The Thickness Dependence of Plastic Behaviors of Copper Whiskers

Abstract

Stress-strain curves of 150 copper whiskers, whose thickness ranges from 4 to 30μ and growth orientations are parallel to the three principal crystallographic orientations, have been investigated by an Instron-type tensile machine at room temperature. Thinner whiskers have shown characteristic sharp yield points. The upper yield stress of some thinner whiskers reaches nearly the theoretical strength of an ideal perfect crystal, but it decreases as the thickness increases. In the subsequent “easy glide” region, corresponding to the propagation of one or a few Lüders bands, pronounced serrations appear, and both of flow stress and Lüders strain vary approximately in inverse proportion to the thickness. The hardening rate in the most rapid hardening stage of the stress-strain curve increases with increasing thickness. In whiskers, thicker, than about 20μ, the sharp yield point and serrated “easy glide” region are scarcely observable, and their Stress-strain curves are similar to those of bulk crystals.