| The long-term oxidation behavior of commercial wrought Fe- and Ni-base alloys was studied, with particular focus on the oxidative effects of alloying elements, especially minor elements, such as Si. The behavior of oxide scale growth, scale spallation, subsurface changes, and chromium interdiffusion in the alloy were analyzed in detail. A numerical model is presented that predicts the service life-time of chromia-forming alloys during cyclic oxidation by simulating oxidation kinetics and chromium interdiffusion in the alloy subsurface. The results show good agreement with measured depletion profiles if proper parameters are used, particularly the Cr interdiffusion coefficient.; The cyclic oxidation kinetics of Fe-based alloys was generally found to show poorer oxidation resistance than Ni-based alloys. All Fe-based alloys showed a large amount of spallation, even to breakdown, during cyclic oxidation at 1000°C. The Ni-base alloys also showed dramatic variability in their cyclic oxidation behavior, from negative weight change (large spallation) to stable positive weight gain (small spallation).; Increasing the Si content in the Fe-based alloys (<1 wt.%) resulted in improved oxidation resistance. Formation of Si-rich oxide particles at the alloy/scale interface was inferred to aid cyclic oxidation resistance by impeding the diffusion of oxygen and chromium, thus decreasing oxidation kinetics. A higher silicon content facilitated the formation of oxide protrusions at the alloy/scale interface of the Ti-containing alloys, which can result in larger stresses and greater spallation. Si addition to Ni-based alloys showed the effects on increasing the chromium diffusivity and decreasing the oxide growth rate. Both of these factors beneficially contributed to the cyclic oxidation resistance of the alloy. |
