Anisotropic Stress Rupture Properties of a 3rd-Generation Nickel-Based Single-Crystal Superalloy at 1100 °C/150 MPa

The influence of orientation on the stress rupture behaviors of a 3rd-generation nickel-based single-crystal superalloy was investigated at 1100 °C/150 MPa. It is found that the stress rupture anisotropy is shown at 1100 °C, but not so obvious compared with that at intermediate temperatures. The [001] specimens display the longest rupture life, [111] specimens show the shortest rupture life, and [011] specimens exhibit the intermediate life. Detailed observations show that the final fracture is caused by crack initiation and propagation, and the anisotropy of three oriented specimens is related to the fracture modes, γ/γʹ microstructures, interfacial dislocation networks and cutting mechanisms in γʹ phase. For [001] specimens, N-type rafted structures are formed which can well hinder the slip and climb of dislocations. Besides, the regular interfacial dislocation networks can prevent dislocations from cutting into γʹ phase, leading to the improvement of the creep resistance. For [011] specimens, ± 45° rafted structures and irregular networks result in less strain hardening. For [111] specimens, a large number of crack propagation paths and inhomogeneous deformations caused by irregular rafted structures deteriorate the property and result in the shortest life. Furthermore, a[100] superdislocations with low mobility are widely formed in [001] and [011] specimens which suggests the low creep strain rate during steady creep stage, whereas superdislocations in [111] specimens possess high mobility, which indicates the high strain rate and corresponding poor stress rupture property.