Investigation of In-Band Resonant Modes in Cr-W Alloys by Inelastic Neutron Scattering

Abstract

Transverse phonon groups in the [001] and [011] symmetry directions have been measured for Cr and three Cr-W alloys by inelastic neutron scattering using the triple-axis neutron diffractometer at the Missouri University Research Reactor. The tungsten concentration for the alloys are 0.3-, 0.8-, and 1.6- at.% W. The shifts in the phonon frequencies for each alloy showed the expected in-band resonant mode behavior. However, on extending the measurements of the shifts to the zone boundary in the [011] direction, additional structure was observed as well as a substantial increase in the magnitude of the negative shifts as one approaches the zone boundary. These frequency shifts are compared to the theory of Elliott and Maradudin using the frequency distribution function of chromium. The agreement between theory and experiment is no better for the lower tungsten concentrations than for previous results for Cr-3-at.% W. Thus, for the Cr-W system the mass-defect theory appears to be inadequate to predict the measured frequency shifts.