HARDENING AND STRAIN-AGING BY VACANCIES AND THEIR AGGREGATES IN FEAL

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. Vacan cies, probably present as submicroscopic aggregates, can act as streng thening obstacles to subsequent dislocation movement. When the vacanci es are present in the form of somewhat coarser aggregates or dislocati on loops they may act both as dislocation obstacles and vacancy source s during subsequent deformation at intermediate temperatures. The stre ngthening obtained depends sensitively on the precise vacancy aggregat e present. In addition, such vacancy aggregates can lead to significan t dynamic dislocation locking and the appearance of both static and dy namic strain ageing phenomena.