Observations on the interaction of dislocations with a migrating interphase boundary

Abstract

Observations of defect generation during the β ( b. c. c.) ⇆ ζ ( h. c. p.) transformation in the AgAl system have been performed by hot stage electron microscopy. Upon cooling, during the β → ζ reaction both the generation and absorption of dislocations are quite active at the transformation front. At high under-cooling, dislocation generation into the ζ phase was observed to be related to a growth accident process. In the β phase, dislocation emission from a migrating β-ζ interface appeared to be associated with the relaxation of transformation strains and was connected with the presence of step-type interfacial defects. During further transformations, the dislocations emitted into the β phase were absorbed within the same boundary at which they had been generated. Transformation induced dislocation emission was found to contribute to the development of a non-uniform interphase boundary migration and a modified boundary morphology at high under-coolings. These observations indicate that the interaction of dislocations with a migrating interphase boundary can have an important influence on the interfacial reaction kinetics during a phase transformation.