The Impact of Martensite Deformation on Shape Memory Effect Recovery Strain Evolution

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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 languageEnglish (US)
Pages (from-to)3481-3489
Number of pages9
JournalMetallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Volume46
Issue number8
DOIs
StatePublished - Aug 25 2015

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics
  • Mechanics of Materials
  • Metals and Alloys

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