DISLOCATION PROCESSES LEADING TO THE STRESS ANOMALY IN B2-TYPE FE-40-PERCENT-AL SINGLE-CRYSTALS

The anomalous stress peak has been examined in Fe-40%Al single crystal s compressed along a direction near [001]. A sharp stress peak is obse rved at 525 degrees C with anomalous strengthening found only about 25 degrees C on each side of the sharp peak. Deformation by < 111 > supe rdislocations at low temperatures is made more difficult near the stre ss peak as the dislocations react to produce short, essentially immobi le < 100 > segments and as edge superdislocations decompose to < 100 > and < 110 > dislocations, poorly mobile at such temperatures. There i s no evidence of superdislocation pinning by extensive cross-slip, by climb, or by interaction with vacancy loops. At temperatures immediate ly above the stress peak < 110 > and < 100 > dislocations move, while at higher temperatures < 100 > dislocations alone ensure deformation. The flow stress falls because of the thermal activation of glide and b ecause of the limited possibilities for dislocation pinning through in tersections and reactions as deformation occurs by < 100 > dislocation s alone. Many processes have been observed in the temperature range en compassing the stress peak and deducing the critical mechanisms is dif ficult. The role of the orientation of the applied stress in determini ng the relative rate of dislocation interactions and glide is emphasiz ed. (C) 1997 Elsevier Science Ltd.