A. V. LaptevUDC 621.762.5The 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 μm 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°C, 1050 to 1200°C, and 1200°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°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°C and the other at the solidus temperature.The production of hard WC-Co alloys is based on liquid-phase sintering of prepressed powder compacts. This process ensures dense and quite strong products and, therefore, is widely used all over the world. The liquid-phase sintering of WC-Co alloys dates back to the 1920s and is still in use without fundamental changes. However, attempts to produce samples with better mechanical properties by forming a fine-grained structure have shown that the liquidphase sintering technology has a major drawback such as intensive growth of carbide particles while the mean size of WC particles is smaller than 1.0 µm. Note that this drawback had been revealed as early as the 1930s [1] and was dealt with by introducing additional components (tantalum, vanadium, chromium carbides, and so on) into the powder charge to inhibit the growth of tungsten carbide particles. This method seems to be quite efficient since it is still used in the production of fine-grained hard alloys.However, this unique method to deal with the active particulate growth turned out to be of little use in sintering of superfine powders. In particular, according to [2], conventional inhibitors fail to suppress the growth of tungsten carbide particles if they are smaller than 0.2 or 0.3 µm. This implies that newly developed nanocrystalline powders of cobalt and tungsten carbides [3] cannot be successfully used to produce hard alloys of higher quality. This is an obvious reason for the current attempts to develop technologies alternative to liquid-phase sintering. The greatest expert attention is paid to the consolidation of powders at low temperatures; in particular, solid-phase sintering of tungsten carbide alloys. Since solid-phase sintering precedes liquid-phase sintering, the former was the subject of some earlier studies [4][5][6][7][8]...
