Exhaustion Hardening in Mo-alloy Nanofibers

The evolution of defects in Mo alloy nanofibers with dislocation densities ranging from 0 to ~1x10(14) m(-2) were studied using an in situ "push-to-pull" (PTP) device in conjunction with a quantitative nanoindenter in a transmission electron microscope (TEM). By augmenting the in situ testing method with Digital Image Correlation (DIC), we can determine the true stress and strain in local areas of deformation. With no initial dislocations, the Mo-alloy nanofibers suffered sudden catastrophic elongation and softening at ultrahigh stresses. On the other extreme, fibers with a high dislocation density operated with sustained homogeneous deformation, but failed at lower stresses. Between these two extremes nanofibers with intermediate dislocation densities demonstrated clear exhaustion hardening behavior, where the progressive exhaustion of dislocations increases the stress required to drive plasticity.