Constrained hierarchical twinning in Ru-based high temperature shape memory alloys

• Published in: Acta materialia 2016-06, Vol.111, p.283-296
• Main Authors: Manzoni, Anna M., Denquin, Anne, Vermaut, Philippe, Prima, Frédéric, Puente-Orench, Inés, Pauly, Christoph, Mücklich, Frank, Portier, Richard A.
• Format: Article
• Language: English
• Subjects: Alloys; Constraints; EBSD; Engineering Sciences; Laminates; Martensitic transformations; Materials; Microstructure; Ru–Ta; Shape memory alloys; Transformations; Transmission electron microscopy; Twinning
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2016.03.067

The microstructure of high temperature shape memory alloys of the Ru-Ta and Ru-Nb family are investigated in detail. After cooling from the high temperature cubic β phase the off-stoichiometric alloys show a compound twinning in the tetragonal β′ phase which prevails at room temperature and can be observed as two levels of laminates A and C [1]. The stoichiometric alloys are characterized by a second phase transformation from β′ to monoclinic β″, which adds another type of twinning. The latter belongs to the monoclinic P2/m structure and has been created out of one of the lost symmetry elements from the tetragonal P4/mmm phase during the β′ → β″ transformation. The unusual characteristic of this new twinning, called B, is the fact that it has an intermediate size between the A and C twins that belong to the high-temperature transformation β′ → β″. This is due to a second constrained martensitic transformation. [Display omitted]