Orientation-dependent creep behavior and microstructure of nickel solid solution single crystals

The creep behavior at 1123 K and the microstructure of undeformed and creep deformed single-crystal specimens of two nickel-based solid solution alloy s with various orientations has been investigated. One of the alloys has th e composition of the matrix of superalloy CMSX-4, but during high temperatu re exposure a volume fraction of about 10% gamma' phase precipitates. This alloy shows an orientation-dependent ratio of the stationary strain rate at 1123 K and 200 MPa of (epsilon) over dot(ss)([001]):(epsilon) over dot(ss) ([011]):(epsilon) over dot(ss)([111]) = 60:50:1. In comparison, a single-ph ase solid solution alloy with nearly the same composition, but without the gamma' forming elements (Al, Ti, Ta), is found to have the dependence (epsi lon) over dot(ss)([001]):(epsilon) over dot(ss)([011]):(epsilon) over dot(s s)([111]) = 2:5:1 at 1123 K and 50 MPa. The stress state of matrix channels in superalloys can be estimated by extrapolating the stress-dislocation de nsity correlation from the particle-free alloy. At all observed specimen or ientations, octahedral glide is dominating. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.