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FeMnAlNi alloys have emerged as one of the most promising SMA candidates for large scale structural applications due to their cost-efficiency, excellent superelasticity and low temperature dependence of the critical stress levels with a large superelasticity window.
The superelastic performance of FeMnAlNi is highly dependent on the size of nano-precipitates, the crystallographic orientation of the individual grains and the ratio of relative grain size to the dimension of component. When subjected to loading, FeMnAlNi alloys show a change in metamagnetic response where deformations can be easily detected by the magnetization response of the alloy. From an application point of view, this property can be harnessed as a non-contact strain sensor in the next generation of structural monitoring applications. The fundamental understanding of the microstructure and the ability to increase the component dimension of the alloys for large scale applications is therefore of considerable importance in the development of FeMnAlNi alloys.
In this study, the fundamental mechanisms behind the abnormal grain growth triggered by thermal cycling was studied. A new crystal reorientation mechanism that results in abrupt crystallographic orientation changes in bulk single crystals is reported for the first time.
Then, a new FeMnAlNi SMA cable was developed and showed that favorable wire properties can be scaled into larger assemblies. Finally, FeMnAlNi was developed as a non-contact sensor to monitor stresses and strains in structural systems. It was found that the magnetic characteristics of the alloy changes when the stresses are applied, and a direct correlation was established between the magnetic response and the remnant deformation. The result of this study is a first step towards utilizing novel FeMnAlNi SMAs in next generation structural monitoring where structural and sensing elements are integrated. The findings also open up new possibilities for the development of new large single crystals with tailorable orientations.