Study On Properties Nanocrystalline WC-TiC-Co Cemented Carbide

This paper has manufactured nanocrystalline WC-TiC-10Co composite powders generated by ball-mill in the ethanol with 220r/min rotation, and the ratio of balls and powders is10 to 1,with average particle of micrometer WC TiC and Co powder at2.96μm. With the nanocrystalline WC-TiC-10Co composite powder sifted, the nanocrystalline WC-TiC-10Co pressing-blocks were pressed by Die pressing and Cold isostatic pressing, and pressing stress , keeping time and density were studied. The pressing-block were sintered with different sintering technics, and the relation between sintering temperature, shrinkage rate and pressure strength, and researched their microstructure, research found:1 The ratio of average particle at milling-time less than 60 hours is slowly 2.95μm to 0.61μm, and the particle uniformly distributing present grainy or strip. And it is clearly that some of the nanocrystalline WC-TiC-10Co composite powders are agglomerated, when milling time are more than 60h. The average particle size of nanocrystalline WC-TiC-10wt%Co composite powder generated by ball-mill in the ethanol is less than 50nm by SEM.2, Rate of pressing have no effect on the pressing-block density. When compressor didn't press the powder, the 3.0mm/s rate of pressing is equal to the ratio disrepair. And the 2.0mm/s rate of pressing is equal to the pressing-block density. The keeping-time is 2min, not oily efficiency is high, but also the pressing-block density is high.3 With pressing-block pressing in the glove vacuum box, the pressure strength of pressing-block pressed again at Cold isostatic pressing is 130.5MPa. But pressure strength of pressing-block commonly pressed is 108.1MPa, and pressing stress is 354MPa. With the press transferring uniformity by Cold isostatic pressing, the density of pressing-block is 7.3 g/cm~3, on account of rudimental hole cleared away by Cold isostatic pressing. But common pressing is 426.9MPa, the density of pressing-block is 7.1 g/cm~3, relative density is 55.3%4 With sintering temperature increasing, the density of sintering-block is increasing. The density is 10.9 g/cm~3 at sintering temperature of 1300℃. The density is 11.9 g/cm~3at sintering temperature of 1350℃. The density is 12.3 g/cm~3at sintering temperature of 1400℃. When the sintering temperature is among 1300-1400℃for nanocrystalline WC-TiC-10Co cemented carbide, the change of rigidity is little. The rigidity at sintering temperature 1300℃is 95.2 HRA. The rigidity is 94.9 HRA at sintering temperature 1350℃. The rigidity at sintering temperature 1400°C is 95.4HRA. But the rigidity for conventional cemented carbide is 89.5 HRA, so the rigidity for nanocrystalline WC-TiC-10Co cemented carbide is higher than for conventional cemented carbide.5 With sintering temperature among 1300℃to 1400℃, density of sintering-block increase from 10.9 g/cm~3 to g/cm~3(relative density 95.4%). With sintering temperature at 1480 for conventional cemented carbide, the density of sintering-block is 12.5g/cm~3(relative density at 97.3%). So sintering temperature for nanocrystalline WC-TiC-10Co cemented carbide is lower than for conventional cemented carbide.6 The structure for nanocrystalline WC-TiC-10Co cemented carbide by optical microscope are (TiW)C+ WC+γ+ηphase. The strength of nanocrystalline WC-TiC-10Co cemented carbide decline due to theηphase, theηphase avoid in the sinter. Crystal unconventionality grow up in the sinter bring on the strength declining, the essential technical measure were adopted for fine crystal.7 Seen from macro view, the break furface of nanocrystalline WC-TiC-10Co cemented carbide looks flat and brightess, belongs to brittleness rupture, and the mode of rupture is along crystal rupture. SEM photographs of nanocrystalline WC-TiC-10Co cemented carbide bending resistance specimen has apparent model nest, which shows that the sample occurs definite madel distortion.8 Sintering mechanism for nanocrystalline WC-TiC-10Co cemented carbide by thermochemistry and dynamics analyzed follow all the same sintering liquid theory. The sintering processes were three phases. First phase is liquide growing and grain recompositio. Second phase is solid dissolve and separate out. Then phase is sintering solid.