A multi-component diffusion multiple approach based synergistic regulation of γ' phase stability and mechanical properties in CoTiVNi-based superalloys

: Enhanced fuel efficiency and engine performance have driven interest in Co-based superalloys reinforced by coherent γ' dispersed in the matrix with low stacking fault energy (SFE). However, poor microstructure stability due to thermodynamically unstable γ' phases limits their application. A (multi-component diffusion multiple) MCDM approach was employed to efficiently explore composition-microstructure-property relationships of the novel Co-Ti-V-Ni alloys in the present work. Two alloy groups (A: high Ni, B: low Ni) with varying V/Ti ratios were designed, homogenized, and analyzed via EPMA, FE-SEM, in situ XRD, TEM, and mechanical testing. Results revealed that γ' phase stability decreased with increasing Ni, contrasting prior studies where Ni improved γ' stability in Al-containing systems. In situ XRD demonstrated temperature-dependent γ/γ' lattice misfit, with Group A exhibiting higher misfits than Group B, and the lattice misfit decreased with rising V/Ti ratio. Alloy 4# showed anomalous strength increase at 750°C, attributed to dislocation cross-slip. The deformation mechanisms of the alloy exhibit a temperature-dependent evolution: at room temperature, the matrix primarily undergoes deformation through SFs, Lomer-Cottrell locks (LCs), and HCP phase formation. As the temperature increases to 750°C, deformation twins progressively dominate in the matrix. However, upon further heating to 800°C, the deformation behavior reverts to a combination of SFs and LC locks as the primary mechanisms. SFE calculations indicated a high-temperature chemical segregation-assisted SF formation. This work highlights the efficiency of MCDM in alloy design and underscores the prominent roles of V in optimizing Co-based superalloys, providing insights for future development of thermally stable, high-performance materials.