HIGH-TEMPERATURE CREEP-BEHAVIOR IN NI-3(AL, TA) SINGLE-CRYSTALS WITH DIFFERENT ORIENTATIONS

High temperature creep behavior of a nickel-rich Ni-3(AI, Ta) with the Ll(2), structure is investigated in order to clarify the influence of crystallographic orientation. The single crystals with four different orientations are deformed in compressive creep at the temperatures ra nging from 1123 to 1273 K under a constant load with initial shear str esses being from 35 to 120 MPa for the (111)[(1) over bar 01] slip sys tem. The results show a distinct orientation dependence of creep stren gth, although shape of creep curves, stress exponent and the activatio n energy seem to be independent on orientation. It is shown, however, that the internal stress measured by strain transient dip tests is fou nd to be orientation-dependent and that the creep behavior is independ ent on orientation if these are analyzed with the effective stress ins tead of the applied shear stress.