POST-CREEP STRAIN OF NI3AL AT 380-DEGREES-C

Post-creep strain tests on single crystal Ni3Al have been conducted at 380 degrees C (far below the peak temperature T-p of flow stress) aft er creep at the same temperature. When specimens were crept at about 2 25 MPa (just below the conventional yield stress) for 45 h to a plasti c strain of about 0.5% and then deformed 2% at a constant strain rate (10(-4) s(-1)) at the same temperature, it was found that dislocation structures were different from those observed after constant strain-ra te deformation at the same temperature on annealed specimens. Dislocat ions are mainly on the cube cross-slip plane in the pre-crept specimen s instead of on octahedral planes as in conventional annealed specimen s. The dislocations exhibit quite a curved morphology although screw a nd near-screw segments predominate. Although the dislocations are glid ing on the cube plane, super or double Lomer-Cottrell locks of the edg e segments are not common.