Formation of multilayered scale during the oxidation of NiAl-Mo alloy

We have studied the oxidation behavior of a hypereutectic NiAl-Mo alloy. This alloy showed an initial rapid mass loss followed by a relatively steady state behavior. The oxide scale formed during the oxidation process was seen to have a multilayered structure comprising of NiO, NiAl2O4, NiMoO4 and Al2O3 with minor amounts of MoO2 in the sub-scale region. The oxidation behavior is influenced significantly by the formation and stability of the constituent oxides, especially NiMoO4. Hence the decomposition behavior of NiMoO4 in the 1100-1200 °C was studied as well. The thermal decomposition of the NiMoO4 was slow at 1100 °C, but accelerated at 1200 °C, resulting in the formation of NiO, which remained in the oxide scale, and MoO3, which volatilized away.