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Structure and hardness of nanocrystalline silver 总被引:5,自引:0,他引:5
Nanocrystalline silver (Ag) was prepared by in situ compacting of ultra-fine silver particles. The structures of as-compacted
and annealed specimens were analysed by high-resolution transmission electron microscopy and scanning electron microscopy.
Vickers microhardness was measured on the specimens. The ultra-fine particles aggregate before compaction. It is found that
the nanocrystalline specimens are obtained by the compaction of the aggregates. Microstructure inside the aggregates does
not change as the compacting pressure increases from 0.25 to 2.00 GPa. The compacting pressure affects on the structure and
density of the boundaries between the aggregates, i.e. the formation of the crack-type defects of about 1 μm at the boundaries.
Thermal stability of nanocrystalline Ag is significantly low; grain coarsening starts below 200 °C. However, a nanometre-sized
layered structure forms in local regions upon annealing and is stable up to 800 °C. Vickers microhardness of as-compacted
specimens increases with increasing compacting pressure. The increase is attributed to the decrease of the number of crack-type
defects. Vickers microhardness of nanocrystalline Ag begins to decrease due to grain coarsening upon annealing around 200
°C. The microhardness of nanocrystalline Ag deviates from the HalI–Petch relation.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
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