Abstract
The effect of Ti and Hf impurities on the $(111)$ antiphase boundary (APB) energy of ${\mathrm{Ni}}_{3}\mathrm{Al}$ is investigated via ab initio calculations. Cluster expansion is performed to predict supercell total energies sampled in a Monte Carlo approach that accounts for nondilute point defects at finite temperature, obtaining APB energies as a function of impurity concentration and temperature. Of the two ternary elements, Hf is more effective in increasing the APB energy. While the $(111)$ APB energy of a pure ${\mathrm{L}1}_{2}$ material requires at least second-nearest-neighbor interactions, we observe a strong correlation between impurity-induced APB energy enhancement and formation of first-nearest-neighbor Ni-Ni bonds across the APB due to symmetry breaking. Using a linear-chain model and effective bond energies derived from effective cluster interactions, we propose a mechanism that explains why Hf is more effective than Ti.
Highlights
Ni3Al is a technologically important material that is used for γ precipitate strengthening in Ni-based superalloys
To obtain antiphase boundary (APB) energy as a function of temperature and impurity concentration, we have developed a cluster expansion (CE) method based on density functional theory (DFT) total-energy calculations and
For both Ni3Al:Ti and Ni3Al:Hf systems, strong correlation is observed between APB energy enhancement and formation of Ni3Al interfacial β11 (Ni-Ni) first-nearest-neighbor bonds
Summary
Ni3Al is a technologically important material that is used for γ precipitate strengthening in Ni-based superalloys. Further enhancement in strength can be achieved by solute additions, which has been extensively studied in experiments [1]. In precipitates such as γ significant strengthening occurs when an ordinary ( [110]). Dislocation cuts the precipitate producing an antiphase boundary (APB). The resistance to shear is proportional to the APB energy, which is sensitive to composition and temperature. The Ni-Al γ -γ phase boundary is fairly insensitive to temperature and binary composition, so the ratio of Ni to Al in Ni3Al is fairly constant over a range of alloy compositions. The effect of off-stoichiometry [4] and that of transition-metal additions [5,6] on the APB energy of Ni3Al have been investigated from computational approaches
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