US Patent 7041250 Combined liquid phase and activated sintering of refractory metals

A process for producing a binder phase free fine grained refractory metal compact at temperatures that are less than about 80 percent of the melting point of the refractory metal. A refractory metal is mixed with a metallic reagent to produce a mixture with a low melting point, and formed into a preform. The metallic reagent has limited solubility in the solid phase refractory metal. The refractory metal-metallic reagent mixture forms a liquid phase at the boundaries of the refractory metal grains. The metallic reagent diffuses into the boundaries of the refractory grains leaving a solid refractory-reagent phase at the boundaries between the grains. As heating continues at less than about 80 percent of the melting point of the refractory metal, consolidation takes place with minimum grain growth until the solid refractory-reagent phase substantially disappears and a refractory metal compact without a binder phase is recovered. If the refractory metal-metallic reagent preform is compacted to less than about 50 percent of theoretical density, it is possible to recover a microporous compact. At higher compaction rates substantially fully dense compacts are recovered. It is not necessary to apply pressure during the sintering phase.