Powder sintering and shape-memory behaviour of NiTi compacts synthesized from Ni and TiH2

The use of TiH2 to produce NiTi shape-memory alloys from elemental powders is investigated. Mixtures of Ni and TiH2 powders are cold-pressed and sintered in vacuum or under protective atmosphere. Some of the sintered NiTi compacts are subjected to an additional post-HIP treatment to further increase their density. Post-HIPped NiTi compacts with approximately 7% porosity are obtained. A detailed characterization of the microstructure of the compacts is carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. The phase transformation behaviour is studied by differential scanning calorimetry (DSC). The specimens present significant shape-memory effects. A recovery strain of up to 1.6% is reached under a stress of 120 MPa.