Investigation of the two martensitic phase transitions hcp-dhcp and dhcp-fcc in Co-0.85at%Fe by neutron scattering

Upon heating, Co-0.85at%Fe undergoes the two martensitic phase transitions hcp-->dhcp (at similar to 590 K) and dhcp-->fcc (at similar to 690K). The t ransitions are characterized by a large hysteresis permitting to investigat e properties of two phases at the same temperature, respectively. The dista nce between neighboring close-packed planes remains virtually constant duri ng the hcp-dhcp transition while a change of similar to 0.3% is observed at the dhcp-fcc transformation. The lattice dynamics of Co-0.85at%Fe was inve stigated by means of inelastic neutron scattering at a series of temperatur es up to 750 K in order to look for precursor effects in the phonon dispers ion curves near the two martensitic transformations. In all of the phonon b ranches investigated, anomalies were neither found near the hcp-dhcp nor th e dhcp-fcc transition. Both transformations in this system occur slowly and with a continuous change of the volume fractions of the phases involved ov er periods of several hours. (C) 1999 Elsevier Science S.A. All rights rese rved.