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V. Di Cocco et alii, Frattura ed Integrità Strutturale, 34 (2015) 415-421; DOI: 10.3221/IGF-ESIS.34.46 415 Focussed on Crack Paths Fatigue crack micromechanisms in a Cu-Zn-Al shape memory alloy with pseudo-elastic behavior Vittorio Di Cocco, Francesco Iacoviello Università di Cassino e del Lazio Meridionale, DICeM, Cassino (FR), Italy v.dicocco@unicas.it , iacoviello@unicas.it Stefano Natali, Andrea Brotzu Università di Roma “Sapienza”, D.I.C.M.A., via Eudossiana 18, 00184 Roma stefano.natali@uniroma1.it, andrea.brotzu@uniroma1.it A BSTRACT . Shape memory property characterizes the behavior of many Ti based and Cu based alloys (SMAs). In Cu-Zn-Al SMAs, the original shape recovering is due to a bcc phase that is stable at high temperature. After an appropriate cooling process, this phase (β-phase or austenitic phase) transforms reversibly into a B2 structure (transition phase) and, after a further cooling process or a plastic deformation, it transforms into a DO 3 phase (martensitic phase). In β-Cu-Zn-Al SMAs, the martensitic transformation due to plastic deformation is not stable at room temperature: a high temperature “austenitization” process followed by a high speed cooling process allow to obtain a martensitic phase with a higher stability. In this work, a Cu-Zn-Al SMA in “as cast” conditions has been microstructurally and metallographically characterized by means of X-Ray diffraction and Light Optical Microscope (LOM) observations. Fatigue crack propagation resistance and damaging micromechanisms have been investigated corresponding to three different load ratios (R=0.10, 0.50 and 0.75). K EYWORDS . Zn-Cu-Al alloy; Pseudoelastic behaviour; Fatigue Crack Micromechanisms; Microstructure. I NTRODUCTION hape memory property characterizes the behavior of many Ti based and Cu based alloys (SMAs). This property is due to a metallurgical phenomenon, which allows to change the lattice structure without boundaries changing as a reversible transition. Equiatomic NiTi alloys and Cu-Zn-Al alloys are among the most industrially used SMAs: they are characterized by two different mechanical behaviours in terms of shape recovering:  A shape memory effect (SME). This is obtained when the recovery of the initial shape takes place only after heating over a critical temperature, with a consequent crystallographic structure transition;  A pseudoelastic effect (PE). This is obtained when the critical temperature is lower than environmental temperature. In this case, the recovery of the initial shape takes place only after unloading. S