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Abstract
The influence of oxidation on the creep behaviour of high-purity iron at 823–1283 K at constant tensile stresses of 4–16 MN m−2 has been studied with a specially constructed ultra-high-vacuum unit. Steady-state creep was enhanced (oxidation-weakening) as the oxygen pressure was increased from 10−9 to 1 mbar. Oxidation-assisted vacancy injection is believed to enhance dislocation and point-defect mobility, especially if the adhering oxide film is repeatedly fractured and repaired during substrate creep. Oxidation-strengthening appears most likely at very low oxygen pressures where a strong, adherent film can impose a mechanical constraint to substrate creep and may provide a barrier to emergent dislocations. Oxidation was found to enhance the temperature effect on steady-state creep irrespective of the creep deformation mechanism in operation.