A phenomenological understanding of the influence of processing methods on creep of Cu-8Cr-4Nb (GRCop-84)

Steady-state creep behavior of rolled Cu-8Cr-4Nb (GRCop-84) production sheet was systematically studied at temperatures from 673 to 1073 K (0.50-0.79 T-m). Threshold behavior was observed at high temperatures and low stresses which can be phenomenologically described by a threshold stress model. The threshold stress obtained by a non-linear regression method ranges from 0.2 to 0.3 of the Orowan stress, which suggests that dislocations locally climb over particles with an activation energy approximately equal to that of lattice diffusion. Power-law breakdown was observed at low temperatures and high stresses, which can be phenomenologically described by a hyperbolic sine model. A unifying model is proposed to predict the creep properties of both the production sheet and previously-studied extruded material. Generally, GRCop-84 production sheet creeps faster than the extruded form due to the difference in crystallographic texture. No observable effects caused by microstructural differences are noted to influence the steady-state creep behavior of the two differ. ently processed forms of GRCop-84. The post-fracture morphology of the production sheet closely resembles that of the extruded material indicating ductile fracture caused by micro-void coalescence.