EFFECT OF SOAKING TIME ON THE THERMOMECHANICAL RESPONSE OF SINTERED NITI SHAPE MEMORY ALLOY

Out of all the several metal systems that can exhibit shape memory behavior, nickel-titanium (NiTi or nitinol) is still the most commonly used. An effective method for manufacturing nitinol components is by the process of sintering, which entails compressing elemental or pre-alloyed metal powder and using a suitable mold. Recent studies show that pressureless sintering of uncompacted pre-alloyed powder is a feasible method for fabricating nitinol. Using this technique omits the need to compress the powder into a green part prior to sintering. This study investigates the impact of soaking time on the production of nitinol by pressureless sintering of pre-alloyed NiTi shape memory alloy powder. The process entails heating and compacting nitinol at a specific rate and duration in a vacuum to facilitate its sintering. The material's shape memory capability is evident from the phase transition peaks observed in the differential scanning calorimetry (DSC) thermograms obtained. It is shown that as the soaking time increases, the peak intensity decreases because of Ni rich area formation of Ni3Ti. In addition, energy dispersive spectroscopy (EDS) is conducted using scanning electron microscopy (SEM) to show that the phases present in the samples are mainly NiTi and Ni3Ti. Vickers hardness test indicated that the sample exhibits a hardness value that is similar to the values published in the literature. Using optical microscopy, the grain pattern of the polished samples shows a correlation between the sintering time and grain size. Overall, the results of this work show that the soaking time affects the grain size, and shape memory performance much more than it does to the hardness exhibited by the samples. furthermore, the process of pressureless sintering of pre-alloyed NiTi shape memory alloy powder can be an effective and efficient method for the fabrication of functional nitinol.