The creep deformations of γ-single phase Ni-20mass%Cr single crystals with stress
axes within standard stereographic triangle and at the three pole positions have been investigated.
The most of the creep life is occupied by the transient stage, which consists of Stage I and Stage II.
In Stage I, the creep rate just after loading remains constant. In Stage II, the creep rate decreases
continuously. Except for the single crystals with stress axes of [001] and [1,–11] poles, the single
crystals make the creep deformation using the primary slip plane of (111). As a result, the cross
section of the specimens turns from circular to elliptical in shape. However, there are marked
difference in deformation manner among single crystals with the stress axes within standard
stereographic triangle. The single crystals whose angle between stress axis and primary slip plane
of (111), θ. is more than 45° shows the heterogeneous deformation during creep. While, the
homogeneous deformation will be expected in the single crystals with θ less than 45°. In this
study, by using the four single crystals with θ less than 45°, the change in the stress axis with the
creep deformation at 1173K-29.4MPa, is investigated and the deformation manner due to the
primary slip plane of (111) is estimated by conducting the creep interrupting tests. In the two
single crystals with stress axes in the standard stereographic triangle where the moving range of θ is
narrow, comparing to the others, the spot of the stress axis in the inverse pole figure moves for <1,–
01> direction by using (111)<1,–01> slip system, and after arriving at the [001]-[1,–11] line, the
spot turns to its direction for [1,–11] pole using (111)<1,–10> slip system. While, in the other two
single crystals whose stress axes located in the area with wider moving range of θ, the spot of stress
axis only move for <1,–01> direction. And, the widely spread spot of the stress axis is confirmed
after subjecting the small strain.