Shape Memory Alloys via Halide-Activated Pack Equilibration
Fabrication of shape memory alloy (SMA) components based on NiTi is challenging due to the precision with which elemental composition and microstructure must be controlled during processing to achieve desired shape memory behavior. Herein, a method to control chemistry in an NiTi SMA via halide-activated pack equilibration (SHAPE) against a constant chemical potential reservoir is described. To demonstrate the efficacy of the SHAPE process, an initially titanium-deficient specimen (pure nickel foam) has been equilibrated against an excess of an intimately mixed two-phase pack (NiTi + Ti2Ni) in the presence of a vapor phase transport agent (iodine). The two-phase pack regulates chemical potentials in this two-component system in accordance with Gibbs' phase rule. Ti-rich NiTi foams thus produced exhibit reproducible and well-defined phase transformation behaviors. The SHAPE process is advantageous for the fabrication of shape memory components of varying areal dimension, shape, and/or complexity owing to independence of the equilibrium state of the system from either the initial state of the specimen or the details of the process kinetics. Current limitations and prospects for the application of this method to improve the quality of SMA components are briefly discussed.
A. S. King et al., "Shape Memory Alloys via Halide-Activated Pack Equilibration," Advanced Engineering Materials, Wiley, Feb 2022.
The definitive version is available at https://doi.org/10.1002/adem.202101494
Materials Science and Engineering
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Keywords and Phrases
Chemical Vapor Transport; NiTi; Reaction Processing; Shape Memory Alloy
International Standard Serial Number (ISSN)
Article - Journal
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03 Feb 2022