Abstract
The one-way shape memory effect of polycrystalline NiTi is investigated after differential levels of martensite deformation. Martensite naturally forms an energy-minimizing configuration, referred to as self-accommodated, of differently oriented martensite variants, which are internally twinned. Stress preferentially orients a select variant that eventually detwins and plastically deforms at the highest stress levels. In this work, the underlying morphology is ascertained based on the evolution of micro-scale deformation measurements using digital image correlation analysis of three characteristic material responses. An initial martensitic structure is deformed at constant temperature. The forward austenite-to-martensite and reverse martensite-to-austenite phase transformations take place during temperature cycling under a constant stress. The austenite-to-martensite transformation is tensile stress induced at a constant temperature and initiates via a localized strain band. For the conversion of self-accommodated martensite to orientated morphology and further deformation, spatially heterogeneous strains accrue over the entire specimen surface. Shape memory recovery during heating, on the other hand, culminates with a centralized strain localization that persists as recovery approaches completion. The recovery temperature differential (Af − As) depends on the extent of deformation. This work characterizes the influence of stress on phase transformation and martensite deformation morphology for deformation in the martensitic state compared to the stress-induced phase transformation.
Original language | English (US) |
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Pages (from-to) | 3481-3489 |
Number of pages | 9 |
Journal | Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science |
Volume | 46 |
Issue number | 8 |
DOIs | |
State | Published - Aug 25 2015 |
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Mechanics of Materials
- Metals and Alloys