Dislocation nucleation during nanoindentation in a body-centered cubic TiZrHfNb high-entropy alloy

Pop-in behavior of a single-phase, body-centered cubic TiZrHfNb high-entropy alloy was characterized using instrumented nanoindentation. The critical shear stress required for the first pop-in was close to the theoretical strength, indicating it was controlled by dislocation nucleation. Data were collected and analyzed using a model based upon the transition-state theory and Weibull statistics. The activation volume for the pop-in events was evaluated to be about 3–5 atomic volumes, much larger than that in pure metals (~one atomic volume), suggesting cooperative migration of multiple atoms. The activation energy was also estimated and compared favorably with the nucleation of a full-dislocation.