Abstract: In this work, effects of phosphorus addition on high-temperature tensile properties at 650 °C and 650 °C/873 MPa stress rupture properties of nickel-based superalloys containing rare earths (RE) have been investigated. Through experimental characterization and first-principles calculations, the synergistic mechanism between phosphorus and RE elements was elucidated. Results demonstrate that with a phosphorus content of 0.01 wt.%, the stress rupture lifetime of the alloy significantly increased from 25 h to 55 h, with elongation improved from 9% to 12%. Simultaneously, the addition of phosphorus greatly enhanced the high-temperature tensile elongation, from 34% to 44% while the high-temperature tensile strength remained at around 1240 MPa. The main reason is that phosphorus and RE elements co-segregate at grain boundaries, forming RE phosphides. This reduces grain boundary energy and enhances the stability of grain boundaries, thereby hindering intergranular crack propagation and pinning grain boundaries, which collectively improves high-temperature performance. Furthermore, phosphorus reduces the stacking fault energy of the alloy, promoting the formation of microtwins and enhancing strain accommodation capacity, which further improves plasticity. These findings provide theoretical support and technical guidance for the design and engineering application of RE-modified nickel-based superalloys.

Key words: Nickel base superalloy, Phosphorus, Rare earth elements, Grain boundary precipitation, Stress rupture property