Martensite crystal structure in Ru-based high temperature shape memory alloys

• Published in: Materials characterization Vol. 142; pp. 109 - 114
• Main Authors: Manzoni, A.M., Wallez, G., Denquin, A., Prima, F., Portier, R.A., Vermaut, P.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.08.2018; Elsevier
• Subjects: ATOMIC DISPLACEMENTS; Chemical Sciences; Engineering Sciences; INTERFACES; MARTENSITE; MATERIALS SCIENCE; MICROSTRUCTURE; MONOCLINIC LATTICES; PHASE TRANSFORMATIONS; Physics; RUTHENIUM ALLOYS; SHAPE MEMORY EFFECT; SPACE GROUPS; TRANSMISSION ELECTRON MICROSCOPY; X-RAY DIFFRACTION; ALLOY; MARTENSITE; ALLLIAGE
• ISSN: 1044-5803; 1873-4189
• DOI: 10.1016/j.matchar.2018.05.019

High temperature shape memory alloys RuNb and RuTa were investigated by X-ray diffraction in order to determine the structure of the low temperature β” martensite. Powder X-ray diffraction and Rietveld analysis confirm the monoclinic symmetry and allow a precise determination of the atom positions. The low temperature microstructure is the result of a martensitic transformation from a tetragonal β′ martensite. The analysis of how it is controlled by the space groups of the two phases and by their relative orientation is performed by transmission electron microscopy. A three level twinned microstructure is recognized in the β” phase. The investigation at the smallest scale twins reveals the presence of wavy contrast boundaries which are typical for translation interfaces. High resolution transmission electron microscopy images, accompanied by phase contrast imaging analysis, have been used to determine the translation vectors associated to the interfaces. These displacements are the translations of the tetragonal β′ phase which are lost during the transformation. The combination of X-ray diffraction and transmission electron microscopy investigation allows the suggestion of a global distortion mechanism that explains the atomic displacements in the β” form. •A three level twinned microstructure is recognized in the β″ phase.•Wavy contrast boundaries which are typical for translation interfaces•Displacements are translations of tetragonal β′ phase, lost during transformation.•Six times bigger monoclinic cell is characterized by the disappearance of 5 translations.