Creep properties of an extruded copper–8% chromium–4% niobium alloy

Constant-stress creep experiments were conducted on extruded Cu–8 Cr–4 Nb (GRCop-84) from 0.57 to 0.79 Tm, with observed strain rates spanning over four orders of magnitude. GRCop-84 is composed of approximately 14 vol.% Cr2Nb distributed in sizes ranging from approximately 30 nm to 0.5 μm in a matrix of pure copper with a grain size of approximately 1–3 μm. This high-strength alloy exhibits creep curves with a standard pure metal-type appearance and true failure strains typically in excess of 10%. The Monkman–Grant relationship is obeyed with a slope of −1.08. Computation of activation energies between neighboring isotherms yields an average value of 287±14 kJ/mol. Despite apparent power law creep behavior within an isotherm, a master plot of temperature compensated strain rate (ε̇/exp[−Q/RT]) versus temperature compensated stress (σ/G) demonstrates that most of the data are above power law breakdown, consistent with σ/G>̃10−3. A hyperbolic sine model facilitates interpolation on this master plot to stresses and/or temperatures where experimental data do not exist. Neither the threshold stress model nor the dislocation detachment model applies to GRCop-84 under these creep conditions.