Effect of Surface Conditions on Room‐Temperature Ductility of Ionic Crystals

Abstract

With the progress on dislocation theories and a better understanding of flow phenomena, it was predicted that a class of materials normally considered to be brittle, namely, ionic solids having cubic crystal structures, would possess a degree of ductility. Experimental results on a number of ionic materials indicate that face‐centered cubic and body‐centered cubic ionic materials can exhibit a considerable amount of ductility under controlled conditions. It was found that these materials are inherently ductile rather than brittle and that there appear to be two factors, a surface reaction with components of the air and impurity concentration, that exert control over the ductility. The examination of the air embrittlement indicated that oxygen and nitrogen are the cause of decreased ductility in water‐soluble salts such as KC1 and KBr. The effect on the surface can be inhibited by surface treatment or by immersion in oil. Other materials such as MgO and LiF do not seem to exhibit a surface embrittlement. MgO does, however, show a time‐dependent ductility that is attributed to the presence of impurities.