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Highly mobile twinned interface in 10 M modulated Ni–Mn–Ga martensite / L. Straka in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7450–7463 Titre : Highly mobile twinned interface in 10 M modulated Ni–Mn–Ga martensite : Analysis beyond the tetragonal approximation of lattice Type de document : texte imprimé Auteurs : L. Straka, Auteur ; O. Heczko, Auteur ; H. Seiner, Auteur Année de publication : 2012 Article en page(s) : pp. 7450–7463 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Microstructure  Twinning  X-ray  diffraction  Heusler  phases  Magnetic  shape  memory Résumé : The huge strains that Ni–Mn–Ga magnetic shape memory alloys can achieve are usually described in a tetragonal unit cell approximation of a five-layered modulated (10 M) crystal structure. Here we analyze the impact of a slight orthorhombic and monoclinic distortion of the 10 M structure in Ni50.2Mn28.3Ga21.5at.% single crystal. Combining dedicated experiments to probe the microstructure, structure and mechanical properties with calculation using elastic continuum theory, we prove the existence of fine a/b-laminates within modulation macrotwins of the order of 100 micrometers in size. This complex twin microstructure containing a Type II macrotwin interface is associated with an extraordinarily low twinning stress of between 0.05 and 0.3 MPa, while Type I twins exhibit twinning stress of about 1 MPa. The findings provide important guidelines for designing the martensitic microstructure for more efficient actuators. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006574 [article] Highly mobile twinned interface in 10 M modulated Ni–Mn–Ga martensite : Analysis beyond the tetragonal approximation of lattice [texte imprimé] / L. Straka, Auteur ; O. Heczko, Auteur ; H. Seiner, Auteur . - 2012 . - pp. 7450–7463. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7450–7463 Mots-clés : Microstructure  Twinning  X-ray  diffraction  Heusler  phases  Magnetic  shape  memory Résumé : The huge strains that Ni–Mn–Ga magnetic shape memory alloys can achieve are usually described in a tetragonal unit cell approximation of a five-layered modulated (10 M) crystal structure. Here we analyze the impact of a slight orthorhombic and monoclinic distortion of the 10 M structure in Ni50.2Mn28.3Ga21.5at.% single crystal. Combining dedicated experiments to probe the microstructure, structure and mechanical properties with calculation using elastic continuum theory, we prove the existence of fine a/b-laminates within modulation macrotwins of the order of 100 micrometers in size. This complex twin microstructure containing a Type II macrotwin interface is associated with an extraordinarily low twinning stress of between 0.05 and 0.3 MPa, while Type I twins exhibit twinning stress of about 1 MPa. The findings provide important guidelines for designing the martensitic microstructure for more efficient actuators. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006574