High Temperature Oxidation Behavior of FGH4096 Superalloy Prepared by Electron Beam Refining

The FGH4096 alloy with an oxygen impurity mass fraction of only 0.000 9% was prepared by electron beam refining, and was subjected to constant temperature oxidation tests at 750 ℃ and 900 ℃ for 100 h. The surface morphology, cross-section structure, and phase composition of the oxide film were investigated, and the high temperature oxidization behavior of the alloy was analyzed and compared with that of the FGH4096 alloy with an oxygen impurity mass fraction of 0.001 6% prepared by vacuum induction melting. The results show that compared with those of the alloy prepared by vacuum induction melting, the increment of oxidizing mass per unit area and the thickness of oxide film of the FGH4096 alloy prepared by electron beam refining after high temperature oxidation under the same conditions were smaller, and the average oxidation rates at the oxidizing temperatures of 750, 900 ℃ were both less than 0.1 g·m⁻²·h⁻¹; the alloy was complete oxidation resistant. After oxidation at 900 ℃ for 100 h, the oxide film of the alloy consisted of TiO₂ and Co(Ni)Cr₂O₄ in the outermost layer, Cr₂O₃ in the middle layer and Al₂O₃ in the inner layer. Compared with those of the alloy prepared by vacuum induction melting, the oxide film of the alloy prepared by electron beam refining was thinner with less porous and better uniformity and densification, and the alloy had lighter degree of internal oxidation. At the initial stage of oxidation, TiO₂ and Cr₂O₃ were formed on the surface of the alloy. With the extension of oxidation time, Co(Ni)O generated in the outer layer reacted with Cr₂O₃ to form Co(Ni)Cr₂O₄ spinel phase; the oxide film was gradually dense, and a large amount of Al₂O₃ was formed in the inner layer at low oxygen partial pressure. The content of oxygen impurities in the alloy by electron beam refining was relatively low, the number of defects was relatively few, which effectively reduced the growth rate of n-type semiconductor oxide Al₂O₃ along the grain boundaries, resulting in the relatively small oxide film thickness.