| In this thesis, nano-particles of Cu, Ag and Al were synthesized byflow-levitation method and filled into the mold at vacuum gloves chestunder the atmosphere of Ar in order to prevent oxidation. Subsequently,the nano-sized metal particles were compacted by use of exact hydraulicpress with cold-compaction and vacuum-warm-compaction technologyand nanocrystalline Cu, Ag and Al were prepared with relative density of96.7%, 98.1% and 98.5% respectively. The technology of preparation,microstructure and properties of such as-prepared nanocrystalline metalsmaterials were studied systematically and at close range. The results wereobtained as follows:(1) nano-particles of Cu were synthesized by flow-levitation method.The nano-particles prepared in Ar and mixture of 10%He and 90%Arwere globose with average grain size of 45 nm and 60 nm respectively.On the surface of the Cu particles, there were mixture of Cu2O and CuOand the atom ratio of Cu and O was 94.88:5.12, but the element of Ar andN were not found in the particles(include the residue after thermalanalyses).(2) The average grain size of nano-particles of Ag prepared in Heand Ar airflow were 15 nm and 80 nm respectively and the former issmaller. The particles were globose and the melting temperature was959.7℃, which was lower than the coarse grained Ag by 2.23℃.(3) The average grain size of globose nanoparticles of Al prepared inAr air flow was 50 nm. The content of O was 8.2% after preserved forhalf a year. The melting temperature of newly prepared nano-particleswas 649.7℃in Ar atmosphere. The element of N was found in theresidue after thermal analyses. But the element Ar was not found. Thisresult indicated that nano-particles of Al could have combined with N2during the heat process of thermal analyses.(4) As far as nanocrystalline Cu synthesized by cold-compactionconcerned, pressure had a profound influence upon the density and thedensity increased with higher pressure. The as-consolidatednanocrystalline Cu showed high thermal stability during the annealing process. The average grain size and microstrain of un-annealing specimenwere 19.9 nm and 0.233%. After annealing at 200℃for three hours, thatbecame 30.5 nm and 0.18%. The PAS analysis results showed that themost of the defects in the specimen after press was vacancies andvacancy-clusters; the amount of micro-voids is small. During theconsolidation, the amounts of vacancy-clusters growed while the amountof vacancies decreased and the amounts of micro-voids remainedunchanged.(5) The microhardness of the nanocrystalline Cu prepared bycold-compaction was 1.55～1.90GPa, exceeded that of coarse-grained Cuby the factors of 3～4. The electricl resistivity of nanocrystalline Cu wasabout 1.56×10-7Ω·m, which was about 9 times larger than that of thecoarse-grained Cu sample at room temperature. ICF simulationexperiment indicated that conversion efficiency of X-ray conversedfrom laser of as-prepared nanocrystalline Cu was 5 times higher thanthat of coarse-grained Cu. Nanocrystalline materials have brilliantfuture for application.(6) The microhardness of cold compacted nanocrystalline Al and Agwere 2.11GPa and 1.26GPa, which were higher than their coarse-grainedcounterparts by a factor of 14 and 2.5, respectively. The meltingtemperature of as-prepared nanocrystalline Al and Ag were 645.9℃and955.9℃, which showed lower melting temperature of nanocrystallinematerials. The electrical resistivities of the nanocrystalline Ag at roomtemperature are 1.475×10-7Ω·m and 1.5×10-7Ω·m, which are larger thanthe coarse grainedAg (1.59×10-8Ω·m) by a factor of 9.(7) With vacuum-warm-compaction method, nanocrystalline Cu, Ag,Al were prepared with relative densities of 96.15%, 99.66%, 97.9%,respectively. The microhardness of this three were 3.8 GPa, 1.25 Pa and1.65 Pa, which are higher than their coarse-grained counterparts by afactor of 8,3,and 5,respectively. It showed the property of highmicrohardness of nanocrystalline metallic material.(8) The nanocrystalline Cu showed high thermal stability. Theaverage grain size and microtrain of specimen of nanocrystalline Cu were25.3 nm and 0.047%, when compacted by vacuum warm-compacting method under 1.5 GPa and at 200℃for 1 h, respectively. The averagepositron annihilation lifetime r was 257.07ps, which was larger thanthat of un-vacuum-cold-compacted specimen by 36ps. This indicated thatthe microstructure of nanocrystlalline metals had changed during thecourse of vacuum-warm-compaction and at last, the dimension of themicro-vice became larger.(9) The nanocrystalline metals synthesized in this way had beenapplied primarily in physical experiment at present. This project has wonthe third-class Award of progress in Science and technology of PLA in2006.
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