Sintering of tungsten-copper composites of various origins

Abstract

In the presence of a liquid phase the most active sintering was exhibited by W-Cu composites produced from copper tungstate (43% Cu) and from an oxide mixture annealed in air (20% Cu). The reason for this was that air-annealing preceding reduction completely (composite 2) or partially (composite 4) transformed the mechanical mixtures of oxides into homogeneous compounds. Under these conditions the tungsten and copper were “mixed together” at an almost atomic level, which imparted a high degree of homogeneity and dispersion to the W-Cu charges after reduction. In compacts from such a charge a disperse structure with a copper matrix readily forms in the initial stage of sintering, and it is this structure that ensures a high rate of densification. The dependence of the degree of homogeneity of a W-Cu charge on method of preparation was found to be reflected in an increase in the mean pore size in the initial stage of sintering. As expected, the mean pore size grew only negligibly in the initial stage of sintering of compacts from the most homogeneous charges (composites 2 and 4), while in composites 5 and 6 the increase in pore size constituted a serious obstacle to macroscopic shrinkage.