Influence of water vapour in air and of TaC carbides in alloy on the high temperature oxidation of cobalt-based refractory alloys. Part 2: Results in oxidation in wet air

摘要

Besides nitrogen and oxygen other gaseous species (CO, CO_2, SO_2, H_2O...) are generally present in the hot atmosphere in which refractory alloys are in service, and their presence influences the behaviour of alloys in high temperature oxidation, often in the wrong direction, i.e. with rather detrimental effect. Notably, it is widely recognized that water vapour plays an important role, but not necessarily unfavourable for the sustainability of the metallic component. If it is true that the presence of water vapour in air tends to provoke the volatilization of SiO_2 and AI_2O_3 protecting the silica or alumina-forming alloys, and to accelerate of Cr_2O_3 covering the chromia-forming ones, some advantages were also noticed: sometimes a slowdown in speed for the oxidation rate and frequently an improvement of the scale adherence when temperature varies.