The rate of bubble deformation during tungsten wire drawing

Abstract

Rods and wires from K–Al–Si doped tungsten containing residual porosity and K filled bubbles were studied from 6 to 0.2 mm in diameter ( d) by means of anisotropic small angle neutron scattering (ASANS) method. This novel technique has been developed for monitoring shape and size of microscopic pores, bubbles, second phase particles in deformed PM materials. In case of mixture of different populations, e.g. uniformly elongated bubbles and spherical ones in tungsten, the morphological parameters for each population can be obtained from the quantitative analysis of ASANS data. Such parameters are: relative number density, diameter, aspect ratio of elongation. It was found that during wire drawing the average aspect ratio of elongated bubbles increases much slower (∼1/ d) than it was expected from the usual theory (∼1/ d 3). Instead of “constant volume” assumption, a “constant length” assumption seems to be reliable. The occurrence of spherical bubbles after several steps of wire drawing can also be revealed.