Effects of Vacancies on the Onset of Plasticity in Metals-An Atomistic Simulation Study

As strength of crystalline materials strongly depends on their ability to nucleate new dislocations or move the existing ones, a proper knowledge of factors that play a major role at the first stages of plastic deformation is highly desirable. However, fundamental understanding of the role of point defects, such as vacancies or inclusions, on the onset of plastic deformation in otherwise defect-free solids is still lacking. In this work, atomistic simulations are applied to study the role of vacancies in the inception of plasticity in metals. In particular, the effect of single vacancy as well as different vacancy distributions on the onset of plastic deformation in Ni single crystal during the nanoindentation test is explored. The combined effect of vacancy concentration and temperature on the onset of plasticity is also studied. The increase in vacancy concentration typically results in a decrease of load at the onset of plasticity. However, it is found that this is not always the case, and a particular location of one vacancy can be more important for the onset of plasticity than the higher total number of vacancies distributed in the crystal. It is also found that at higher temperatures, the effect of vacancy concentration on the load at the onset of plasticity is less pronounced than at low temperature.