Temperature and orientation dependence of elastic and yield properties of single crystal nickel base superalloy

Abstract

Elastic modulus and yield stress measurements have been made in the temperature range 20–1050°C for the nickel base superalloy single crystal SRR99 at several crystallographic orientations. The results indicate that both the elastic and yielding behaviour of SRR99 are strongly dependent on temperature and orientation. The variations in the elastic moduli E with temperature T were different for different crystal orientations. However, the slopes of dE/dT were found to change abruptly at about 650°C for all the crystal orientations. The yield stress as a function of temperature generally exhibited three distinct regions for all the specimen orientations. The tension/compression anisotropy was found to be orientation dependent. The tensile yield stress was higher than for compressionfor specimens near [001], but the reverse occurred for specimens near [111]. Schmid s law did not provide an adequate description for correlating the yield stress as a function of orientation. A cross slip model based on the deformation mechanisms of single crystals was used to explain qualitatively the observed yielding behaviour. Systematic comparison of the elastic and yield stress experimental results for SRR99 with other single crystal and polycrystalline superalloys revealed that these characteristics are common for nickel base superalloys, and can be attributed to the temperature dependent behaviour of the major constituent phases (γ and γ′) of nickel base superalloys.

MST/3149