Journal
ACTA MATERIALIA
Volume 60, Issue 4, Pages 1514-1527Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2011.11.043
Keywords
Coherent precipitate; Elastic interaction; Nucleation; Aging effect; Phase field simulation
Funding
- NASA
- Supersonics Project (Dale Hopkins, API)
- NSF [DMRI008349]
- US Department of Energy, Office of Basic Energy Sciences [DE-SC0001258]
- Direct For Mathematical & Physical Scien
- Division Of Materials Research [1008349] Funding Source: National Science Foundation
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A new precipitate phase named P-phase has recently been identified in (Ni,Pt)Ti high temperature shape memory alloys. In order to understand the roles played by the fine coherent P-phase precipitates in determining the martensitic transformation temperature (M-s), strength of the B2 matrix phase, dimensional stability and shape memory effect of the alloys, a phase field model of P-phase precipitation is developed. Model inputs, including lattice parameters, precipitate matrix orientation relationship, elastic constants and free energy data, are obtained from experimental characterization, ab initio calculations and thermodynamic databases. Through computer simulations, the shape and spatial distribution of the P-phase precipitates, as well as the compositional and stress fields around them, are quantitatively determined. On this basis, the elastic interaction energy between the P-phase precipitates and a martenstic nucleus is calculated. It is found that both the chemical non-uniformity and stress field associated with the P-phase precipitates are in favor of the martensitic transformation. Their relative contributions to the increase in M-s temperature are quantified as a function of aging time and the result seems to agree with the experimental measurements. The shape and spatial distribution of the P-phase precipitates predicted by the simulations also agree well with experimental observations. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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