Study of martensitic transformation in AuCd alloys by means of neutron scattering and X-ray scattering

Abstract

AuCd alloy is a typical alloy which shows the martensitic transformation. There are two distinct martensitic phases close to the equi-atomic composition; one is called ζ2 and another is γ′2 phase. The crystal structures of the martensitic phases were determined and the transformation mechanism was derived from the results of the structure determination. The neutron inelastic scattering experiments were performed for both alloys. The phonon softening was observed at ζ = 0.35 in the [ζζ0]TA2 branch for Au50.5Cd49.5 and at the Brillouin zone boundary for Au52.5Cd47.5 alloys. In addition to the zone boundary softening in Au52.5Cd47.5, the softening at ζ = 0.35 was observed. Elastic scattering measurements were also performed for both compositions. The integrated intensities in Au50.5Cd49.5 were measured above the martensitic transformation temperature, M s, by X-ray diffraction. The decrease of the integrated intensities occurred with approach to M s. These phenomena are discussed from the view point of the transformation mechanism.