Characterization of smart MARFOS NiTi shape memory alloys

In the present study, structural characterization of NiTi smart shape memory alloys (SMAs), produced by an alternative powder metallurgy approach named mechanically activated reactive forging (MARFOS), was carried out by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was observed that MARFOS materials had a multiphase nanocrystalline structure. In addition, the transformation behaviour associated with the shape memory effect of the MARFOS aged materials was studied with differential scanning calorimetry (DSC). Multiple-step martensitic transformations could be observed in aged materials. These two new approaches comprise a mechanical activation step (i.e. a short duration ball milling step) of elemental Ni and Ti powder mixtures, a densification step and a homogenization heat treatment step. With MARES and MARFOS the synthesis of Ni–Ti intermetallics was achieved at lower temperatures through a controlled synthesis reaction, instead of the usual strong exothermic reaction between elemental Ti and Ni powders. However, the characterization of the materials has been made using essentially X-ray diffraction and scanning electron microscopy analysis. In this work, MARFOS NiTi alloys are also study by transmission electron microscopy and the transformation behavior associated with the shape memory effect is studied by differential scanning calorimetry.