NiCr涂层结构对Nb-1Zr合金抗氧化性能的影响

Effects of NiCr coatings’ microstructure on oxidation resistance of Nb-1Zr alloys

摘要:

为提高Nb-1Zr合金基体在600℃大气环境下的抗氧化性能,本文采用等离子增强电弧离子镀技术在Nb-1Zr合金表面低于300℃条件下实现不同复合结构的NiCr涂层。利用恒温氧化表征了涂层在600℃、500小时大气环境下的抗氧化性能,揭示了不同复合结构涂层失效以及抗氧化机理。结果表明,单一NiCr涂层中存在的大量“微孔“结构缺陷相互连通构成了氧元素进入基体的扩散通道,界面处基体首先发生氧化,生成以Nb2O5为主的粉末状氧化产物。随着氧化时间的延长,氧化产物逐渐增多,体积逐渐膨胀,造成表面鼓泡直至破裂失效。采用NiCr多层复合结构能够显著降低涂层中形成“贯穿孔“的几率,但并未改变涂层的失效方式。而基体与NiCr层之间引入Cr过渡层,能够在界面处与扩散进入的氧首先反应生成致密的Cr2O3层,阻碍氧向基体的进一步扩散,且随着氧化时间的延长,涂层中的Cr向表面的扩散使得其表面相应形成一层致密的Cr2O3层,双层致密氧化膜的形成确保了基体抗氧化性能的提高。研究结果显示,Cr/NiCr多层复合结构涂层能够使Nb-1Zr合金在600℃大气环境下的抗氧化时间延长至500小时,氧化增重率仅有0.08 g/m2.h。

Abstract:

In order to improve the Nb-1Zr alloys’ oxidation resistance, a series of NiCr coatings with different composite structure were deposited on Nb-1Zr alloys by Plasma enhanced ion plating bellow 300℃. By means of isothermal oxidation, NiCr coatings’ oxidation resistance property was studied in detail. The mechanism of invalidation and oxidation resistance of NiCr coating with different microstructure was revealed. The results showed that a channel for oxygen diffusion could be formed by the micro holes communicating with each other in the single layer NiCr. So the Nb-1Zr matrix near the interface would be oxidized firstly and Nb₂O₅ based oxide powder was generated which gradually was increased along with the oxidation time, causing the breakage of coating. That “through holes” can be significantly reduced by NiCr multilayer composite structure, but the coatings’ failure mode was not changed. By introducing the Cr interlayer, the diffusion of oxygen would easily be absorbed and a dense Cr₂O₃ layer was formed which can discourage the further diffusion of oxygen into the Nb matrix. And also a dense Cr₂O₃ layer could also be formed on the surface of Cr/NiCr multilayer coating by diffusion of Cr. As a result, the Nb-1Zr alloy’s oxidation resistance could be improved. After oxidizing at 600℃ for 500 hours, The weight gain rate of Nb-1Zr alloy with Cr/NiCr multilayer composite coating was only about 0.08 g/m₂.h.