On lattice defects and strength anomaly of B2-type FeAl

Our studies on lattice defects and strength anomaly in B2 FeAl are reviewed in this paper, including our latest results. Influence of excess vacancies introduced by quenching from an elevated temperature is very important to the mechanical properties of B2 FeAl. Dot-like features and very small dislocation loops, probably formed by the interaction between gliding dislocations and excess vacancy clusters, were observed on the traces of dislocation movement in a thin foil of a water-quenched specimen. It is considered that the formation process of these dot-like features and small loops is closely associated with an excess-vacancy strengthening mechanism. Positive temperature dependence of yield stress is one of the hottest topics in B2 FeAl. It has been revealed by strain-rate change tests and stress relaxation tests that a recovery rate increases with increasing temperature in the range where temperature dependence of yield stress is positive (Stage II). It was observed in TEM that many superlattice dislocations had climb-dissociated configurations in Stage II, and that 〈111〉-type dislocations were predominant even at the peak temperature when a specimen was deformed to a small strain. Based on these results, the climb-dissociation locking is believed to be the major cause for the strength anomaly.