| Microwave sintering is a densification method through using the heating produced by the couple of microwave with the microstructure of materials and which have these features on bulk heating, selective heating and non-therm effect. It is a significant process capable of fabricating advanced materials with high performance and traditional materials with new properties. In this paper, the behaviour and mechnical of microwave heating pure metal powders was investigated, and the kinetics and mechanism of microwave sintering deoxidized ferrous powder was researched. The process, properties, microstructure and feature of microwave sintered Fe-Cu-C alloy, W-Ni-Fe alloy and WC/Co alloy are studied, and compared with conventional sintered alloy. Through these studies, we could know the microwave sintering characteristic on powder metallurgy materials. On the base of study, the major results of this paper are shown as following.(1)The mechnical of microwave heating metal powder existed electricity conducting loss, magnetism loss (eddy current loss, magnetism hysteresis loss, remain loss) and electron arc discharge loss. The sort of metal powders decided the effect degree of the microwave loss mechnical. The effect of eddy current loss, magnetism hysteresis loss and remain loss are obvious in magnetic materials, and electricity conducting loss is more in the materials with higher conductivity. The microwave heating therm profiles of same kind metal powders are dependent on partical size, porosity and output power. The little of partical size is, the faster of heating rate and higher of final temperature are. The larger of porosity is, the faster of heating rate is, but the final temperature don't depend on the porosity. And the higher of output power is, the faster of heating rate is. SiC is fast heated at low temperature and don't effect the Fe green heated at high temperature, so it is a ideal susceptor materials for metal green reducing the microwave heating time. (2) The relationship between microwave sintered densities and temperature of deoxidized ferrous powder with fcc structure was accorded with Huang Peiyun's synthesized sintering theory. The microwave sintering main mechanism of deoxidized ferrous powder is grain boundary diffusion, and there also exists volume diffusion. The apparent activated energy is 76.21 kJ/mol and it is close to conventional sintered.(3) Compared with the conventional sintering, the microwave heating rate is faster and reduce processing time for Fe-2Cu-0.6C steel alloy. Soaking time for 10min, Fe-2Cu-0.6C steel alloy sintered at 1150?via microwave irradiation has a superior properties. The as-sintered sample has a density, HRB, tensile strength and elongation up to 7.20 g/cm3,75,413.9 MPa and 6.0%, respectively. At temperature 1150?, Fe-2Cu-0.6C steel alloy sintered for 15min via microwave irradiation has a superior properties. The as-sintered sample has a density, HRB, tensile strength and elongation up to 7.22 g/cm3,78,416.8 MPa and 5.5%, respectively. In comparison with the conventional sintered, the microwave sintered sample has slightly low HRB and obviously high tensile properties. Sintering mode influences the pore morphology and porosity in the sintered alloy. Lower porosity, small and isolated pores are formed in the microwave sintered sample, in contrast with the large, connected and angular ones in conventional sintered counterpart. Flaky and granular pearlite plus ferrite are presented in the alloy after microwave sintering, different from the predominant ferrite and minor pearlite in conventional sintered sample. Microstructure discrepancy elucidates the different properties possessed by the sintered alloys. Fracture analysis indicates that microwave sintering generates a mixed fracture mode consisting of ductile and brittle manners, other than the single brittle one in conventional sintered sample.(4) The little of W particle size is, the higher of the properties of 90W-7Ni-3Fe alloy sintered at the same temperature are. On the contrary little particle has low performance at high temperature. There are optimal properties at appropriate temperature for every kind of sample. The A sample sintered at 1440?via microwave irradiation has tensile strength 919 MPa and hardness HRC35.8, and B sample at 1460?has tensile strength 899 MPa and hardness HRC34.5, then C sample at 1480?has tensile strength 884 MPa and hardness HRC34.5. Compared with conventional sintered, microwave sintered sample has more little distortion and more small and uniform tungsten grain. TEM shown that some local orient stripes were found in W-Ni-Fe alloy sintered via microwave irradition, it was the result of microwave non-therm effect.(5) Soaking time for 15min, YG8 cemented carbide sintered at 1500?via microwave irradition has a optimal properties. The as-sintered sample has a HRA up to 90.3. Compared with conventional sintered, microwave sintered sample had higher hardness and badly lower bending strength, it existed?phase and lost carbon in microwave sintering sample, and the same time WC grain dissolution-deposition is slow. Microstructural investigations showed that microwave sintered sample were small and uniform in grain sizes. The formation of?phase attributes to oxygen gas existed in the microwave sintering furnace. The samples sintered at 1460?WC-6Co has the maximum hardness, and WC-9Co has the best bending strength. Compared with WC-6Co sample, WC-3Ni-3Fe sintered via microwave irradition has low properties. |
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