12 July 1999 Dilatometric and electrical resistivity measurements in various phases of Nitinol
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Transformation characteristics of near equiatomic, prior cold worked Nitinol have been studied through thermomechanical analysis and electrical resistivity measurements, using TMA-50 and a four-probe setup, respectively. The dilatometric and electrical resistivity curves are obtained for the samples heat-treated between 300 and 600 degrees C. Examination of the dilation curves show that, in the martensitic phase there is positive thermal expansion where as, during M yields A transformation there is also uniaxial contraction till Af. In the austenitic phase there is positive thermal expansion and these thermal expansion values agree with the published values for respective phases. While cooling, at Ms uniaxial expansion starts and this continues till Mf is reached. In the present work the R-phase and associated hysteresis has also been investigated. On cooling from A-phase, uniaxial expansion is found to start from Rs and it stops at Rf. The transformation temperatures determined in this method agree very closely with those values obtained using electrical resistivity probe. Hysteresis area is found to be smaller in the A $ARLR M transformation. The area under hysteresis loop associated with R-phase is found to be a constant against thermal cycling. Certain applications like clamps and splints require a large hysteresis loop, while some solid sate actuators require relatively smaller hysteresis loops. An attempt is made to explain R-phase transformation in terms of thermo-mechanical data.
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Jayagopal Uchil, Jayagopal Uchil, Kotekar Panduranga Mohanchandra, Kotekar Panduranga Mohanchandra, K.K. Mahesh, K.K. Mahesh, Kumara K. Ganesh, Kumara K. Ganesh, } "Dilatometric and electrical resistivity measurements in various phases of Nitinol", Proc. SPIE 3675, Smart Structures and Materials 1999: Smart Materials Technologies, (12 July 1999); doi: 10.1117/12.352804; https://doi.org/10.1117/12.352804

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