Abstract
Several nickel alloys containing high chromium contents, and other elements known to enhance resistance to metal dusting, were tested in a flowing gas mixture of 68% CO + 26% H2 + 6% H2O at 6800C, corresponding to aC = 2.9. The onset of dusting was accelerated by using temperature cycling conditions, to shorten the life of otherwise protective oxide scales. The total duration of the test was 1,200 cycles, each of 45 min at temperature, and 15 min cooling. All test alloys developed chromia scales, but dusted to some extent, developing filamentary carbon deposits decorated with metal nanoparticles. Different numbers of cycles were required to initiate coking and surface damage, and alloys were compared based on the time to initiate dusting reaction. A shallow alloy subsurface zone of very fine carbide precipitates formed, and surface pitting commenced. Differences in behavior between the alloys are discussed in terms of alloy composition.
