High-temperature shape memory alloys based on the RuNb system

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 481; pp. 702 - 706
• Main Authors: Chastaing, K., Denquin, A., Portier, R., Vermaut, P.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 25.05.2008
• Subjects: High-temperature shape memory alloys; Microstructure; Shape memory effect; Microstructure; High-temperature shape memory alloys; Shape memory effect
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2006.10.217

Many applications of shape memory alloys (SMAs) require the development of alloys with high martensitic transformation (MT) temperatures. Among the different systems for high temperature SMAs, equiatomic RuNb alloys demonstrate both shape memory effect (SME) and MT temperatures above 800 °C. This work investigates Ru 50− x Nb 50+ x (at.%) alloys and shows that Nb content significantly affects the MT behavior. Alloys near the equiatomic composition ( x = 0, 2, 4) undergo two displacive transformations on cooling: β (B2) → β′ (body centered tetragonal) → β′′ (monoclinic). The Ru 45Nb 55 alloy exhibits a single transition from cubic to tetragonal on cooling. This MT gives rise to a highly twinned microstructure with a (0 1 1) compound-twinning mode and is considered to be responsible for the SME in both types of alloys. The reorientation of martensite variants during deformation has been confirmed through scanning electron microscopy of compression specimens. A promising shape memory behavior is obtained through three-point bend tests performed both in the β′ and β′′ phases.