Tensile creep behaviour of coarse grained copper foils at high homologous temperatures and low stresses

Tensile creep behaviour of OFHC copper in the temperature range 850 to 1074°C (0·83 to 0·99T_m) under low stress (0·1 to 0·6 MPa) has been investigated in tension for 0·4 and 0·6 mm thick foils with grain size ∼1 mm, in the plane of the foils. Increases in creep rate per unit stress at 0·99T_m were two orders of magnitude higher than predicted for Nabarro–Herring diffusional creep and were nearer to values expected from the operation of grain size independent Harper–Dorn creep, but the stress exponent n was closer to 2 than to the n=1 expected in this mechanism. Observations on specimen surfaces revealed some widely spaced slip bands, some small grain boundary movements and occasional cavitation on grain boundaries nearly perpendicular to the stress. Creep rates were comparable with predictions of the movement of dislocations, controlled by the rate of their generation at Bardeen–Herring sources at a spacing similar to that of the observed slip lines.