The following has kindly been provided for teaching purposes by Donimique (Nick) Schryvers and Cao Sanshan of the Electron Microscopy for Materials Science section of the University of Antwerp. Detailed descriptions can be found in in:
The presence of Ni4Ti3 precipitates in the body-centred cubic based B2 matrix of binary Ni-Ti alloys plays an important role in the unique shape memory and superelasticity properties of these and related systems due to their particular influence on the related B2 to B19’ martensitic and R-phase transformations.
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This figure shows the lenticular-shaped Ni4Ti3 precipitates with a central plane parallel to the crystallographic {111} B2 planes of the B2 matrix via conventional bright-field transmission electron microscope observation. There are 8 variants of Ni4Ti3 precipitates in total, but since two variants share the same central plane, only four different orientations are observed in a scanning electron micrograph as is shown in the scheme. |
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This figure shows a 3D reconstruction of a volume of aligned Ni4Ti3 precipitates in a Ni51Ti49 single crystal after 10 h annealing at 550°C under <111> compression of 50 MPa (a), one of the individual precipitates with a close to cylindrical morphology (b), and a lamella with an irregular morphology containing a contiguous precipitate and two individual ones (c). |
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This figure shows 3D reconstructions of the heterogeneous Ni4Ti3 precipitates in the grain interior (a) and near grain boundary (b) regions in a Ni50.8Ti49.2 polycrystal after 1 h annealing at 500°C. Different colors are used to distinguish between different variants of precipitates. The precipitates show a notable decrease in volume and a significant increase in number when moving towards the grain boundary. |
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