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' superalloy single crystals is experimentally investigated and analyzed according to a description of crystal hardening at the dislocation density and interaction scale, and regardless of the two-phase nature of the material. A matrix of hardening coefficients is estimated from monotonous 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 systems. The estimated interactions between these system pairs separate, within each of the three system groups, a coplanar (including self interaction) coefficient with a non coplanar one. As a whole, the superalloy single crystal hardening anisotropy at this medium temperature comes out comparable to one of the most anisotropic pure f.c.c. metals, mainly 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 quantitative estimates are limited by the questionable assumption of homogeneous behaviour for such a two-phase crystal structure. Analyses accounting For both the crystalline structure and the two-phase nature of these superalloys will be the purpose of the forthcoming Part II.