| Summary: | The deformation and fracture behaviour of polycrystalline copper matrix with and without silica particles was investigated by testing at tensile strain rates of 0.0004 s-1 and 0.004 s-1 over the temperature range of 250-900 °c and by examining the fractured specimens by light and electron microscopy. The silica particles were introduced to the copper by internal oxidation of dilute copper-silica solid solutions (0.02-0.22 wt. % Si). The evolved silica particles were uniformally distributed throughout the lattice. Silica particles within the grains had radii in the range of 0.04-0.157 micron and spacing range of 0.3-0.64 micron and those located at grain boundaries had radii in the range of 0.31-0.34 micron and spacing range of 1.3-3.4 micron. In all cases, UTS decreased with increasing temperture and decreasing strain rate. This behaviour was interpreted in terms of the cocept of thermal activation process. The calculated thermal activation parameters (activation enthalpy and activation area) indicated that the rate controlling process, in the present results, was the non-conservative motion of jogged screw dislocations. Fracture, in all cases, was mainly caused by initiation, growth and interlinkage of triple point and grain edge cracks. Hot ductility was observsd to decrease with increasing temperature up to 0.6 Tm. Above this range the ductility increased only whenever dynamic recrystallization occurred. No considerable direct effects of silica particles on the deformation and fracture behaviour of polycrystalline copper were noted. Nevertheless, a preliminary experiment on the isothermal annealing behaviour of such material showed that silica particles enhanced static recrystallization of copper. In contrast silica particles decreased the rate of dynamic recrystallization that occurred during tensile deformation.
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