Material Characterization of Manufactured NiTi SMAs

Shape memory alloys (SMAs) are successfully used for their great potential use as functional materials in many engineering and medical applications. The technological importance of shape memory alloys is coming from their shape memory effect (SME) and superelastic (SE) capability. SME and SE capability are due to martensitic transformation (MT), that is triggered by changing temperature and applied stress resulting in a transformation of the crystal structure from austenite parent phase to martensite phase.
In this study, commercially pure nickel and titanium are cast in vacuum arc and vacuum induction furnace, to produce equiatomic structure. After successful manufacturing, DSC and microscopically analysis was applied to alloys NiTi 12-3, NiTi 7-3, NiTi 4-3 and NiTi 3-2 for material characterization, to determine their transformation temperature and phase structure. Additionally, Vickers hardness and X-Ray diffraction phase analysis were performed and the shape memory capabilities of the alloys were studied with shape memory training experiments.
Among the produced nickel-titanium alloys, the one with highest shape memory capability is determined to be the one cast in zirconia crucible in three remelting castings, in 4mm.x4mm.x65mm dimensions, namely NiTi 12-3. EDS analysis showed the atomic percentage to be 50.10 % Ti and 49.90 % Ni. DSC analysis was done to find out the phase transformation temperatures.The optical micrograph observations have been carried out to illustrate
the variation of the microstructures in the same heating/cooling rate for each samples. The effects of annealing on the transformation behavior of
NiTi 12-3 shape memory alloy have been extensively studied and well characterized.