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

形状记忆合金具有广泛的潜在应用，从支架到飞机发动机的部件，因为它们能够恢复加热时的异常大的应力。这是通过利用母体B2结构和单斜马氏体之间的无扩散转变而发生的，导致了加热和冷却的滞后行为。然而，由于缺乏对大量成分和加工变量如何影响合金性能的了解，目前微调这一行为的能力是有限的。特别令人感兴趣的是滞后宽度，这对这些材料在储存和使用期间的长期稳定性至关重要。因此，本PHD将重点研究不同的合金化添加和工艺条件对NiTi基形状记忆合金性能的影响，包括它们对磁滞宽度的影响。每种合金都将用扫描电子显微镜、电子显微镜和X射线衍射仪进行表征，并用差示扫描量热法测量磁滞宽度。还可以进行拉伸测试，以分析合金的机械性能，以便充分了解成分和加工对其整体性能的影响。

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.