Influence of sample thickness and microstructure on metal dusting behavior of NiCrFeAl alloys

Samples of alloy 601, 602 CA and 602 MCA with different thickness and microstructure, all 600 grit laboratory ground, are compared. All samples are exposed to up to 5693 h at 600°C in a metal dusting producing atmosphere with a total pressure of 20 bar. A smaller sample thickness leads to an increased pit density for alloy 601 and an increased pit density, a longer incubation time and an increased pit depth growth rate for alloy 602 CA. This is attributed to lower stresses in the scale of the thinner samples. Grain size effects of the substrate are probably concealed by the deformed and recrystallized subsurface due to the 600 grit finish of the samples. If carbides are unavoidable in an alloy, they should be small, as they can serve as chromium suppliers during scale formation better than larger ones. They increase incubation time and pit depth growth rate.