Effects of alloying elements on thermal expansions of γ-Ni and γ′-Ni ₃Al by first-principles calculations

The effects of alloying elements (Al, Cr, Hf, Pt, Y, and Zr) on the coefficients of thermal expansion (CTE) of face-centered-cubic Ni (γ) and L1 ₂-Ni ₃Al (γ′) phases have been investigated in terms of the first-principles quasi-harmonic approach by considering both the vibrational and thermal electronic contributions. By combining the present CTE data and the compositions and phase fractions of γ and γ′, the CTE for some Ni-Al-base alloys are predicted and compared with available experimental measurements in the literature, showing good agreement. It is observed that the addition of Pt is effective in reducing the CTE of both γ and γ′ phases, resulting in lower expansion mismatch between the bond coat and the thermally grown oxide alumina layer, as shown by the predicted CTE of Ni-22 Al-x Pt (at.%) alloys (x = 5, 10, 15, 20, 25, 30).