不同镍基粉末高温合金的氧化行为研究

Oxidation Behavior of Different Powder Metallurgy Nickel Based Superalloys

摘要:

对FGH4113A(WZ-A3)、FGH96和FGH97三种镍基粉末高温合金进行815、900和1000℃大气环境下的高温氧化试验。采用静态增重法测定合金在不同温度下的氧化动力学曲线并评估其抗氧化能，利用X射线衍射、扫描电子显微镜、能谱仪等分析合金氧化后的表面及截面形貌、成分及结构等。结果表明：815和900℃时三种合金均为完全抗氧化级，1000℃时WZ-A3为抗氧化级，FGH96为次抗氧化级，FGH97仍为完全抗氧化级。WZ-A3和FGH96合金经1000℃高温氧化后氧化层结构类似，最外层为TiO2，中间层为Cr2O3+少量TiO2的混合层，最内层为树枝状Al2O3；WZ-A3合金氧化中间层和最内层的分界处还存在Nb和Mo元素的富集。三种合金氧化性能的差别与Al含量有关。FGH97中Al含量较高，经1000℃氧化后，外表面存在孤岛状TiO2，在表面形成致密的Al2O3层，有效阻隔了其他合金元素向外扩散，使合金表现出优异的抗氧化性。WZ-A3和FGH96中Al含量较低，形成的树枝状Al2O3层无法有效形成隔离保护，形成的Cr2O3氧化层在高温下挥发形成孔洞破坏了氧化层的致密度。1.0wt% Ta和 1.2wt%Nb的添加一定程度提高了WZ-A3合金的抗氧化性。

Abstract:

Three nickel-based powder superalloys FGH4113A (WZ-A3), FGH96 and FGH97 were subjected to oxidation tests in air at 815, 900 and 1000℃. Static weight gain method was used to determine the oxidation dynamics curve of the alloys at different temperatures and to evaluate the oxidation resistance. The surface and cross-sectional morphology, composition and structure of specimens were analyzed after oxidation tests by X-ray diffraction, scanning electron microscopy, energy spectrometer. The results showed that the three alloys were completely antioxidant grade at 815 and 900℃, WZ-A3, FGH96 and FGH97 were antioxidant grade, secondary antioxidant grade and complete antioxidant grade respectively at 1000℃.The oxide layers of WZ-A3 and FGH96 alloys were similar after oxidation at a high temperature of 1000℃, which consisted of an outermost layer TiO2, a middle layer mixed layer of Cr2O3 and a small amount of TiO2, an innermost layer was dendritic Al2O3. There was 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 was related to Al content. Al content was low in WZ-A3 and FGH96 and the dendritic Al2O3 layer formed can’t effectively form isolation. After the Cr2O3 reaction, it evaporated to form holes, which destroys the density of the oxide layer at high temperatures. Al content in FGH97 was high such that the formation of a dense Al2O3 layer on the surface can effectively block the outward diffusion of other alloying elements after oxidation at 1000℃, so the FGH97 exhibited excellent oxidation resistance. The addition of 1.0wt%Ta and 1.2wt%Nb has improved the oxidation resistance of WZ-A3 alloy to a certain extent.