The role of phosphorus in a newly developed Ni-Fe-Cr-based wrought superalloy

The influence of phosphorus on the microstructures and mechanical properties of a newly developed Ni-Fe-Cr-based wrought superalloy (named as HT700 alloy) for ultra-supercritical power plant applications beyond 700 °C was investigated. Results showed that adding phosphorus significantly prolonged the creep rupture life but had little influence on the yield strength of HT700 alloy when phosphorus content ranged from 0.002 to 0.027 wt%. Meanwhile, intergranular failure mode dominated in all creep ruptured samples while transgranular failure was the main feature in the tensile tested samples. The effects of adding phosphorus on the nucleation and growth behavior of intergranular M23C6 carbides were found to be the main mechanism responsible for the difference.