Abstract
Many technological applications are based on functional materials that exhibit reversible first-order ferroelastic transitions, including elastocaloric refrigeration, energy harvesting, and sensing and actuation. During these phase changes inhomogeneous microstructures are formed which fit together different crystalline phases, and evolve abruptly through strain bursts related to domain nucleation and the propagation of phase fronts, accompanied by acoustic emission. Mechanical performance is strongly affected by such microstructure formation and evolution, yet visualisation of these processes remains challenging. Here we report a detailed study of the bursty dynamics during a reversible stress-induced martensitic transformation in a CuZnAl shape-memory alloy. We combine full-field strain-burst detection, performed by means of an optical grid method, with the acoustic tracking of martensitic strain avalanches using two transducers, which allows for the location of the acoustic-emission events to be determined and the measurement of their energies. The matching of these two techniques reveals interface formation, advancement, jamming and arrest at pinning points within the transforming crystal.
Highlights
Many technological applications are based on functional materials that exhibit reversible firstorder ferroelastic transitions, including elastocaloric refrigeration, energy harvesting, and sensing and actuation
They occur via cooperative atomic motions producing rapid changes of lattice structure, and typically form inhomogeneous microstructures involving different coexisting crystalline phases and variants
To shed light on the details of these phenomena, we have studied the strain-avalanching in the stress-induced martensitic transformation in a CuZnAl shape-memory alloy[12,14]
Summary
Many technological applications are based on functional materials that exhibit reversible firstorder ferroelastic transitions, including elastocaloric refrigeration, energy harvesting, and sensing and actuation. They occur via cooperative atomic motions producing rapid changes of lattice structure, and typically form inhomogeneous microstructures involving different coexisting crystalline phases and variants Many technological applications, such as environmentally-friendly elastocaloric refrigeration,[4,5,6] wasteenergy harvesting[7,8], smart sensing and actuating[1,3], are based on functional ferroelastic[2] materials, like shape-memory alloys, exhibiting highly reversible martensites[7,9,10,11].
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