High Performance Tungsten Carbide Prepared by Microwave Sintering Technology

In all kinds of sintering technology, microwave heating with heating speed, the overall heating, selective heating and non-thermal effects of traditional heat conduction heating methods do not have the characteristics. WC-Co powder compacts have good coupling absorption to microwave, and the penetration depth of microwaves in the compacts of the mixture is very large. Therefore, the preparation of high-performance tungsten carbide by microwave sintering technology has the traditional heat conduction heating preparation method Unmatched advantages. These advantages are shown in the following aspects: 1, micro-high-performance wave heating fast, holistic not only can significantly shorten the preparation cycle and reduce the sintering temperature, simplifying the process, and can prepare a uniform microstructure, grain Small material. 2, because of the high energy efficiency of microwave and its environment-friendly features, it can at lower cost and less environmental pollution to create greater economic value. 3, the characteristics of microwave heating is very conducive to the development of nano-fine grain hard alloy, gradient cemented carbide, carbide coating and other new high-performance carbide. These advantages make the development of tungsten carbide and microwave sintering technology combined into an inevitable trend.

The WC-Co high performance tungsten carbide was successfully prepared by microwave sintering at the University of Pennsylvania. Compared with the traditional sintering method, microwave sintering can obtain the same degree of shrinkage at lower sintering temperature and shorter holding time. The sintered samples have the same degree of shrinkage in the three dimensional direction, while the traditional sintering method in the vertical direction And the microwave sintered samples have more fine WC grains and more uniform Co phase distribution than the traditional sintered samples. The hardness is higher and the chemical corrosion performance is better. In addition, it was found that there were almost no W atoms in the bonding phase of microwave sintered samples, which was very different from the case of the traditional sintered samples with about 20 wt% W atoms.

Dortmund University of Germany, using W, C and Co mixed powder crushed to microwave sintering, compared to the traditional process of WC and Co mixture briquette sintering, this process not only the synthesis of WC powder and WC-Co green compact Sintering two steps together, effectively simplifying the process, shortening the production cycle of cemented carbide, but also make full use of the carbon atoms in the WC between the release of heat, reducing the energy consumption of sintering. The high-performance tungsten carbide materials obtained by this process are denser, the organization is more compact, and the mechanical properties are improved.


 

The results show that the pure magnetic field heating can not complete the post-sintering of the alloy, because at 1100 ℃ above, the Co in the alloy will change from ferromagnetism to paramagnetism, so that the magnetic field can absorb the microwave magnetic field collapse, so that the magnetic field loss to temperature The sintering temperature of the alloy sample can not be increased continuously. However, WC-Co cemented carbide induction of microwave electromagnetic field mainly in the form of dielectric loss, therefore, the use of pure electric field and electromagnetic hybrid field heating can complete the whole densification of the alloy, and the prepared alloy has a good mechanics The WC grains in the microstructure are uniform, and the Co phase is evenly distributed, forming a good lattice structure.

In addition, for the decarburization in the sintering process, studies have shown that by adding carbon black in the mixture and adding carbon black in the filler can inhibit this decarbonization phenomenon, thereby enhancing the performance of microwave sintered cemented carbide. The results show that when the amount of carbon black is 0.4% (mass fraction), the flexural strength of the alloy is up to 2250 MPa. When the carbon black is added into the filler, the bending strength can be increased to 3172 MPa.

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