The deformation of a model metal-ceramic material; Nb-ZrO₂ single crystals

Abstract

Surface slip lines on specimens prepared and deformed as described in Part I were examined by Nomarski interference contrast and by transmission electron microscopy of sections crystallographically oriented with respect to the active slip systems. No slip lines were visible on any specimens after deformation at 113 K and 175 K and, at higher temperatures, faint slip lines were found only in the alloys of higher zirconium content. At low temperatures, slip was coarse but was usually on the expected primary plane or on ; anomalous slip was not observed. At the lowest temperatures, 40 K and 4·2 K the initial deformation was always by twinning. Various secondary slip planes were observed after small deformations at low temperatures and the conjugate slip system operated after high strains at all temperatures.

The dislocation structures resembled those of pure b.c.c. metals inasmuch as the majority of dislocations were screw type at low temperatures and non-screw type at higher temperatures. However, another feature of the deformed structures at most temperatures were long rows of prismatic dislocation loops formed by interaction of dislocations with ZrO₂ particles and aligned along the direction of the primary Burgers vector. Prismatic loops were not observed at temperatures where deformation was mainly by twinning and there were few loops per particle at room temperature and above. Although these loop structures were similar to those frequently observed in f.c.c. metal matrices, their influence on the flow stress and work-hardening rate was relatively small. Possible reasons for this are discussed.