Effect of Ti Microalloying on the Creep Behavior of Ni-Cr-Mo-Based High-Temperature Alloy

This study explored the influence of 2 at% Ti elements addition on the microstructure evolution and compressive creep performance of Haynes 244 (Ni-8Cr-6W-22.5Mo) at 650 °C under 80 ~ 180 MPa stress states. The results indicate that trace addition of Ti can promote the simultaneous formation of C11_b-type and D0₂₂-type long-range-ordered superlattice phases after aging treatment at 650 °C for 120 h. The aged Ti-doped alloy has better creep resistance at 650 °C /80 MPa, and the steady-state creep rate is only 9.17 × 10^-8 s^-1. Under the coupled influence of stress and high temperature, the existence of nanoscale superlattices is also observed after creep in the as-solid alloy. The stress exponent values of Haynes 244 and the Ti-doped alloys at 650 °C are 5.10 and 5.96, respectively, indicating that the dislocation climbing dominated the creep mechanism. The ordering mechanism of C11_b and D0₂₂ superlattices is continuous ordering, and the interface between precipitates and matrix is coherent. These results indicate that Haynes 244 with Ti addition synergistically precipitates nanoscaled C11_b and D0₂₂ superlattices uniformly dispersed in the matrix, which can effectively pin the dislocation movement, achieve good coherency strengthening and precipitation strengthening, and thus improve creep resistance.