Effect of liquid content on distortion and rearrangement densification of liquid-phase-sintered W-Cu

Abstract

Tungsten and copper exhibit negligible solubility for each other, so densification during liquid phase sintering of W-Cu is limited to rearrangement of the W particles and solid-state sintering of the W skeleton. Experiments are conducted to evaluate the effects of Cu volume fraction on liquid phase sintering of W-Cu. Sintered microstructures are quantitatively analyzed and are used to define critical microstructural parameters that prevent distortion and rearrangement densification. Slumping is prevented first by capillary forces, then by formation of a rigid W skeleton at critical values of contiguity and connectivity, which depend on the dihedral angle. A refined expression for the dependence of contiguity on volume fraction that includes the effect of the dihedral angle is developed. An analysis of gravitational, capillary, and bonding forces acting on W particles in liquid Cu explains the ability to achieve high sintered densities through rearrangement despite a lack of distortion with up to 80 vol pct liquid. Capillary forces are sufficient to break weak solid-solid bonds that form during heating, enabling rearrangement to occur even without dissolution of these bonds. At higher solid volume fractions, sufficient particle contacts form to prevent rearrangement by these capillary forces, thus limiting sintered densities.