电沉积结合包埋渗制备复合涂层的高温氧化行为

High Temperature Oxidation Behavior of Composite Coatings Prepared by Electrodeposition Combined with Pack Cementation

摘要:

为了提高铌合金的高温抗氧化性能，首先采用阴极匀速旋转电沉积法在铌合金表面制备了钼层，然后通过包埋渗硅获得硅化物复合涂层。研究了沉积态钼层和硅化物涂层的形成和微观组织结构，对比分析了有或无涂层C103合金的高温氧化行为。结果表明，阴极匀速旋转法使沉积的电流效率提高一倍多，钼层呈胞状结构、以非晶形式存在。经包埋渗硅后，生成了表层以MoSi2为主、中间层为NbSi2的复合涂层，涂层与基体结合良好。经1200 ℃氧化后，涂层试样的氧化抛物线速率常数分别为1.83×10-2 mg2cm-4h-1、8.08 mg2cm-4h-1，与之相比，裸合金的氧化抛物线速率常数则为5.87×103 mg2cm-4h-1，而且仅氧化10 h裸合金即出现了严重粉化；在高温氧化过程中，复合涂层表面生成SiO2垢层，具有优良的抗高温氧化性能。

Abstract:

In order to improve the high temperature oxidation resistance of niobium alloy, a molybdenum layer was firstly prepared on the surface of niobium alloy by electrodeposition method with uniform rotating cathode, and then the silicide composite coatings were obtained by the halide activated pack siliconizing. The formation and microstructure of as-deposited molybdenum layer and silicide coating were studied, and the high temperature oxidation behavior of C103 alloy with or without coating was compared and analyzed. The results showed that the current efficiency during electrodeposition was twice as high as that by conventional electrodeposition. The prepared molybdenum layer was amorphous with a cellular structure. After pack siliconizing, mainly MoSi2 and NbSi2 predominated the surface layer and intermediate layer of the composite coatings, respectively, and the composite coatings exhibited a strong interfacial bonding to the substrate. Thermally exposed to 1200 °C, the coated samples showed parabolic rate constants of 1.83×10-2 mg2cm-4h-1 and 8.08 mg2cm-4h-1, respectively. By comparison, a higher parabolic rate constant about 5.87×103 mg2cm-4h-1 was detected in the bare alloy, and pesting oxidation was found in the bare alloy only 10 h exposure. The composite coatings present excellent resistance to high temperature oxidation due to the formation of SiO2 surface scales during thermal exposure.