LATTICE-DYNAMICAL STUDY OF THE PREMARTENSITIC STATE OF THE CU-AL-BE ALLOYS

Neutron-scattering techniques have been used to study the premartensit ic state of a family of Cu-Al-Be alloys, which transform from the bec phase to an 18R martensitic structure. We find that the phonon modes o f the TA2[110] branch have very low energies with anomalous temperatur e dependence. A slight anomaly at q = 2/3 was observed; this anomaly, however, does not change significantly with temperature. No elastic pe aks, related to the martensite structure, were found in the premartens itic state of these alloys. The results are compared with measurements , performed under the same instrumental conditions, on two Cu-Al-Ni an d a Cu-Zn-Al martensitic alloy.