Fabrication process and shape-memory effect of NiTi alloys synthesized from Ni/TiH2 powder mixture

An alternative powder metallurgical fabrication route for the production of NiTi shapememory alloys is presented. It uses TiH2 instead of Ti as raw powder. TiH2 powder was chosen because it has firstly the potential to decrease the oxide content of the final product due to the presence, in-situ, of hydrogen and secondly it is commercially available in very small sizes, thanks to its brittleness. NiTi alloys of two different chemical compositions were processed from elemental Ni, Ti and TiH2. The effect of TiH2 on the microstructure was investigated using X-ray diffraction, scanning electron microscopy, differential scanning calorimetry and shape-memory measurements. The alloys of near-equiatomic composition are single-phase NiTi. Ti-rich alloys show, in addition to the NiTi phase, a small quantity of Ti2Ni/Ti4Ni2Ox phases. The phase transformation enthalpies of the Ti-rich NiTi alloys are very close to those of reference melt-cast alloys. The samples exhibit substantial shapememory effects