The Initial Oxide Scale Development on a Model FeNiCrAl Alloy at 900 degrees C in Dry and Humid Atmosphere: A Detailed Investigation

Artikel i vetenskaplig tidskrift, 2014

The investigated alumina forming FeNiCrAl model alloy shows protective oxidation behavior in dry and humid environment at 900 A degrees C. Hence, this type of alloy may replace conventional chromia forming austenitic alloys in aggressive oxidizing/reducing environments. A detailed investigation of the oxide scale development reveals a complex initial scale development. Firstly, at alloy grain boundaries, a thin Al rich oxide forms which is replaced by transient alumina platelets in dry and equiaxed alpha-Al2O3 crystallites in humid atmosphere. The scale at alloy grain centers develops via a layered scale of external chromia:Fe/Ni metal inclusions:internal alumina to a layered external spinel:internal alumina scale in dry atmosphere. In humid condition an additional oxide feature appears on the center of large alloy grains i.e. thick oxide protrusions. Despite the initially different phase compositions a continuous protective alpha-Al2O3 scale forms both atmospheres.