Change in Stress Axis with Creep Deformation in γ-Single Phase Ni-20mass%Cr Single Crystal within Standard Stereographic Triangle

Abstract

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.