Microstructural and oxidation study of chromia forming Molybdenum-Tungsten based alloys
Résumé
Many industrial applications require high-performance materials with good mechanical properties and high resistance to oxidation/corrosion at high temperatures. This is especially true in the glass industry, where metallic or ceramic materials suffer from high temperature oxidation and corrosion by molten glass at temperatures as high as 1200°C or more. In this case, iron, or nickel based alloys cannot be used, due to their drastic loss of mechanical properties above 1200°C. Considering high temperature mechanical properties and corrosion resistance to molten glass, development of refractory alloys based on tungsten and/or molybdenum could be judicious. Oxidation resistance of these metals being very bad, they have to be alloyed with elements which form stoichiometric, protective oxide layers. Among the elements which can be used for this purpose, chromium is preferred since chromia has a low solubility in most glasses.
The microstructure and the oxidation behaviour of CrMoW alloys have been nvestigated over a wide range of composition. The sintering mechanism with palladium is based on the presence of a liquid CrPd phase at the grain boundaries, which allows a rapid diffusion of the elements. Excellent oxidation behaviours are observed for alloys with a high chromium and tungsten contents. Acomparison of the calculated parabolic rates
constant for the alumina and chromia alloys shows that such chromia forming alloys can have an oxidation resistance similar to that of alumina forming alloys at high temperatures.
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