Failure modes after exhaustion of dislocation glide ability in thin crystals

The changes of microstructures after the exhaustion of dislocation glide ab ility but before cracking, as well as microcrack initiation by them, were s tudied in detail by in-situ transmission electron microscopy (TEM) for pure copper, aluminum and iron. Thinning occurred in the thicker regions throug h dislocation gliding in the three metals. After that, {111} [112] twinning or tensile cracking took place in thinned zones in fee metals. In the case of twinning, new microcracks were initiated along another {111} plane by t he high stress concentration near the growing tip of the twin, while in iro n (bcc), many nanocracks were initiated in the thinned areas just ahead of the crack front, resulting in misorientation microstructure from which micr ocracks or microvoids were developed.