| Summary: | 碩士 === 逢甲大學 === 材料科學學系 === 89 === Abstract
The Ti50-x/2Ni40-x/2Cu10Crx alloys( x＝0、0.2、0.6、1.0) were used and prepared by vacuum arc melting technique. We studied the basic properties and superelasticity of these alloys subjected to solution treatment and cold working.
Experiment results reveal that Ti50-x/2Ni40-x/2Cu10Crx alloys exhibit a B2«B19«B19’ two-stage martensitic transformation after solution treatment. The transformation temperature M* decrease，and hardness and shape recovery increase，with increasing Cr content. XRD results show that three phases(B2、B19、B19’)coexist in the Ti50-x/2Ni40-x/2Cu10Crx alloys at room temperature. With increasing of Cr content , the intensity of B2 phase diffraction peak increases. After cold working，DSC results reveal that the transformation temperature decreases. The transformation peaks are broaden and the peak of the B19«B19’ transformation disappears. XRD results reveal that SIP and SIM phenomenon appear during cold working but these phenomena will disappear after a reverse martensitic transformation. In addition , hardness and shape recovery also increase because a lot of dislocations have been created after cold working treatment.
The results of superelasticity test show that Ti50-x/2Ni40-x/2Cu10Crx alloys will exhibit stable superelasticity curves. With increasing of test temperature，the plateau stress(sSIM) increases. However, with increasing the deformation cycles , the plateau stress and the stress hysteresis decrease. After cold working, the stress hysteresis increases because dislocations will prohibit the SIM®P transformation resulting in the decrease of sSIM®P. Meanwhile, the plateau stress decrease because some SIM embryos created during cold working.
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