IV ECCOMAS Thematic Conference on Smart Structures and Materials 1 1 INTRODUCTION Some materials have the ability to change shape or size simply by adding a little bit of heat, or to change from a liquid to a solid almost instantly when near a magnet. These materials are called smart materials (Grabe et al. 2009). Varieties of smart materials already exist and are being researched extensively. These include piezoelectric materials, magneto-rheostatic materials, electro-rheostatic materials, pH-sensitive materials, smart gels and shape memory alloys (SMA’s). The most known smart materials are SMA’s (Grabe et al. 2009). SMA's are metals that can be deformed and then returned to their original shape by heating. Arne Olander first observed these unusual properties in 1938, but not until the 1960's were any serious research advances made in the field of shape memory alloys. The most effective and widely used alloys include NiTi (Nickel - Titanium), CuZnAl, and CuAlNi (McNeese et al. 2000). The scientific and technological interest devoted to NiTi alloys is very high due to their unique properties such as mechanical shape memory (superplasticity, associated with high pure elastic deformability), thermal shape memory (related with shape recovery upon heating of the material), pseudo-plasticity (associated to the high bendability of the material without fatigue and fracture) and biocompatibility (related to the high corrosion resistance and excellent cytocompatibility). Several powder metallurgy techniques for producing NiTi alloys from elemental powders of Ni and Ti have been reported (Bram et al. 2002). Among these methods, mechanical alloying has attracted significant attention since it opened new avenues for the synthesis of metastable nanostructured and ultrafine grained materials (Gu et al. 2005). Recently, two innovative powder metallurgical processes named Mechanically Activated Reactive Extrusion Synthesis (MARES) and Mechanically Activated Reactive Forging Synthesis (MARFOS) were successfully set up for Ni–Ti alloys (Neves et al. 2007, 2008). 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 Characterization of smart MARFOS NiTi shape memory alloys F. Neves & F.M.B. Fernandes CENIMAT/I3N, Institute for Nanostructures, Nanomodelling and Nanofabrication, Monte de Caparica, Portugal F. Neves, I. Martins, J.B. Correia & M. Oliveira Department of Materials and Production Technologies-INETI, Lisboa, Portugal E. Gaffet Nanomaterials Research Group (NRG), Belfort, France N. Boucharat Materials Physics, University of Münster, Münster, Germany M. Lattemann, J. Suffner & H. Hahn Institute of Nanotechnology (INT), TUD – FZK, Karlsruhe, Germany ABSTRACT: 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.