HARDENING ANISOTROPY OF GAMMA GAMMA' SUPERALLOY SINGLE-CRYSTALS .1. EXPERIMENTAL ESTIMATES AT 650-DEGREES-C FROM A HOMOGENEOUS ANALYSIS/

The hardening anisotropy, in quasi static loading, of gamma/gamma' sup eralloy single crystals is experimentally investigated and analyzed ac cording to a description of crystal hardening at the dislocation densi ty and interaction scale, and regardless of the two-phase nature of th e material. A matrix of hardening coefficients is estimated from monot onous and sequential loadings at 650 degrees C on [001], [011], [111] oriented samples of two different alloys with similar compositions and structures. This hardening analysis distinguishes three types of slip systems ail having the [110] type slip direction: octahedral systems with an easy or an uneasy dislocation motion direction, and cubic syst ems. The estimated interactions between these system pairs separate, w ithin each of the three system groups, a coplanar (including self inte raction) coefficient with a non coplanar one. As a whole, the superall oy single crystal hardening anisotropy at this medium temperature come s out comparable to one of the most anisotropic pure f.c.c. metals, ma inly because of the hardening asymmetry on the octahedral systems. If the asymmetry is averaged, the remaining anisotropy falls down to the anisotropy level of high stacking fault energy f.c.c. metals. These qu antitative estimates are limited by the questionable assumption of hom ogeneous behaviour for such a two-phase crystal structure. Analyses ac counting For both the crystalline structure and the two-phase nature o f these superalloys will be the purpose of the forthcoming Part II.