Design of High Temperature Shape Memory Alloys

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There is a recent, significant interest in high temperature shape memory alloy capabilities that will broaden the utilization of these materials. Shape memory alloys are unique in their ability to return to their original shape after deformation. The research emphasis of this proposal is on the development of new high temperature shape memory alloys with capabilities above 400 degree Celsius. The crystallography and the atomic displacements leading to the creation of twins, a rearrangement of the atoms, will be investigated via meso-scale modeling. The compositions will be optimized to control the strengths of secondary phases within the material and hence the reversibility of the phase transformations which dictate the material behavior. The research will also hone in on the processing of these materials for sample preparation, including polycrystals and single crystals. The investigation will include experiments to measure the behavior during loading and unloading and heating and cooling under stress in order to develop high temperature resistance for several potential compositions of nickel, titanium, cobalt and iron based shape memory materials with ternary additions. The proposed measurements of local displacements and strains will provide a critical check on the atomic deformation planes and the predicted stress at the onset of twinning in these materials. These measurements will be made with digital image correlation techniques, which will also be advanced during this research. The expected benefit of the research is to establish multi-component shape memory alloys that can operate at higher temperatures with actuation capabilities that can benefit the aerospace and other high temperature industries. The aim is to develop high temperature alloys with shape memory functionality without compromising strength, ductility and durability. The scientific benefits of the research include a better understanding of the mechanical response based on the underlying composition, crystallography, and microstructure. The educational benefits of the research will be enhanced with the preparation of a monograph on shape memory and a series of lectures that combine atomistic calculations with mesoscopic theories. This will be an advancement in the pedagogical treatment of shape memory alloys elevating the materials science and continuum mechanics perspectives and understanding.