Dynamic strain aging and serrated flow in MnO

Abstract

The effects of aging on the upper yield stress τupand serrated flow have been studied in MnO single crystals at 900 °C for oxygen partial pressuresρO2of 10−11and 10−7Pa. Aging initially increases τupas a consequence of segregation of aliovalent impurities to dislocations for bothρO2values. For long aging times andρO2= 10-11Pa, serrated flow accompanied by solute softening is observed. The data fit predictions of a Portevin-Le Chatelier model for serrations, but with impurity atmospheres causing softening instead of hardening. This is believed to result from changes in local defect equilibria caused by segregation of impurities with valences greater than two to dislocations.