Phase Transformation Graph and Transformation Pathway Engineering for Shape Memory Alloys

• DOI: 10.1007/s40830-020-00271-5
• Publication Date: 2020-02-04T20:03:26Z
• Authors: Yipeng Gao; Taiwu Yu; Yunzhi Wang
• Keywords: Thermoelastic damping; Temperature cycling

Even though martensitic transformations (MTs) in shape memory alloys (SMAs) are thermoelastic (i.e., fully reversible) and the polydomain structures of martensite are self-accommodating with invariant-plane strains, dislocations and sometimes grain boundaries seems to be the inevitable byproducts of the transformation during either thermal or stress cycling, similar to what have been observed during MTs in non-SMAs such as steels. These characteristics associated with MT cycling can lead to some serious problems such as dimensional instability and functional fatigue. In this review, we introduce a recently developed theoretical construct called phase transformation graph (PTG) analysis and show that defect generation in SMAs and their functionality and performance are closely related to the topology of their PTGs. Using PTG topology as a guide, we discuss design strategies to alter the topology of PTGs for high-performance SMAs with improved functionality and functional fatigue resistance. Most of our predictions have been confirmed by experimental characterization and testing. The PTG analysis could open a new avenue for judicious design of next-generation SMAs for widespread technological applications.