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In-situ TEM stress induced martensitic transformation in Ni50.8Ti49.2 microwires

Journal Contribution - Journal Article

Abstract In-situ transmission electron microscopy tensile straining is used to study the stress induced martensitic transformation in Ni50.8Ti49.2. Two microwire samples with different heat treatment are investigated from which one sin gle crystal and three polycrystalline TEM specimens, the latter with micro- and nano-size grains, have been produced. The measured Young’s modulus for all TEM specimens is around 70 GPa, considerably higher than the averaged 55 GPa of the original microwire sample. The height of the superelastic stress plateau shows an inverse relationship with the specimen thickness for the polycrystalline specimens. Martensite starts nucleating within the elastic region of the stress–strain curve and on the edges of the specimens while also grain boundaries act as nucleation sites in the polycrystalline specimens. When a martensite plate reaches a grain boundary in the polycrys talline specimen, it initiates the transformation in the neigh boring grain at the other side of the grain boundary. In later stages martensite plates coalesce at higher loads in the stress plateau. In highly strained specimens, residual martensite remains after release.
Journal: Shape Memory and Superelasticity
ISSN: 2199-384X
Issue: 2
Volume: 5
Pages: 154 - 162
Publication year:2019
Accessibility:Open