Al对Fe-20Cr-35Ni-0.6Nb合金显微组织和抗氧化性的影响

采用增量法研究了不同Al含量(0.5%、1.5%、2.5%,质量分数)的Fe-20Cr-35Ni-0.6Nb含Nb合金在1000 ℃空气条件下的抗氧化。采用SEM、EDS、TEM、拉曼光谱等手段研究了合金的显微组织和氧化膜特性。结果表明,3种含Nb合金组织为单相奥氏体,基体中存在少量弥散分布的NbC沉淀相,氧化前后沉淀相含量和晶粒大小保持不变。添加0.5%和1.5%的Al后,含Nb合金的表面形成多层结构的氧化膜,最外层和第三层为Cr₂O₃,次表层主要为NiCr₂O₄、NiFe₂O₄和Fe₂O₃,最内层为Al₂O₃内氧化层。基体中的NbC析出相和氧化膜中少量Nb的氧化物(Nb₂O₅)加剧了氧化膜的疏松。当Al含量增加到2.5%时,含Nb合金表面形成连续致密的Al₂O₃氧化膜,降低了Fe-20Cr-35Ni-0.6Nb合金的氧化速率,提高了抗氧化性。

Effect of Al on microstructure and oxidation resistance of Fe-20Cr-35Ni-0.6Nb alloy

Oxidation resistance behaviors of Fe-25Cr-35Ni-0.6Nb-xAl (x=0.5%, 1.5%, 2.5%, mass fraction) Nb-containing alloys at 1000 ℃ in air were investigated by mass gain method. The microstructure and oxide scales of the alloys were observed and analyzed by SEM, EDS, TEM and Raman spectroscopy. The results show that the microstructure of the three Nb-containing alloys is single-phase austenite, and a small amount of NbC precipitated phases are dispersed in the matrix. The content of precipitated phase and the grain size remain unchanged before and after oxidation. With the addition of 0.5% and 1.5% Al, a multilayer oxide film forms on the surface of the Nb-containing alloys, of which the first and third layers are Cr₂O₃, the subsurface layer is mainly composed of NiCr₂O₄, NiFe₂O₄ and Fe₂O₃, and the innermost layer is Al₂O₃ internal oxide. In addition, the porosity of the oxide film is aggravated by NbC precipitates in the matrix and a small amount of Nb oxides (Nb₂O₅) in the oxide film. When the Al content increases to 2.5%, a continuous and dense Al₂O₃ oxide film forms on the surface of Fe-25Cr-35Ni-0.6Nb alloy, which reduces the oxidation rate and improves the oxidation resistance of the alloy.