γ-TiAl合金在高温熔盐环境下的腐蚀机理

Corrosion mechanism of γ-TiAl alloy at high temperature in molten salt environment

在800℃、75%Na2SO4和25%NaCl的熔融盐环境中,对名义成分为Ti-48Al-2Cr-2Nb的γ-TiAl合金进行高温腐蚀实验。通过氧化动力学分析、扫描电镜观察及X射线衍射分析,研究全片层γ-TiAl合金的氧化腐蚀行为,以及高温腐蚀性环境对合金内部微观组织的选择性腐蚀机理。结果表明:在高温熔融盐腐蚀环境下,γ-TiAl合金主要形成由TiO2和Al2O3组成的氧化膜层,且高温熔融盐环境对合金内部微观组织存在明显的选择性腐蚀,即腐蚀路径沿α2与γ两相界面进入合金内部,并优先腐蚀α2相片层及γ相片层中的某些亚结构。合金片层组织中α2相与γ相间的抗氧化性能差异,以及熔融盐腐蚀性环境参与氧化中间反应并加速合金氧化过程是发生选择性腐蚀的主要原因。

The high temperature corrosion tests of Ti-48Al-2Cr-2Nb γ-TiAl alloy were carried out with salt mixture of 75% Na2SO4 and 25% NaCl（mass fraction） at 800 ℃.The high temperature corrosion behavior of the alloy and the selective corrosion mechanism of microstructure were also discussed,via oxidation kinetics analysis,scanning electron microscope observation and X-ray diffraction analysis.The results show that the oxide layer mainly composed of TiO2 and Al2O3 is formed during high temperature corrosion.The corrosion path initiates at the lamellar interfaces,and α2 phases as well as some substructures in γ phase have priorities of corrosion in molten salt environment,which proves the existence of the selective corrosion of lamellar structure.The difference in oxidation resistance between the two phases and the participation of molten salts in intermediate reaction,which accelerates the oxidation process,are considered as the main reasons of selective corrosion of microstructure in the alloy.