A TEM study of sulfur distribution in oxidized Ni40Al and its effect on oxide growth and adherence

During oxidation at 1100 °C of a normal purity and a S-doped Ni-40at%Al alloys, the sulfur distribution in the alloy, in the scale and at the scale/alloy interface was studied, as well as its influence on scale growth. S-doped NiAl, sulfur was found incorporated in the growing alumina scale in the form of NiS tiny precipitates as well as segregated at the alumina/alloy interface. This showed that the oxide/alloy interface is not an unlimited sink for S and that excess sulfur can pass through the interface and precipitate into the growing scale. cs results showed no effect of sulfur on scale development, except a significant decrease in alumina adhesion associated to enhanced pore formation for the S-doped alloy.