13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Crack initiation and growth in an Zn-Cu-Al PE alloy Vittorio Di Cocco1,*, Francesco Iacoviello1, Luigi Tomassi1, Stefano Natali2, Valerio Volpe2 1 Department DICeM, University of Cassino and Southern Lazio, 03043, Italy 2 Department DICMA, University of Rome ―Sapienza‖, 00184, Italy * Corresponding author: v.dicocco@unicas.it Abstract Cu–Zn–Al shape memory alloys exhibit shape memory behavior within a certain range of composition. They are characterized by a stable high temperature disordered bcc structure named β-phase, followed by a transition to a B2 structure after appropriate cooling and from secondary B2 to DO3 ordering under other cooling procedures. It is also know that martensite stabilization can be reduced by a step-quenched treatment. Shape memory properties are often absolutely interesting and many grades of shape memory alloys are extensively used in the technological world, e. g. in surgery and dentistry. Copper-based shape memory alloys are preferred for their good memory properties and low cost of production. In this work, the main crack initiation and its propagation in an tensile test is analyzed in order to evaluate crack path and its behavior corresponding to low and to high deformation values. Furthermore, results are associated to X-Ray diffraction in order to correlate structural transition involved in an Cu-Zn-Al alloy characterized by a PE behavior. Keywords Shape Memory Alloy; Pseudo-Elastic Behaviour; Fracture; CuZnAl alloy. 1. Introduction Shape memory alloys (SMA) and pseudo-elastic alloys (PEA) are able to recover their original shape after high mechanical deformations: the first ones by heating up to characteristic temperature (Shape Memory Effect, SME), and the second ones simply by removing the mechanical load (Pseudo-elastic Effect, PE). Different shape memory alloys have been optimized in the last decades, such as the copper-zinc-aluminum (ZnCuAl), copper-aluminum-nickel (CuAlNi), nickel-manganese-gallium (NiMnGa), nickel-titanium (NiTi), and other SMAs obtained alloying zinc, copper, gold, iron, etc.. However, the near equiatomic NiTi binary system shows the most interesting properties and it is currently used in an increasing number of applications in many fields of engineering, for the realization of smart sensors and actuators, joining devices, hydraulic and pneumatic valves, release/separation systems, consumer applications and commercial gadgets [1, 2]. Due to their good biocompatibility, another important field of SMA application is medicine, where the pseudo-elasticity is mainly exploited for the realization of several components such as cardiovascular stent, embolic protection filters, orthopedic components, orthodontic wires, micro surgical and endoscopic devices [3]. From the microstructural point of view, shape memory and pseudo-elastic effects are due to a reversible solid state microstructural transition from austenite to martensite, which can be activated by mechanical and/or thermal loads [4]. Copper-based shape-memory alloys are very sensitive to thermal effects, and it is possible that in
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