Temperature dependence of irradiation-induced creep in dilute nanostructured Cu-W alloys

Irradiation-induced creep (IIC) in dilute Cu-W nanostructured alloy films, 300 nm thick, was measured as a function of temperature during 1.8-MeV Kr ⁺ irradiation using plane-strain bulge testing. The creep rate increased with increasing temperature between 300 K and 473 K, and then became constant up to 573 K. An activation enthalpy of 0.30 ± 0.05 eV was obtained for Cu _93.5W _6.5 and Cu ₉₉W ₁ alloys. Thermal creep, in absence of irradiation, became comparable to IIC at 573 K. Primary and secondary creep were observed at all temperatures. The steady state creep rate was proportional to the applied stress. Subsequent (scanning) transmission electron microscopy analysis revealed a high density of small (2-3 nm) W-rich nanoparticles with BCC structure after irradiation at all temperatures, but no dislocation loops. The average grain size of the irradiated alloys was stabilized at ∼30-40 nm in both alloys. Correlations between the microstructures and creep behaviors are discussed in terms of grain boundary creep mechanisms.