Incommensurate modulated structure study of a Cu–Zn–Al–Zr phase

Zr was added to Cu–Zn–Al shape memory alloy as a grain refinement element. There are two new phases, Cu 50.2Zr 24.6Al 17.3Zn 7.9 (at%) ( Z 1 phase) and Cu 57.4Zr 20.4Zn 10.3Al 11.9 (at%) ( Z 2 phase), in the Cu–19.0Zn–13.1Al–1.1Mn–0.3Zr (at%) alloy. The structure of the Cu 57.4Zr 20.4Zn 10.3Al 11.9 (at%) ( Z 2) phase is studied in detail in the present paper. The results of electron diffraction and high-resolution electron microscopy (HREM) investigations indicated a one-dimensional incommensurate modulated structure in the Z 2 phase. The average structure of the phase is base-centred orthorhombic. The systematic reflection conditions associated with the main and satellite reflections demonstrate that the Bravais class of the Z 2 phase is P Cmmm 11 1 type in a (3+1) dimensional space for the incommensurate modulated structure. The substitution modulation effects of the Al and Zr elements are revealed by energy-filtered transmission electron microscopy (EFTEM). { 1 3 ̄ 2 ̄ } compound-type twins are observed in the Z 2 phase. The relationship between the Z 1 and Z 2 phases in the alloy is discussed.