| Copper matrix composites reinforced by Nano-Al2O3(p) can provide excellent performances such as high strength ,high electric conductivity ..anti-high temperature creep and resistance to wear, which have a broad application foreground in the field of electrotechnics, electronics and information technology. In the paper the densification properties of Cu-coated nano-Al2O3(p) compounds prepared by electroless copper plating have been researched by the method of pressureless sintering. In the meantime, aiming at reducing the aggregate and uneven distribution of nano- Al2O3(p) in the Cu-coated nano-Al2O3(p) compounds prepared by the past technics , the process of electroless copper plating have been carefully discussed and improved.The result of sintering Cu-coated nano-Al2O3(p) compounds prepared by the past technics indicated that pretreatment of electroless compounds significantly influenced on the densification properties of compounds. Cu-coated nano-Al2O3(p) compounds contained of a great deal of impurities ,which were brought by electroless copper plating and will be decomposed at a high temperature and consequently generate gaseous reactanfs .The electroless compounds pretreatment processes ,such as rinsing powders, reducing at H2 atmosphere and calcining at a high temperature can remove the disadvantageous influence of impurities.Comparing with ammonia and vacuum atmosphere , H2 atmosphere was highly advantageous to densification of compounds. Among sintering parameters, the forming pressure played much more important roles than those of the sintering temperature and holding time. The processes of repressing- resintering and a high forming pressure were in favor of improving density of the sintering sample.Increasing of the content of nano-Al2O3(p) holded back the raise of density of the sintering sample. Comparing with micro-Al2O3(p) , nano-Al2O3(p) coated by copper behaved more difficult densification effect. The reason was that the thickness of copper cladding was larger in the condition of microparticle and lower percentage composition of Al2O3 ,which made plastic yield took place easily. On the basis of optimizing parameters, the relative density of Cu nano-Al2O3(p) with norminal loading of 10 wt.% Al2O3 can reach 94% theoretic density via conventional powder metallurgy The main characteristic of sintering nano- Al2O3(p) coated by copper is two-phase sintering system which adsorbed organic impurities on the surface of powder ,and two-phase substances were insoluble each other. The key process of improving the quality of the sinter was to find an effective method which can remove the impurities adsorbed on the surface of the electroless plating powders.Aiming at the shortage of the former electroless plating process, the author improved on the plating process, including the use of two-step method in the pretreatment of nano- A1203 powders, replacing the drying process of pretreated powders with slurry process. On the base of improving pretreatment process, the modes of electroless plating were also discussed. The electroless plating powders were determined by laser diffraction particle size analyser (Beckman Coulter LS 311), high-resolution field-emission scanning electron microscope (AMARY-1910 FE) and thermogravimetric analyzer.The uniformity of nano-Al2O3 dispersed on copper matrix can be obtained by SEM .The result indicated that the pretreatment process of nano-Al2O3 powder, especially the coursing process, exerted a great influence on the disperse of electroless plating nano-Al2O3 powders. The reason was macromolecule dispersant ,which was joined with nano-Al2O3 in the fabricating course to improve suspending stability and reduced agglomerate of nano-Al2O3 powders in the suspending solution, will influence on the disperse of electroless plating nano-Al2O3 powders .In the four electroless plating modes-direct mixing mode,d ropping sodium hydroxide solution mode, dropping deoxidizing solution mode and dropping main salt solution mode, the last mode can obtain best laser diff... |
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