High temperature creep in copper

Abstract

Creep in copper of 99·99% purity in the temperature interval 550-1025°K was investigated by the isothermal tests technique. Two dislocation mechanisms operating in parallel were detected. In the region of lower creep rates-Region 1-the apparent activation energy of creep depends linearly on stress: [image omitted] where Q01 = 47·4 ± 2·8 kcal mol-1 and B1 = 3·2 ± 0·5 kcal mol-1 Kg-1 mm2. The value of Q01 is close to the activation enthalpy of lattice self-diffusion in copper. Consequently, creep is controlled by lattice self-diffusion. The stress exponent n ≡ n1 = δ In ∊/δ In σ is a function of both stress and temperature. Generally, n1 decreases, reaches a minimum and increases again with the increasing stress. The lowest value of n1 ≃ 5·4. Non-conservative motion of jogs on screw dislocations dependent on lattice self-diffusion was suggested to be a rate-controlling process in Region 1.In the region of higher creep rates-Region 2-the apparent activation energy Qc2, is considerably higher than the activation enthalpy of lattice self-diffusion. The results for Region 2 have not been correlated with any of the known dislocation mechanisms.