Determination of the order in γ1 intermetallic phase in Cu–Al–Ni shape memory alloys

Stable phase precipitation produces deleterious effects in the characteristics of the martensitic transformation in shape memory alloys. In particular, the γ1 phase appears during heating as a primary precipitation previous to the eutectic reaction in Cu–Al–Ni alloys. Nevertheless the crystallographic structure of this γ1 phase in Cu–Al–Ni alloys is not well known. Neutron Powder Diffraction measurements have been performed at 546 °C in a Cu–27.4 Al–3.6 Ni at.% alloy where two eutectic phases α and γ1 have been identified. Rietveld analysis allows determining the positions and the site occupancy of the different atoms in the γ1 phase.