Oxidation Behavior of Different Powder Metallurgy Nickel-Based Superalloys

Three nickel-based powder superalloys FGH4113A (WZ-A3), FGH96 and FGH97 were subjected to oxidation tests in air at 815, 900 and 1000 degrees C. The oxidation dynamics curve of the alloys at different temperatures was determined by static mass gain method and the oxidation resistance was evaluated. The surface and cross-sectional morphology, composition and structure of specimens were analyzed by XRD, SEM, EDS after oxidation tests. The results show that three alloys are completely antioxidant grade at 815 and 900 degrees C. WZ-A3, FGH96 and FGH97 are antioxidant grade, secondary antioxidant grade and complete antioxidant grade, respectively at 1000 degrees C. The oxide layers of WZ-A3 and FGH96 alloys are similar after oxidation at high temperature of 1000 degrees C, which consist of an outermost layer TiO2, a middle mixed layer of Cr2O3 and a small amount of TiO2 and an innermost layer of dendritic Al2O3. There is the enrichment of Nb and Mo elements at the boundary between the middle and the innermost layer for WZ-A3. The difference in oxidation properties of the three alloys is related to Al content. Al content in FGH97 is high, and the formation of a dense Al(2)O(3 )layer on the surface can effectively block the outward diffusion of other alloying elements after oxidation at 1000 degrees C, so the FGH97 exhibits excellent oxidation resistance. Al content is low in WZ-A3 and FGH96 and the dendritic Al(2)O(3 )layer formed can not effectively form isolation. After the Cr2O3 reaction, it evaporates to form holes, which destroys the density of the oxide layer at high temperature. The additions of 1.0wt%Ta and 1.2wt%Nb can improve the oxidation resistance of WZ-A3 alloy to a certain extent.