Vacuum brazing studies

SIGLELD:9091.9F(AERE-R--10566) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

A Phenomenological Analysis of Sintering Mechanisms of W-Cu from the Effect of Copper Content on Densification Kinetics

International audienceThe effect of addition of copper on the sintering of a W powder was systematically investigated by the analysis of dilatometric experiments on W and W-Cu compacts prepared with submicrometric powders. A pure W powder compact and a W-10 wt pct Cu powder compact with the same packing fraction of W particles were first studied, in order to analyze the effect of copper at fixed microstructure of the solid W particle packing. A more systematic set of experiments with different copper contents and W particle sizes was also qualitatively analyzed. A phenomenological model of sintering was developed and fitted in order to extrapolate the effect of copper content on sintering kinetics at fixed microstructure of the W particle skeleton. An interpretation of the sintering mechanisms was then proposed. Sintering of a W-Cu powder compact is the result of solid-state sintering of the W skeleton, enhanced by the capillary forces exerted by copper, with the superimposition of a particle rearrangement step after copper meltin

Modeling the Capillary Pressure for the Migration of the Liquid Phase in Granular Solid-Liquid-Vapor Systems: Application to the Control of the Composition Profile in W-Cu FGM Materials

International audienceA model is developed to compute the capillary pressure for the migration of the liquid phase out or into a uniform solid-liquid-vapor system. The capillary pressure is defined as the reduction of the overall interface energy per volume increment of the transferred fluid phase. The model takes into account the particle size of the solid particle aggregate, the packing configuration (coordination number, porosity), the volume fractions of the different phases, and the values of the interface energies in the system. The model is used for analyzing the stability of the composition profile during processing of W-Cu functionally graded materials combining a composition gradient with a particle size gradient. The migration pressure is computed with the model in two stages: (1) just after the melting of copper, i.e., when sintering and shape accommodation of the W particle aggregate can still be neglected and (2) at high temperature, when the system is close to full density with equilibrium particle shape. The model predicts well the different stages of liquid-phase migration observed experimentally