JOURNAL DE PHYSIQUE IV

The compressive creep deforrn;~tiort microstructure of polycrystalline Ni3AI h:is been observed by transnlission electron microscopy (TEM). <I 10> ( 1 1 I) rind <I 10> ( 110) slip systems have been identified in primary creep. Dissociatiort of edge superparti:~l pairs perpendicular to the slip plane (both { 11 1) and ( 110) ) is common in crept specimens. I'he formation of this superdislocation configuration is thought to limit the extent of primary creep deforniation. lnt rotluction The creep behaviour of Ni3AI at intermediate temperatures does not display the three typical stages characterised as primary, steady-state and terrir~ry. Instead, after primary creep, the rate continually increases with creep strain [11,12],1.31. A model of the processes controlling the intermediate temperature creep behaviour of Ni3Al has been suggested by Hemker et al 131. In primary creep, the octahedral glide of superpartial dislocation p:rirs, which have;I pl;in;ir dissociation, results in a comparatively high initial creep deformation rate. Subsequently, thermally activated crohs-slip of the screw segnients onto a cube plane to form K-W locks immobilizes the supcrdislocations. This leads to exhaustion of octahedral glide and reduces the strain rate. After the screw segments are locked, the edge segments continue to expand on th