Oxidation Behavior of Fe-36% Ni Invar Alloy Coarse Columnar Crystals at High Temperature

The oxidation behavior of Fe-36%Ni invar alloy coarse columnar crystals at 1000 ℃ and 1100 ℃ for different time was investigated by constant temperature oxidation weight gain method. By using laser confocal microscope（LSCM）,scanning electron microscopy（SEM） and X-ray diffraction（XRD）, the oxide layer structure, element distribution and phase composition of the oxide layer were analyzed. The results show that the oxidation kinetics curves of invar alloy at 1000 ℃ and 1100 ℃ conform to parabola law. The oxide layer structure of the alloy at 1000 ℃ and 1100 ℃ is divided into three parts,external scale, intragranular scale and intergranular scale. The external scale is mainly composed of Fe element and O element.The content of Fe element in the intragranular scale is lower than that in the matrix, while the content of Ni element is higher.Oxygen element is enriched in island area, while Ni element is enriched in other places. The external scale at 1100 ℃ is divided into three parts, the outer layer is Fe₂O₃. The oxidation weight gain and the thickness of oxide layer of invar alloy oxidized at 1100 ℃ for 1h exceed that oxidized at 1000 ℃ for 5 h, so it is necessary to formulate a reasonable heating system.