Gibbs-Thompson Effect as Driving Force for Liquid Film Migration

Abstract

Liquid film migration is of great practical importance in materials engineering. The phenomenon depends on thermal gradients and coherency strain, but no single driving mechanism seems capable of justifying all experimental observations. On the other hand, the inevitable capillarity effects are often indeterminable due to the unknown three-dimensional geometry of the system. Here, we present evidence of liquid film migration governed primarily by the Gibbs-Thomson effect through a microstructural setup of cylindrical interfaces designed to allow clear interpretation and modeling. The experiment relies on the strong oxygen-gettering ability of tantalum fibers dispersed in a tungsten matrix and on field-enhanced diffusivity provided by pulse plasma compaction. Tantalum scavenges residual oxygen present in the W powder and, as a result, oxide films grow around the fibers. These oxide tubes, in liquid state during sintering, migrate toward the fiber axis and become surrounded by external rims of metallic Ta. An analytical description of the film evolution is implemented by combining the incoming O flux with capillarity driven migration. P ossible contributions from other mechanisms are examined and the r elevance of the Gibbs-Thomson effect to liquid film migration is established .