[MRO] Oligocrystalline Shape Memory Alloys

• Main Authors: Chen, Ying (Contributor), Schuh, Christopher A. (Contributor), Ueland, Stian Melhus (Contributor)
• Other Authors: Massachusetts Institute of Technology. Department of Materials Science and Engineering (Contributor)
• Format: Article
• Language: English
• Published: Wiley Blackwell, 2013-08-26T21:04:25Z.
• Subjects: Article
• Online Access: Get fulltext

 Copper-based shape memory alloys (SMAs) exhibit excellent shape memory properties in single crystalline form. However, when they are polycrystalline, their shape memory properties are severely compromised by brittle fracture arising from transformation strain incompatibility at grain boundaries and triple junctions. Oligocrystalline shape memory alloys (oSMAs) are microstructurally designed SMA structures in which the total surface area exceeds the total grain boundary area, and triple junctions can even be completely absent. Here it is shown how an oligocrystalline structure provides a means of achieving single crystal-like SMA properties without being limited by constraints of single crystal processing. Additionally, the formation of oSMAs typically involves the reduction of the size scale of specimens, and sample size effects begin to emerge. Recent findings on a size effect on the martensitic transformation in oSMAs are compared and a new regime of heat transfer associated with the transformation heat evolution in these alloys is discussed. New results on unassisted two-way shape memory and the effect of loading rate in oSMAs are also reported.