NiAl shape memory alloy prepared by hot isostatic pressing

Abstract
NiAl can be a good shape memory material with high transformation temperatures. However, conventionally cast NiAl shape memory alloy (SMA) usually consists of huge columnar grains in the millimeter scale, which usually gives favorable an-isotropic mechanical properties. This bas limited the application of NiAl SMA. It had been reported that the grain size of NiAl SMA prepared by powder metallurgy is much smaller. However, the high porosity of the sintered NiAl from powder compacts had brought brittleness to the alloy. We prepared the NiAl SMA from elemental powders by mechanical alloying and Hot Isostatic Pressing (HIPPING). After HIPPING, fully densified NiAl alloy were made, which possess much better mechanical strength in the absence of high porosity. XRD crystallographic analysis revealed the presence of the martensite phase. Martensitic transformation was characterized by Differential Scanning Calorimetry (DSC) thermal analysis. With suitable heat treatments, the Af can be raised to 192°C. The phase transformation characteristics were found stable in the first 10 thermal cycles.