Comparison of incipient plasticity in bcc and fcc metals studied using nanoindentation

Using nanoindentation, the incipient plasticity or early stages of dislocation activity has been studied for two bcc metals of different hardness, tungsten and iron, as well as fcc nickel. The deformation behavior of these metals has been probed using indenters of two different geometries, a Berkovich and a cube corner. From a critical analysis of the load–displacement curves, the initial displacement burst, often associated with the initiation of dislocation activity, was found to occur at values close to the theoretical shear stress of the material. Furthermore, the nature of these displacement bursts appears to vary both as a function of strain rate as well as the geometry of the indenter used during the nanoindentation experiments.