Microstructural studies of a Cu-Zn-Al shape-memory alloy with manganese and zirconium addition

Mn and Zr were added to improve the shape-memory characteristics of a Cu-Zn-Al shape-memory alloy (SMA). The microstructure of a Cu-19.0Zn-13.1Al-1.1Mn-0.3Zr (at. pct) alloy was examined using a transmission electron microscope (TEM). The structure of the parent phase and martensite phase are DO3 (or L21) and M18R1, respectively. Two kinds of Zr-rich precipitates formed in the alloy. Energy-dispersive X-ray spectroscopy (EDXS) analysis with a TEM indicates that the two precipitates are all new phases and have the compositions of Cu50.2Zr24.6Al17.3Zn7.9 (at. pct) (Z1 phase) and Cu57.4Zr20.4Zn10.3Al11.9 (at. pct) (Z2 phase), respectively. The volume ratio of Z1 phase in the alloy is about 70 pct of the total precipitate volume. The structure of Z1 phase was studied in detail using TEM electron diffraction analyses. The lattice parameter of fcc Z1 phase is a=1.24 nm, and the space group of the phase is F432 (No. 209). The Z1 phase possesses an incoherent interface with the parent-phase matrix. The lattice correspondence of the Z1 phase and parent-phase matrix is as follows: The effect of precipitate formation on the shape-memory characteristics of the Cu-Zn-Al-Mn-Zr alloy is discussed and compared to some other Cu-based SMAs.