EFFECT OF GRAIN-BOUNDARY ORIENTATION ON CREEP-BEHAVIOR OF DIRECTIONALLY SOLIDIFIED NICKEL-BASE SUPERALLOY (CM-247-LC ALLOY)

The effect of grain boundary orientation on the creep behaviour of a d irectionally solidified nickel base superalloy (CM 247 LC alloy) has b een studied at 1123 K in the stress range 400-500 MN m(-2). The variat ion of minimum creep I ate with orientation in the alloy can be relate d to anisotropic slip and early onset of tertiary creep in specimens w ith inclined boundaries. Transgranular fracture in longitudinal specim ens occurred by cracklike cavity growth along gamma-gamma' rafts which developed in the initial stages of creep deformation. In specimens wi th inclined boundaries, intergranular fracture occurred by cracklike v oid growth and power law creep may have made a significant contributio n to the growth of voids.