Theory and technology of sintering, thermal and chemicothermal treatment - Densification of WC-Co alloys in solid-phase sintering (review)

The studies on the densification of WC-Co alloys in solid phase sintering are analyzed. It is shown that solid phase sintering of alloys with tungsten carbide particles smaller than 2.0 mu m is characterized by high densification (shrinkage) and results in compact samples in some cases. Shrinkage is established to be nonmonotonic over a wide range of sintering temperatures. There are at least three different stages of densification over the range from room to solidus temperatures. Approximate temperature ranges for densification stages are 100 to 1050 degrees C, 1050 to 1200 degrees C, and 1200 degrees C to the eutectic melting temperature. The stages mainly differ in the extent and rate of shrinkage and in the activation energy. The compaction stages are separated by characteristic temperatures. The most important is 1200 degrees C, which separates the second and the third stages. The maximum rate of shrinkage is observed mostly at this temperature. The variation of initial WC particles from 5 to 2000 nm does not significantly affect the temperature at which the solid phase shrinkage rate is maximum. In most cases, there are two maximum rates of shrinkage in WC-Co sintering: one at 1200 +/- 30 degrees C and the other at the solidus temperature.