Composition and temperature dependence of twinning stress in non-modulated martensite of Ni-Mn-Ga-Co-Cu magnetic shape memory alloys

• Published in: Scripta materialia Vol. 144; pp. 52 - 55
• Main Authors: Soroka, A., Sozinov, A., Lanska, N., Rameš, M., Straka, L., Ullakko, K.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.02.2018
• Subjects: Ferromagnetic shape memory alloy; Heusler phases; Magnetic shape memory; Martensite; Twinning; Magnetic shape memory; Ferromagnetic shape memory alloy; Twinning; Heusler phases; Martensite
• ISSN: 1359-6462; 1872-8456
• DOI: 10.1016/j.scriptamat.2017.09.046

We study compositional and thermal dependences of lattice parameters and twinning stress σTW in Ni50-xMn25-yGa25-zCoxCuy+z magnetic shape memory alloys with non-modulated tetragonal crystal structure. The σTW was found to decrease with increasing temperature with a slope from −0.0076 to −0.0181MPa/K. The σTW=0.47–0.81MPa values measured near composition-specific austenite transformation temperatures TA were discovered to depend linearly on the c/a ratio with a slope of 14MPa. We predict that the further decrease of c/a ratio to the level of 1.085–1.104 can result in extremely low σTW≈0.1MPa in non-modulated martensite. [Display omitted]