| Microwave sintering has been widely applied in the ceramic field as a new type sintering technology, but it was identified infeasible to preparation of the metal materials. Until1999, Roy et al reported the experimental results of metal powers sintered by microwave on Nature, and this technology immediately became the concern hotspot of the materials preparation field. However, using this technology to fabricate metal powder metallurgy materials are focused on the comparison with conventional sintering technology. The system and mechanism researches are very deficient. Against this background, in this thesis, the preparation of TiB2/Cu composites was considered as the research objects, the related microwave sintering process was explored with some emphasis, the dynamic mechanism of Cu powder and its compact under microwave field was discussed and the properties of the TiB2/Cu composites sintered by microwave was investigated, during which some achievements with theoretical and engineering significance on the microwave sintering of conductive metal powder metallurgy materials were gained.1. Various kinds effect factors of the Cu powder and TiB2/Cu composite powder compact sintered by microwave were systematically studied. The results show as follows:1) Under this experimental condition, the TiB2/Cu composites with different volume fraction of TiB2were successfully prepared through hybrid heating at1000℃for10min. The density of the samples was all higher than94%.2) Compared with the conventional heating sintering, the density of the samples sintered by microwave was much higher and the consumption of energy and time was substantially decreased.2. The microwave sintering dynamic mechanism of the spherical Cu powder and its compact was discussed. The results show as follows:1) The sintering process of Cu powder at the initial stage in hybrid heating mode the body diffusion mechanism was given priority, confirmed by the sintering of Cu powder in hybrid heating mode and the investigation of the growth up process of Cu powder sintered necks. The body diffusion activation energy was about256kJ/mol, consistent with those of the conventional powder sintering and the single microwave sintering, which indicated that the sintering behavior of Cu powder was the same under the three sintering modes.2) The sintering process of the Cu powder compact in hybrid heating mode was given priority to the body diffusion mechanism, confirmed by the investigation of grain growth rule. The body diffusion activation energy was about86.5kJ/mol, much lower than that of the conventional powder sintering, while consistent with that of the single microwave sintering. Therefore, the microwave sintering could improve the grain growth up, but the sintering behavior was the same between the hybrid heating and single microwave heating.3. Effects of TiB2contents and its surface modification on the electrical conductivity of the microwave sintered TiB2/Cu composite were studied. The results show as follows:1) the electrical conductivity of the TiB2/Cu composite decreased with increasing the TiB2contents.2) after the TiB2surface modified with chemical plating copper, all of the electrical conductivity of composite with the same TiB2content increased, and the increasing rate increased with increasing the TiB2contents, reaching the maxium value20.0%at10vol%TiB2.4. Effects of TiB2contents and its surface modification on the density of the microwave sintered TiB2/Cu composite were investigated. The results show as follows:1) the density of TiB2/Cu composite increased with increasing the TiB2contents, but the increase turned to unconspicuous after the TiB2content higher than5vol%.2) after the TiB2surface modified with chemical plating copper, the density of composite with the same TiB2content decreased.5. Effects of TiB2contents and its surface modification on the thermal expansivity of the microwave sintered TiB2/Cu composite were investigated. The results show as follows:1) the thermal expansivity of the TiB2/Cu composite decreased with inreasing the TiB2contents.2) after the TiB2surface modified with chemical plating copper, the thermal expansivity of the TiB2/Cu composite with the same TiB2content further decreased, but the thermal expansion behavior of the TiB2/Cu composite had not changed after particle modified with copper.3) the results of theoretical calculation showed that the thermal expansivity of the TiB2/Cu composite with no plating copper TiB2was consistent with ROM model calculation value, while the thermal expansivity of the TiB2/Cu composite with plating copper TiB2was consistent with Kerner model calculation value, which indicated that the interface of the TiB2particles and the matrix was greatly improved after the TiB2particles modified with plating copper.6. Effects of TiB2contents and its surface modification on the microhardness of the microwave sintered TiB2/Cu composite were investigated. The results show as follows:1) the microhardness of the TiB2/Cu composite increased with increasing the TiB2contents.2) after the TiB2surface modified with chemical plating copper, the microhardness of composite further increased, and the increasing rate increased with increasing the TiB2contents, reaching the maxium value13.1.0%at10vol%TiB2.7. Effects of TiB2contents and its surface modification on the wear resistance of the microwave sintered TiB2/Cu composite were investigated. The results showed as follows:1) the wear resistance of the TiB2/Cu composite increased with increasing the TiB2contents, and the wear mechanism changed from adhesive wear to abrasive wear and oxidative wear.2) after the TiB2surface modified with chemical plating copper, the wear resistance of the TiB2/Cu composite further increased, the biggest increase was about75.0%at10vol%TiB2, which indicated that the interface of the TiB2and the Cu matrix could greatly influence the wear resistance of the TiB2/Cu composite. |
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