Shape Memory Alloys- Processing, Characterization and Applications

Shape memory alloys have become in the past decades a well established research subject. But, the complex relations between properties and structure have created a continuously growing interest for a deeper insight during all this time. The complexity of the relationships between structure and properties is mostly related to the fact that strong "multidimensional" interactions are taking place: from the early studies focusing on the thermal and/or mechanical induced phase transformations to the more recent findings about the magnetically induced structural changes. On the other hand, these singular behavior characteristics have driven a great industrial interest due to the innovative aspects that the applications of shape memory alloys may provide. This makes this subject a highly attractive source of continuing studies, ranging from basics crystallography and thermodynamics to mechanical analysis and electrical and magnetic properties characterization. In this book, a group of recent studies is compiled focusing a wide range of topics from processing to the relationship between the structure and properties, as well as new applications. In the processing section, results are presented for special issues concerning the thermomechanical treatments of binary alloys and ternary alloys, namely using innovative techniques. The first paper details the changes of the transformation characteristics of binary alloys resulting from different variants of thermomechanical treatments, including severe plastic deformation. The second paper focus on the interest of going from binary to ternary alloys and the problems raised by innoative processing techniques. In particular, the Ni-Ti-Cu alloys hae attracted a great interest and the possibilities open by advanced technologies such as powder metallurgy and melt spinning are extensively reviewed in the third and last paper of this section. The relatively more recent interest on the Ferromagnetic Shape Memory Alloys opens new challenges in terms the characterization techniques combining thermal analysis and magnetic methods. This is the topic for the first paper of the section of characterization, where some alloys from the system based on Ni-Mn-Ga are studied. The singular properties of the shape memory alloys are strongly related to the thermomechanical behavior. A clear understanding of this type of situation requires the use of models, such as the one that is proposed in the first paper of the section on mechanical behavior. The second paper presents a model for hysteretic loops providing the basis for a finer analysis of thermal / mechanical cycling. Finally, the third paper provides useful information on the experimental approach to get a deeper insight on the link between micro and macromechanical behavior and its relation with the structural details. Iron based SMA are becoming very attractive engineering materials and their structura characterization is presented in the second paper. Finally, a section on applications presents two interesting papers focusing on two major engineering areas: civil and biomedical. Based on a constitutive model and thermal and mechanical characterization, a practical application of SMA on a smart concrete bridge structure is presented. Next, the combination of the superelastic and shape memory effect characteristics with the good biocompatility of Ni-Ti alloys is exploited in the field of biomedical engineering, namely for implants.