The activities between the US and Spain involving Dimitris Lagoudas, Ibrahim Karaman, and Raymundo Arroyave (Texas A&M University) with Eduard Cesari and Jaume Pons (Univ. Illes Balears – Palma de Mallorca, Spain) started in 2010, and continued in 2011. From the collaboration between University of Balearic Islands and Texas A&M University two main activities can be pointed, as follows:
The collaboration with Dr. Ibrahim Karaman based on the development of Ni-rich Ni-Ti-Zr and Ni-Ti-Hf High Temperature Shape Memory Alloys (HTSMAs) which is a systematic study of thermal treatments to improve the alloy performances has been done at MESAM (TAMU) research group. A remarkable improvement in martensitic transformation (MT) reproducibility as well as raise of transformation temperatures has been achieved. The corresponding microstructural characterization by TEM/HRTEM and related techniques has been performed at UIB. The precipitation of a new phase, different than the typical precipitates formed in Ni-rich Ni-Ti binary alloys, has been observed. The changes in MT caused by the precipitates can be interpreted in terms of precipitate size and interparticle distances. Intense work has been devoted to clarify the crystal structure of this precipitated phase, by means of electron diffraction and HRTEM imaging and simulations. A preliminary structural model for this phase has been built up.
The collaboration with Dr. R. Arroyave has the same main topic as the research made with Dr. Karaman; however, Dr. Arroyave performed Density Functional Theory (DFT) calculations for the proposed structural model of precipitates. The preliminary results about energetics of the new phase, compared to the austenite B2 matrix, reveal a good reasonability of the model, although some relaxation in atomic positions are needed to reach the energy minimum. Additional calculation of elastic constant tensor, charge transfer and electronic density of states (DOS) make sense to the proposed structure as well. New HRTEM image simulations in the relaxed model issued from DFT calculations will be performed at UIB. Anjana Talapatra, a student in Dr. Arroyave’s group will be visiting UIB during June to collaborate in the experimental and computational characterization of these intermetallic compounds.