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 mu phase and M23C6 carbide on microstructure and creep properties of DD5 single-crystal superalloy during long-term thermal exposure at 1000 degrees C were investigated in detail. It was found that during thermal exposure at 1000 degrees C, the needle-like mu 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 1038 degrees C/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 (M2C6)-C-3 particles, while that exposed for 1000 h was reduced by 60% due to the precipitation of more mu phase and degradation of.' phase. Furthermore, tensile stress could also promote the precipitation of mu phase and M23C6 carbide.