TEMPERATURE-DEPENDENCE OF STRAIN-RATE SENSITIVITY, WORK-HARDENING ANDDISLOCATION-STRUCTURE IN NI3AL SINGLE-CRYSTALS

Ni3Al single crystals have been deformed at 77, 292 and 500 K and at d ifferent strain rates. Dislocation structures in the deformed specimen s have been examined by high-voltage electron microscopy. It is found that the structures depend strongly on test temperatures even at small strains such as 1%. The anomalous strengthening in the present alloy is thus attributed to be of a structural origin, particularly at high temperatures. It is also shown that flow stress is independent of stra in rate both at 77 K and at 500 K while a weak strain-rate dependence appears at room temperature. On the basis of these observations, a pos sible mechanism of thermal and athermal strengthening is proposed by t aking account of the work hardening and the structural change.