubic (FCC) phase of AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) were investigated by using in-situ transmission electron microscopy (TEM) tensile tests. It was found that crystal thinning area occurred ahead of the crack tip through dislocation gliding during loading. After that, crystal rotation and/or twinning took place in the crystal thinning area, which were the two main procedures after the exhaustion of dislocation glide ability but before cracking for this alloy. Nanovoids initiate in the dislocation-free zone ahead of the crack tips through crystal rotation induced by local high-stress concentration. Once the high-stress concentration at crack tip overcomes the critical twinning stress, new nanovoids are initiated near the deformation twin through Shockley partial dislocation (1/6 〈112〉 type) glide emitted from the deformation twin. The connection of these nanovoids would lead to the formation of nanocracks. Eventually, the “Y” and “zigzag” crack propagation paths were formed in the FCC phase for AlCoCrFeNi2.1 EHEA.