Anisotropic stress rupture properties of the nickel-base single crystal superalloy SRR99

The influence of orientation on the stress rupture properties of a single crystal superalloy SRR99 was investigated at temperatures of 760 and 1040 °C. It is found that the creep anisotropic behaviour is pronounced at the lower temperature of 760 °C and the stress rupture life ranks in the order [0 0 1] > [1 1 1] > [0 1 1]. Despite the anisotropy of stress rupture life is evidently reduced at the higher temperature, the [1 1 1] orientation exhibits the longest life. At 760 °C, EBSD (electron back scattered diffraction) was adopted to measure the lattice rotation and the deduced results indicate that the dominant slip systems are 〈1 1 2〉 {1 1 1} during stress rupture test. At 1040 °C, the ranking order of the stress rupture life is [1 1 1] > [0 0 1] > [0 1 1] and the single crystal close to [0 1 1] orientation still shows the poorest life. In the [0 0 1] and [1 1 1] samples, regular γ′ raft structure is formed compared with [0 1 1] samples. Further observations made by TEM investigations reveal the underlying deformation mechanisms for crystals with orientations near [0 0 1], [0 1 1] and [1 1 1] under two test conditions.