FABRICATION OF NITI SAMPLES USING PRESSURELESS SINTERING OF UNCOMPACTED METAL POWDER

Among the several metal systems capable of shape memory behavior, nickel-titanium (NiTi or nitinol) remains the most utilized. One way to fabricate nitinol components is by way of sintering of compressed elemental or pre-alloyed metal powder; a process that involves the design and use of an appropriate mold. This study investigates pressureless sintering of pre-alloyed NiTi powder, which eliminates the need for compaction to form a green part. The method involves preheating and sintering at an appropriate rate and time in a vacuum to achieve sintering of nitinol. After heat treatment, differential scanning calorimetry (DSC) thermograms reveal that the material exhibits shape memory performance through phase transformation peaks. Moreover, energy dispersive spectroscopy (EDS) is performed using scanning electron microscopy (SEM) to reveal a homogenous mixture of Ni and Ti. Brinell hardness test is used to demonstrate the qualitative performance of shape memory. Vickers hardness test revealed that the sample demonstrates a hardness value comparable to those reported in literature. Finally, micro-CT results demonstrating minimal porosity in the sample are presented. Overall, the results of this work show that pressureless sintering of pre-alloyed NiTi shape memory alloy (SMA) powder can be an effective and efficient method for the fabrication of functional nitinol. The elimination of the need for a mold to compress nitinol powder into a green part simplifies the fabrication process and reduces production cost. The structural homogeneity of the obtained samples and absence of easily distinguishable porosities further suggests that this method can result in high-quality NiTi samples.