Formation mechanism of M23C6 around NbCrN and its effect on fatigue behavior for a novel 25.5Ni-23.5Cr-3W-3Cu-1.5Co alloy

Abstract

The formation mechanisms of M23C6 precipitates around NbCrN precipitate of 25.5Ni-23.5Cr-3W-3Cu-1.5Co heat resistant alloy were studied, and their influence on the low cycle fatigue at 700 °C was discussed. The results show that when the strain rate (ε˙) increases, the plastic strain amplitude, first decreases and then increases. This variation trend is related to the distribution of M23C6 precipitate. At ε˙=4×10−3 s−1, when the number of cycles increases, the NbC is formed around the primary NbCrN precipitates firstly, and then M23C6 is formed at the interface between NbC and matrix. Consequently, the structure of the NbCrN precipitate is surrounded by formed M23C6 precipitate, which indicates that the dislocations are earlier to slip owing to the smaller stress concentration. Therefore, the plastic strain amplitude is larger. At ε˙=2×10−3 s−1, the tangle effect of dislocations on NbCrN precipitate leads to a higher stress concentration around the NbCrN precipitate, which can promote the nucleation of M23C6. Therefore, the dislocations are not easy to slip, which indicates that plastic strain amplitude is smaller.

Keywords

• M23C6 precipitate
• Strain rate
• Low cycle fatigue
• Plastic strain amplitude
• Heat resistant steel