STRAIN-RATE AND GRAIN-SIZE EFFECT ON SUBSTRUCTURES AND MECHANICAL-PROPERTIES IN OFHC COPPER DURING TENSION

The combined effect of grain size (recrystallized grains of 34, 86, 10 5 and 128 mu m) and strain rate (0.01, 0.05, 0.25, 2.5 and 5 min(-1)) on the evolution of dislocation substructures and mechanical propertie s in oxygen-free high conductivity (OFHC) copper during room-temperatu re tensile testing has been studied. Under identical conditions of def ormation, the flow stress values for smaller grain size were higher th an those for larger grain sizes with the exception in the case of 86 m u m which has been attri buted to the in homogeneous substructural dev elopments in the microstructures. The cell size decreases monotonicall y with increase in per cent strain indicating no signs of cell size sa turation. The effect of strain rate on the development of dislocation substructures at constant strain is such that the cell size decreases initially but increases with further increase in strain rate for small er grain sizes of 34 and 86 mu m while a reverse trend has been observ ed for larger grain sizes of 105 and 128 mu m. A graph of the cell siz e strengthening coefficient, k, and the strain rate shows three distin ct stages in the curves for different grain sizes.