Orientation and temperature dependence of slip in iron single crystals

Abstract

The orientation and temperature dependence of slip in ZrH2-purified iron crystals have been investigated at strains up to about 15 pct. Both {110} and {112} slip planes were observed at all temperatures investigated (295°, 250°, 195°, and 143°K) when the orientation of a crystal was such that its maximum resolved shear stress plane (MRSSP) corresponded to {110} or {112}. At 195° and 143°K {110} and {112} slip planes were also observed for orientations where the MRSSP deviated from {110} or {112} slip planes were also observed for orientations where the MRSSP deviated from {110} or {112}. At 295° and 250°K, the slip planes of crystals whose MRSSP was not {110} or {112} deviated from the MRSSP toward {110}. The variation in the intensity and waviness of the slip traces with orientation suggested that cross slip was easiest for orientations that slipped on a {112} plane in the twinning sense (near [001]), and hardest for orientations that slipped on a {112} plane in the antitwinning sense (near [011]). This appears to be in accord with observations of easier dislocation multiplication for orientations near [001] than for orientations near [011]. At 143°K the critical resolved shear stress law was not obeyed; the resolved shear stress was about 14 pct lower for slip on a {112} plane when the sense of the applied stress was favorable for twinning than when it was unfavorable. The slip line observations and the asymmetry of slip on a {112} plane appear to be qualitatively explainable in terms of dissociated dislocation models that are based on differences in the ease with which slip and cross slip can occur on {110} and {112}.