Atomic-scale understanding of the effects of Cr and Ti on γ′ growth kinetics in the Ni–Al-X ternary system: Diffusion couple technique and DFT study

Cr and Ti are essential elements in Ni-based superalloys for γ solid solution strengthening and γ′ precipitation strengthening, respectively, enhancing high-temperature performance. Despite the known benefits of high concentrations, the effects of lower Cr and Ti concentrations on γ′ precipitation kinetics remain unclear. This study investigates the temporal evolution of γ′ phase in Ni–Al-X (X = Cr, Ti) system, utilizing diffusion-couple alongside aberration-corrected transmission electron microscopy to unveil atomic-scale effects. Experimental results demonstrate that Cr and Ti accelerate γ′ phase formation due to competition between lattice misfit and interdiffusion. Moreover, γ′ phase forms through an order-disorder transition, regulated by alloy type. First-principles calculations indicate that Cr and Ti favor γ′ phase formation thermodynamically and kinetically. Al compressibility from Cr and Ti doping promotes γ′ formation. These insights aid in designing Ni-based superalloys with improved microstructural stability and high-temperature performance.