Defect structures in single crystal TiC

A transmission electron microscopy study is presented of sub-boundary defect structures in single crystal TiC. Sub-boundaries consisting of organized dislocation arrays and hexagonal networks were observed. The Burgers vectors of dislocations in the sub-boundaries were determined to be 1/2<110>, and the dislocations were approximately on &lcub;111&rcub; planes. Dislocation nodes in hexagonal networks provided preferential sites for nucleation of triangular planar defects. These defects were identified as platelet precipitates of Ti<b>B</b>₂, although it was difficult to distinguish between precipitates and impurity-stabilized stacking faults during the initial stages of the precipitation. The precipitates were bounded by Shockley partial dislocations and resided on &lcub;111&rcub; habit planes. Segregation of impurities to sub-boundaries resulted in unusual platelet configurations involving beak-like extensions on intersecting &lcub;111&rcub; planes. In such cases, the beak-like extensions were bounded by two uncommon partial dislocations: 1/6[114] and 1/6[1_21_] on &b.delta;-(111). Formation of the extensions involved dislocation climb and was driven by elastic constraint exerted by dislocations of the sub-boundary network. The platelet precipitates were successfully removed by multiple-pass zone refinement, although the substructure was unaffected.