PRE-CREEP STRAIN ON SINGLE-CRYSTAL NI3AL

Combination tests involving both constant strain-rate deformation and creep have been carried out on single crystal Ni3Al(Ta 0.5%) with comp ression axis [15 5 (1) over bar]. Specimens were pre-strained 3% at co nstant strain-rate (similar to 10(-4) s(-1)) at room temperature (RT) and at 520 degrees C (just below the peak temperature of Bow stress vs temperature T-p) respectively. Subsequently, both pre-strained specim ens were subjected to creep at the same stress level, 330 MPa, and tem perature, 520 degrees C. After the combination tests, slip trace analy sis was performed and dislocation structures were examined by transmis sion electron microscopy (TEM). The results suggest that not only pre- creep strain, but also the temperature of pre-creep deformation, affec t the subsequent creep. It was found that specimens pre-strained at ro om temperature had a lower creep resistance while those pre-strained a t 520 degrees C had a higher resistance than virgin specimens crept un der the same conditions, although the operative slip systems were the same and quite similar dislocation structures were observed. (C) 1997 Acta Metallurgica Inc.