ORIENTATION DEPENDENCE OF CREEP OF NI3AL AT INTERMEDIATE TEMPERATURE

The orientation dependence of creep of single crystal Ni3Al (1 at.% Ta ) has been investigated at an intermediate temperature of 520 degrees C and at a stress of 550 MPa. Steady-state creep was observed for all orientations. The higher the resolved shear stress on the cube cross-s lip plane, the larger the steady-state creep rate. Surface slip line a nd TEM analysis confirmed that for most orientations the dislocations glide on the primary octahedral plane(s) during the primary stage but glide on the cube cross-slip plane(s) during the secondary stage. For the [<(1)over bar 1> 12] orientation, however, the dislocations remain on the octahedral planes. (C) 1998 Acta Metallurgica Inc.