C. Geers, M. Schütze
The stability of high temperature materials in reducing highly carbonaceous atmospheres in the temperature range of 400 to 800°C can be raised with the help of a nickel-tin coating. Coking and metal dusting are dependent on the catalytic activation of the carbonaceous gas species by the material surface components iron, cobalt and/or nickel. If the access to the catalytic active metal centers is impeded for the gas species, the primary condition for the metal dusting attack — atomic carbon — is not available. The dissociation of e.g. carbon monoxide is suppressed on nickel-tin surfaces. Initial tests with a nickel-tin coating on low alloy steel have shown an improved behavior under metal dusting conditions up to at least 3000 hrs. Following these initial tests the coating was applied to several conventional materials including low alloy steel, ferritic and austenitic high alloy steel and nickel base alloys. Test coupons were exposed under metal dusting conditions at 620°C for several hundred hours and evaluated via metallographic and microprobe analyses. Alloy parameters influencing the effectiveness and resistance of the coating were identified.