Solubility and ordering of Ti,Ta, Mo and W on the Al sublattice in L12-Co3Al |
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| Affiliation: | 1. Interdisciplinary Centre for Advanced Materials Simulation, Ruhr-Universität Bochum, Bochum, Germany;2. Max-Planck-Institute for Iron Research, Düsseldorf, Germany;3. Institute of Advanced Ceramics, Hamburg University of Technology, Hamburg, Germany;1. Department of Materials Science & Engineering, North Carolina State University, Raleigh, NC 27695-7907, United States;2. Department of Materials Design and Innovation, University at Buffalo – the State University of New York, Buffalo, NY 14260-5030, United States;1. Department of Materials Science and Engineering, College of Materials and Fujian Provincial Key Laboratory of Materials Genome, Xiamen University, Xiamen, 361005, PR China;2. Department of Materials Science, Graduate School of Engineering, Tohoku University, Sendai, 980-8579, Japan;1. Department of Materials Engineering, Indian Institute of Science, Bangalore, 560012, India;2. Department of Microstructure Physics and Alloy Design, Max-Planck-Institute für Eisenforschung, 40237, Düsseldorf, Germany;3. Materials Research Center, Indian Institute of Science, Bangalore, 560012, India |
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| Abstract: | Co–Al–W-based alloys are promising new materials for high-temperature applications. They owe their high-temperature strength to hardening by ternary L12-Co3(Al1−xWx) precipitates, which may form even though binary Co3Al is not stable. In the current work, density functional theory calculations are performed to study the solubility and ordering of the transition metals W, Mo, Ti, and Ta at the Al sublattice in L12-Co3Al. The sublattice disorder is modelled with a newly parametrised cluster expansion and compared to results using special quasi-random structures. Our results for W and Mo show that the mixing energy exhibits a minimum at approximately x = 0.7. However, the computed small values of the mixing energies indicate that W and Mo atoms are fully disordered with the Al atoms already at low temperatures. For Ti and Ta we find no sizeable driving force for ordering with the Al atoms. The computed solubilities on the Al sublattice obtained are in the range of 40–80 meV/atom for W and Mo and less than 25 meV/atom for Ti and Ta. |
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| Keywords: | A. Functional alloys A. Intermetallics B. Phase stability D. Site occupancy E. ab-initio calculations E. Ordering energies |
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