Inter-martensite strain evolution in NiMnGa single crystals

✍ Scribed by R.F. Hamilton; H. Sehitoglu; K. Aslantas; C. Efstathiou; H.J. Maier

• Publisher: Elsevier Science
• Year: 2008
• Tongue: English
• Weight: 534 KB
• Volume: 56
• Category: Article
• ISSN: 1359-6454
• DOI: 10.1016/j.actamat.2008.01.007

✦ Synopsis

Stress-induced martensitic transformations are clarified in classes of NiMnGa alloys which undergo the stress-free, thermal-induced inter-martensite transformation austenite (A) pre-martensite (PM) martensite. This study implements a comprehensive experimental approach, including analysis of the strain-temperature and stress-strain response, which discloses stress-induced inter-martensite transitions. The evolution of the transitions is elucidated using in situ digital image correlation (DIC) measurements of meso-scale strain fields. Under stress, this body of work unequivocally demonstrates that the transformation path becomes A PM I 10M. The Iphase is an intermediate stress-induced martensite with a modulation period between three and five-layers. Owing to the intermediate transition, the thermal hysteresis in the strain-temperature response is tiny (<10 °C) compared with the hysteresis (32 °C) for A 10M. The differential hysteresis levels are rationalized based on a thermo-mechanical formulation. Meso-scale DIC measurements quantify inter-martensite strain levels, which are indistinguishable from macro-scale stress-strain and strain-temperature responses.