Thermal activation analysis on the bubble-strengthening mechanism at high temperatures in [formula omitted] tungsten fine wires

Abstract

The doping elements such as Al, K and Si in P/M tungsten develop many arrays of small bubbles, the diameter of which ranges from 10 to 150 nm depending on annealing temperatures, along the wire axis during fabrication. In the present work, the authors consider the effects of bubbles on the flow stress at high temperatures from a point of view of thermal activation process of dislocation motion. The small activation energy for steady state creep in doped wire results from a combination of the effect of grain boundary cavitation on creep rates and the deformation of the constraining surroundings which is controlled by the Peierls-Nabarro mechanism. The elementary process of steady state creep in non-doped wire is the surface diffusion which rate-controls the grain boundary sliding. The increase in flow stress of doped wire must result from the athermal strengthening due to bubbles which block the climb of dislocations.