13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- thermal cycles its properties change (e.g., shape-recovery ratio, transformation temperatures, crystal structures, hysteresis and mechanical behavior). Cu–Zn–Al shape memory alloys exhibit shape memory behavior within a certain range of composition. It is characterized by a stable high temperature disordered bcc structure named β-phase. After a customized cooling process, a B2 structure is obtained followed a DO3 ordering. It is also know that martensite stabilization can be reduced by a step-quenched treatment. Cu ZnAl alloys mechanical properties are influenced by [5]: - martensite stabilization; - grain size; - processes procedure (e.g., temperature, heat treatment cycles number). Other investigations carried out on CuZnAl alloys, showed a strain influence on the macroscopic behavior and on martensite morphology. Martensitic transformation occurs initially in deformed material and the manufact shape follows the transformation [6]. Larger grains dimensions allow an easier transformation process, allowing the growth of 18R martensite [7]. In this work, damaging micromechanism during a tensile test in a CuZnAl alloy has been investigated, focusing the crack inititiation and its stable growth. Deformation influence on alloy microstructure has been investigated during the tensile test by means of X-Ray diffraction . 2. Material and methods In this work a CuZnAl pseudo-elastic alloy, made in laboratory by using controlled atmosphere furnace and characterized by chemical composition shown in Table 1, has been used to investigate mechanical behavior in tensile conditions. Table 1. Chemical composition of CuZnAl investigated alloy Cu Zn Al Other 73.00 21.80 5.04 0.16 The evolution of the microstructure during uniaxial deformation was analyzed by a miniature testing machine (Fig. 1) which allows in-situ scanning electron microscopic (SEM) observations as well as X-Ray micro-diffraction analyses. In particular, the testing machine is equipped with a simple and removable loading frame, which allows SEM and X-Ray analyses at fixed values of applied load and/or deformations. The machine is powered by a stepping motor, which applies the mechanical deformation to the specimen through a calibrated screw, with pitch of 0.8mm, and a control electronic allows simultaneous measurement and/or control of applied load and stroke of the specimen head. The stroke is measured by a Linear Variable Differential Transformer (LVDT) while the load is measured by two miniaturized load cells with maximum capacity of 10 kN. Miniature dog bone shaped specimens were machined from alloy samples obtained by cold cutting of mini sheets from as cast ingots, by wire electro discharge machining. Step by step isothermal tensile tests were carried out, at room temperature, at increasing values of
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