High Temperature Tensile Ductility of Copper in Vacuum

Abstract

In order to correlate experimentally the temperature- and strain rate-dependence of the intermediate temperature embrittlement of copper with its grain boundary deformation behaviours and fracture modes, OFHC copper specimens were annealed to have grain diameters of 20, 80 and 180 μ and then tested in tension in vacuum. The testing temperatures and strain rates ranged from room temperature to 700°C and from 2.3×10−3 to 120/sec, respectively. Findings in the present experiments are summarized as follows. (1) The intermediate temperature embrittlement of copper occurred remarkably in vacuum as well as in air. (2) The ductility at a given temperature and strain rate decreased sharply with grain diameters between 20 and 80 μ, beyond which the ductility remained almost unchanged. (3) In a temperature range in which the embrittlement occurred, the fracture of the specimen stretched at a low strain rate (\simeq10−3/sec) was the intergranular one accompanied by microvoid coalescence, the mode of which was changd with temperature. At an intermediate deformation speed (\simeq10−1/sec), the specimen was fractured finally by a ductile fracture of matrices among large cavities originating from local separations of grain boundaries. The mode of fracture of the matrices was also changed with temperature. The fracture of the specimen tested at a very high speed (\simeq102/sec) was the transgranular one accompanied by microvoid coalescence.