低膨胀IN909合金650℃的氧化行为

IN909低膨胀高温合金具有较低的热膨胀系数和高的综合力学性能，但由于合金不含Cr，其抗氧化性能较差，因此，在高温使用时需采用氧化涂层.为进一步提高合金的抗氧化性能，采用扫描电镜（SEM）和能谱分析（EDX）方法，研究了低膨胀IN909合金在650℃的氧化行为，结果显示IN909合金的氧化质量增加分段遵循抛物线规律，氧化由晶界开始，形成Nb、Ti、Si等元素的晶界氧化物；Fe置换氧化物中的Nb、Ti、Si，形成外层Fe的氧化物.氧化过程中，Fe由基体向合金表面扩散，Nb和Ti由氧化过渡层向基体扩散.Nb和Ti在基体前沿的富集形成ε相大量析出的薄层，可有效地阻碍Fe元素的进一步扩散，降低氧化速率.

Oxidation behavior of low thermal expansion superalloy IN909 at 650℃

The low thermal expansion superalloy IN909 has high comprehensive mechanical properties and lower thermal expansion coefficient. Because no Cr is added, the alloy exhibits worse oxidation resistance. Thus, the coating needs to be applied if the alloy services at high temperature. In order to improve further the oxidation resistance, the oxidation behavior of low thermal expansion alloy IN909 at 650℃ was studied using scanning electron microscope （SME） equipped with energy dispersive spectrometry （EDX）. The results indicate that the oxidation kinetics obeys the different parabolic law in different duration. The oxidation initiates from grain boundaries, forming the oxides of Nb, Ti and Si. Then, Fe replaces Nb, Ti and Si in the oxides, forming the oxides of Fe at the outside layer. In the oxidation process, Fe diffuses from the matrix to the surface, while Nb and Ti diffuse from the transition layer towards the matrix. The concentration of Nb and Ti at the front of matrix causes the considerable precipitation of ε phase, which can efficiently resist the diffusion of Fe and hence decrease the oxidation rate.