High-temperature alloys from VDM Metals are characterized by their specific resistance to the attack of hot gases and combustion products above 550 ℃. This specific resistance requires the formation of protective oxide layers on the surface. Of the three elements aluminium, silicon and chromium which can be used for the formation of the protective oxide layers, chromium can be used most universally. However, aluminium has to be used for service temperatures in oxidizing atmospheres above 1,000 ℃.
The addition of small amounts of yttrium and of rare earth elements increases the adhesive strength of the protective oxide layer. Addition of silicon is effective, mainly in the initial stages of oxidation, as it contributes to a very rapid oxide film formation. Increasing nickel content produces increasing resistance to uniformly carburizing gases but has a more detrimental effect with regard to resistance to sulfur bearing media.