Low temperature creep ductility of OFHC copper

Creep tests have been carried out on oxygen-free high conductivity (OFHC) copper between 75 and 245°C. Two of the batches exhibited poor ductility at temperatures between 180 and 245°C and ruptured at creep strains of <1% while the third batch produced acceptable ductility values of ≈10% elongation at fracture. A general reduction of the ductility with increasing temperature has previously been observed (see the Ashby maps). The very low ductility (<1%) is however a new phenomenon and is attributed to an observed segregation of sulphur to the grain boundaries, possibly in combination with a large grain size. The test results approximately satisfy the Monkman–Grant relationship. Since the creep rates of the three batches were similar, the batch with the higher ductility also showed considerably longer rupture life. A creep ductility below 1% severely limits the use of OFHC copper at elevated temperatures and an intended application in canisters for spent nuclear fuel is not possible.