DETERMINATION OF TEXTURE COEFFICIENTS IN HEXAGONAL POLYCRYSTALLINE AGGREGATES WITH ORTHORHOMBIC SYMMETRY USING ULTRASOUNDS

A method to characterize the texture of hexagonal polycrystalline aggr egates with orthorhombic macroscopic symmetry is presented. Previous m ethods are extended to the analysis of waves propagating on three prin cipal planes of the material. Five coefficients of the crystallographi c orientation distribution function, W-200, W-220, W-400, W-420, and W -440, are determined from angular variations of the phase, velocity of the five ultrasonic modes considered: Bulk longitudinal waves, shear waves with in-plane and plane-normal polarizations, Rayleigh surface w aves, and the fundamental symmetric plate mode (in the long-wavelength limit). Analytical expressions for the texture coefficients are found for an arbitrary number of principal planes. Measurements are reporte d for a Zr-2.5% wt Nb pressure tube; an alloy used in CANDU nuclear re actors. The angular variations of the phase velocity of leaky Rayleigh waves and leaky surface skimming compressional waves are measured wit h a line-focus acoustic microscope. Although these waves are not exact ly those treated in the theory, they are closely related to pure Rayle igh waves and bulk longitudinal waves. The determined texture coeffici ents are sensitive to the input physical parameters when certain combi nations of planes and acoustic waves requiring absolute velocity measu rements are used. However, the coefficients are less sensitive to the input parameters when combinations requiring only relative velocity me asurements are used. Results derived from relative measurements agreed with neutron scattering measurements.