Benedek, R. and van de Walle, A. and Gerstl, S. S. A. and Asta, M. and Seidman, D. N. and Woodward, C. (2005) Partitioning of solutes in multiphase Ti–Al alloys. Physical Review B, 71 (9). Art. No. 094201. ISSN 1098-0121. http://resolver.caltech.edu/CaltechAUTHORS:BENprb05
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First-principles calculations based on a plane-wave pseudopotential method, as implemented in the VASP code, are presented for the formation energies of several transition-metal and non-transition-metal dopants in Ti–Al alloys. Substitution for either Ti or Al in gamma-TiAl, alpha2-Ti3Al, Ti2AlC, and Ti3AlC are considered. Calculated (zero-temperature) defect formation energies exhibit clear trends as a function of the periodic-table column of transition metal solutes. Early transition metals in TiAl prefer the Ti sublattice, but this preference gradually shifts to the Al sublattice for late transition metals; the Ti sublattice is preferred by all transition metal solutes in Ti3Al. Partitioning of solutes to Ti3Al is predicted for mid-period transition elements, and to TiAl for early and late transition elements. A simple Ising model treatment demonstrates the plausibility of these trends, which are in excellent overall agreement with experiment. The influence of temperature on formation energies is examined with a cluster expansion for the binary TiAl alloys and a low temperature expansion for dilute ternary alloys. Results for Nb-doped alloys provide insight into the relative sensitivity of solute partitioning to individual contributions to the free energy. Whereas the calculated formation energy of Nb (substitution) at zero temperature favors partitioning to alpha2-Ti3Al, temperature-dependent contributions to the formation free energy, evaluated at 1075 K, favor partitioning to gamma-TiAl, in agreement with experiment.
|Additional Information:||©2005 The American Physical Society. (Received 9 September 2004; revised 1 December 2004; published 4 March 2005) Research at Northwestern University was supported by U.S. Department of Energy Grant Nos. DE-FG02-96ER45597 (RB, SG and DNS) and DE-FG02-01ER45910 (AVDW and MA). CW was supported by the Air Force Office of Scientific Research at the U.S. Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright Patterson AFB under Contract No. F33615-96-C-5258. A grant of computer time at the National Energy Research Computer Center at Lawrence Berkeley Laboratory is gratefully acknowledged. This work was also supported in part by a grant of computer time from the DoD High Performance Computing Modernization Program, at the Aeronautical Systems Center-Major Shared Resource Center, on the IBM-SP3. This project benefited from computing resources provided by the National Partnership for Advanced Computational Infrastructure at the University of Michigan.|
|Subject Keywords:||titanium alloys; aluminium alloys; ab initio calculations; pseudopotential methods; heat of formation; doping; crystal defects; Ising model; segregation|
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|Deposited On:||02 Feb 2007|
|Last Modified:||26 Dec 2012 09:31|
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