An investigation into the effect of composition and processing on the hysteresis width of NiTi shape memory alloys

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Shape memory alloys have a vast array of potential applications, from stents to components in aircraft engines, due to their ability to recover exceptionally large strains on heating. This occurs by exploiting a diffusionless transformation between a parent B2 structure and monoclinic martensite, giving rise to hysteretic behaviour on heating and cooling. However, the ability to fine tune this behaviour is currently limited, due to a lack of understanding about how the large number of compositional and processing variables impact alloy properties. Of particular interest is the hysteresis width, which is critical for the long-term stability of these materials both during storage and in use. As such, this PhD will focus on the effect of different alloying additions, and processing conditions on the properties of NiTi based shape memory alloys, including their effect on hysteresis width. Each alloy will be characterised using a combination of SEM, TEM and XRD and the hysteresis width measured using DSC. There is also scope to perform tensile testing to analyse the mechanical properties of the alloys, in order to fully understand the effects of composition and processing on their overall behaviour.