CALPHAD-guided design and experimental optimization of NiCo-based superalloys with enhanced γ′ phase stability and mechanical performance

This study aims to achieve superior high-temperature mechanical properties in disk superalloys through two approaches: (i) CALPHAD-based design and fabrication of a Co–50Ni–10Al–6Ta–8Cr alloy with a high γ′ dissolution temperature, and (ii) microalloying with tungsten (W) and boron (B) to further enhance mechanical strength and phase stability. The addition of W effectively suppressed the γ′ phase coarsening rate, thereby improving γ′ phase stability. In contrast, B primarily enhanced grain boundary strength, resulting in excellent high-temperature yield strength. The developed Co–50Ni–10Al–6Ta–8Cr–2W-0.085B superalloy exhibits a γ′ coarsening rate comparable to that of the CMSX-4 superalloy. It demonstrates excellent comprehensive performance, with a high γ′ dissolution temperature of 1260 °C and outstanding yield strengths of 1304 MPa at 800 °C, 1104 MPa at 900 °C, and 780 MPa at 1000 °C. The high strength originates from Kear–Wilsdorf (K–W) locking and dislocation entanglement, whereas dislocation climb dominates at elevated temperatures. The enhanced high-temperature creep performance is due to the formation of high-density dislocation loops in γ' phase during the creep process. This study provides significant insights for designing high-strength disk superalloys.