Nanocrystalline Cu with average grain size of 22.8-25.3 nm was prepared by vacuum-warm-compaction method. Scanning electronic microscope,HMV-2 type microhardness tester,X-ray diffractometer,and 6157 type electrometer were used to determine the microstructure,microhardness and electrical resistivity of as-prepared nanocrystalline Cu,respectively. The results show that the microhardness of nanocrystalline Cu increases with larger pressure,longer duration of pressure or higher temperature. The highest microhardness of nanocrystalline Cu is 3.8 GPa,which is 7 times higher than that of coarse-grained copper. The electrical resistivity of as-prepared specimens is(1.2-1.4)×10-7 -·m at temperature 233-293 K,which is 5-6 times higher than that of the coarse-grained copper.
The micrometer-sized Cu powder produced on commercial scale was compacted under pressure of 1.0?2.0 GPa and at room temperature,and the nanocrystalline(nc) Cu with diameter of 10 mm and thickness of 8 mm, relative density of 99.4% of the theoretical density for pure Cu (8.96 g/cm3), and mean grain size of 34?43 nm and microstrain of 0.16%?0.19% was obtained. The compacting process was analyzed with HUANG Pei-yun equation and the microstructure and properties of nc Cu were studied by XRD, SEM, PAS, MHV2000 mircrohardness tester and Datron 1081-type electrometer. The results show that the grain size of nc Cu samples is correlated with compacting pressure, the microhardness is 1.14?1.27 GPa which is about two times larger than that of the coarse-grained polycrystalline Cu, but the relationship between microhardness and grain size do not obey Hall-Petch equation strictly. The electrical resistivity of the specimens is 5.1×10?7Ω·m, larger than the coarse-grained Cu materials by a factor of 29, the mean lifetime of positron-annihilation is (172.8±0.8) ps. The cost of the method of fabrication for big-sized nc material is much lower than that of any others. This method has the advantages such as the lowest cost, largest output and volume as well as highest density over all other methods so far.
