Hardening and strain-ageing by vacancies and their aggregates in FeAl

Abstract
Yield stress and ageing discontinuities have been examined in a Fe-43% Al alloy after carefully ageing in an attempt to control the number of excess vacancies and the form of their annihilation aggregates. Vacancies, probably present as submicroscopic aggregates, can act as strengthening obstacles to subsequent dislocation movement. When the vacancies are present in the form of somewhat coarser aggregates or dislocation loops they may act both as dislocation obstacles and vacancy sources during subsequent deformation at intermediate temperatures. The strengthening obtained depends sensitively on the precise vacancy aggregate present. In addition, such vacancy aggregates can lead to significant dynamic dislocation locking and the appearance of both static and dynamic strain ageing phenomena.

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