Manufacturing of nickel-titanium shape memory alloy and shape memory training

Shape memory alloys (SMA) are successfully used for their potential use as functionalmaterial in many engineering and medical applications. The technological importance ofshape memory alloys is coming from their shape memory effect (SME) and superelastic (SE)capability. SME and SE capability are due to martensitic phase transformation, that istriggered by changing temperature and applied stress.In this study, in order to manufacture nickel-titanium shape memory alloy, commerciallypure Ni and Ti are measured and cast in vacuum arc and vacuum induction furnace, toproduce equiatomic structure. After successful manufacturing, DSC and microscopicalanalysis was applied to alloys NiTi 12-3, NiTi 7-3, NiTi 4-3 and NiTi 3-2 for materialcharacterization, to determine their transformation temperature and phase structure.Additionally, Vickers hardness and X-Ray diffraction phase analysis were performed and theshape memory capabilities of the alloys were studied with shape memory trainingexperiments.Among the produced nickel-titanium alloys, the one with highest shape memory capability isdetermined to be the one cast in zirconia crucible in three remelting castings, in4mm.x4mm.x65mm dimensions, namely NiTi 12-3. EDS analysis showed the atomicpercentage to be 50.10 % Ti and 49.90 % Ni. DSC analysis was done to find out the phasetransformation temperatures.Among the heat treatment that were applied to the produced alloys, the one resulting thehighest shape memory ability is found to be, holding at 550ºC for 10 minutes in mould andthan quenching in water. During shape memory training experiments, if the alloy, that hasundergone permanent deformation in martensitic phase, is prevented from returning to theoriginal shape during heating, it has been observed that the shape memory recovery of thealloy diminishes significantly. Shape memory training experiments revealed that the producedNiTi 12-3 alloy loses all of its shape memory, if it is prevented from returning to the previousshape at temperatures above 500ºC.Keywords: Shape memory alloys, Ni-Ti alloy, Shape memory trainingJURY:1. Assoc.Prof.Dr. Nurhan CANSEVER (Supervisor) Date : 14 .12.20052. Prof. Dr. Adnan DİKİCİOĞLU Page: 1283. Prof..Dr. Mustafa ÇİĞDEM4. Prof.Dr. Adem BAKKALOĞLU5. Assist.Prof.Dr. Levent TRABZON