Effect of precipitation behaviour of μ phase and M₂₃C₆ carbide on microstructure and creep properties of DD5 single-crystal superalloy during long-term thermal exposure

The effects of μ phase and M23C6 carbide on microstructure and creep properties of DD5 single-crystal superalloy during long-term thermal exposure at 1000°C were investigated in detail. It was found that during thermal exposure at 1000°C, the needle-like μ phase and granular M23C6 carbide were mainly precipitated in dendrite arm and interdendritic regions, respectively. The amount of precipitated phases rose with increasing exposure time. Under the condition of 1038ºC/172 MPa, compared with the sample after standard heat treatment, the creep life of sample exposed for 500 h was increased by 38% due to the precipitation of a large number of M23C6 particles, while that exposed for 1000 h was reduced by 60% due to the precipitation of more μ phase and degradation of γ′ phase. Furthermore, tensile stress could also promote the precipitation of μ phase and M23C6 carbide.