Effect of Manganese Addition on Reactive Evaporation of Chromium in Ni-Cr Alloys

Chromium is used as an alloy addition in stainless steels and nickel-chromium alloys to form protective chromium oxide scales. Chromium oxide undergoes reactive evaporation in high-temperature exposures in the presence of oxygen and/or water vapor. Deposition of gaseous chromium species onto solid oxide fuel-cell electrodes can reduce the efficiency of the fuel cell. Manganese additions to the alloy can reduce the activity of chromium in the oxide, either from solid solution replacement of chromium with manganese (at low levels of manganese) or from the formation of manganese-chromium spinels (at high levels of manganese). This reduction in chromium activity leads to a predicted reduction in chromium evaporation factors as much as 35 at 800 °C and 55 at 700 °C. Quantifying the effects of manganese additions on chromium evaporation should aid alloy development of metallic interconnects and balance-of-plant alloys.