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Linking a completely three-dimensional nanostrain to a structural transformation eigenstrain
Wim Tirry1, Dominique Schryvers
1EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020, Antwerp, Belgium. wim.tirry@ua.ac.be
Nature Materials
|June 23, 2009
Summary
Nickel-Titanium (Ni-Ti) shape-memory alloys exhibit an R-phase transformation due to Ni(4)Ti(3) precipitates. This study reveals the R-phase may compensate for precipitate-induced elastic strain.
Area of Science:
- Materials Science
- Metallurgy
- Solid-State Physics
Background:
- Nickel-Titanium (Ni-Ti) is a widely used shape-memory alloy.
- Commercial Ni-Ti alloys contain Ni(4)Ti(3) precipitates after thermal treatment.
- These precipitates can induce an intermediate R-phase transformation.
Purpose of the Study:
- To investigate the origin of the R-phase transformation in Ni-Ti alloys.
- To measure the elastic strain field around Ni(4)Ti(3) precipitates.
- To determine if the R-phase compensates for precipitate-induced strain.
Main Methods:
- Utilized atomic-resolution transmission electron microscopy (ARTEM).
- Employed geometrical phase analysis (GPA) to quantify strain fields.
- Combined 2D measurements from two crystallographic directions to reconstruct the 3D strain matrix.
Main Results:
- Successfully measured the elastic strain field surrounding Ni(4)Ti(3) precipitates.
- Determined the three-dimensional strain matrix from experimental data.
- Found a strong similarity between the measured strain matrix and the R-phase eigenstrain.
Conclusions:
- The R-phase transformation is likely initiated by the elastic strain field from Ni(4)Ti(3) precipitates.
- The R-phase formation appears to effectively compensate for the matrix-precipitate lattice mismatch.
- This finding provides insight into the mechanism of intermediate transformations in shape-memory alloys.
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