Quantitative determination of strain fields around Ni4Ti3 precipitates in NiTi

High-resolution transmission electron microscopy and image-processing techniques are used to measure the strain fields surrounding coherent Ni4Ti3 precipitates in an austenitic Ni51Ti49 matrix. Images are recorded in the [1 1 1¯]B2 and the [1 0 1¯]B2 zones, and the {1 1  0}B2 interplanar spacings are used to determine the strain induced by both small (50 nm diameter) and large (300 nm diameter) precipitates. From these observations, the maximum strain in the surrounding matrix is mapped and identified as compressive or tensile. Interactions between strain fields of different precipitates are also investigated. A simple model for the observed strain is proposed and compared to the classical Eshelby solution for an ellipsoidal inclusion.