13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- a) b) Figure 9. Fracture surface with high deformation: a) morphology of zone A of Fig. 8, b) morphology of zone B of Fig. 8. 4. Conclusions In this work, the main crack initiation and propagation micromechanisms during tensile tests performed on a CuZnAl SMA has been analyzed. According to the experimental results, the following conclusions can be summarized: - Cracks initiate at grains boundaries due both to high deformation values and to phases transitions; - Memory effect is not only due to phases transitions, but also to the unchanging of numbers of grins boundary; - The main fracture surface morphology is brittle and is characterized by intergranular cleavage; - Corresponding to the highest deformation values (―ending fracture zone‖) the main damaging micromechanism is ductile. 5. References [1] K. Otsuka, X. Ren, Physical metallurgy of Ti–Ni-based shape memory alloys, Progress in Materials Science (2005) 511. [2] Y. Dong, Z. Boming, L. Jun, A Changeable Aerofoil Actuated by Shape Memory Alloy Springs, Materials Science and Engineering A, 485 (2008) 243–250. [3] B. Chen, C. Liang, D. Fu, Pitting Corrosion of Cu-Zn-Al Shape Memory Alloy in Simulated Uterine Fluid, J. Mater. Sci. Technology, 21(2) (2005) 226-230. [4] Y. Liu, G.S. Tan, Formation of interfacial voids in cast and micro-grained γ′-Ni3Al during high temperature oxidation, Intermetallics (2000) 8 1385-1391. [5] P. Arneodo Larochette, M. Ahlers, Grain-size dependence of the two-way shape memory effect obtained by stabilisation in Cu–Zn–Al crystals, Materials Science and Engineering. A361 (2003) 249–257 [6] N. Kayali, S. Ozgen, O. Adiguzel, Strain effects on the macroscopic behaviour and martensite morphology in shape-memory CuZnAl alloys, Journal of Materials Processing Technology. 101 (2000) 245-249. [7] J.X. Zhang, Y.F. Zheng, L.C. Zhao, The Structure and Mobility of Intervariant Boundaries in 18R Martensite in a Cu-Zn-Al Alloy, Acta mater. 47(7) (1999) 2125-2141.
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