Incipient plasticity and dislocation nucleation in body-centered cubic chromium

In this study, we conducted nanoindentation tests to explore the incipient plasticity (or onset of yielding) in a fully annealed coarse-grained Cr at loading rates between 0.02 and 2 mN/s and temperatures ranging from 295 to 423 K. The maximum shear stress at the first indentation pop-in were evaluated and found comparable to the theoretical shear strength for the yielding of dislocation-free Cr. The activation volume and activation energy for the onset of yielding were also evaluated using Schuh׳s statistical model, and further compared with that anticipated for homogeneous and heterogeneous dislocation nucleation processes. We concluded that heterogeneous nucleation was the favorite mechanism and the type of point defect that induced dislocation nucleation appeared to be interstitials rather than vacancies in the body-centered cubic Cr.