NiCr涂层结构对Nb-1Zr合金抗氧化性能的影响

Effects of Ni Cr Coating Microstructure on Oxidation Resistance of Nb-1Zr Alloys

为提高Nb-1Zr合金基体在600℃大气环境下的抗氧化性能,采用等离子增强电弧离子镀技术在Nb-1Zr合金表面低于300℃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 h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Nb_2O_5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Cr_2O_3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Cr_2O_3层,双层致密氧化膜的形成确保了基体抗氧化性能的提高。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 h,氧化增重率仅有0.08g·(m^2·h)^(-1)。

In order to improve the oxidation resistance of Nb-1Zr alloys in 600 °C atmospere, a series of NiCr coatings with different composite structure were deposited on Nb-1Zr alloys by plasma enhanced ion plating below 300 °C. Oxidation resistance property of the NiCr coating was studied by isothermal oxidation. The mechanism of invalidation and oxidation resistance of NiCr coating with different microstructure was revealed. The results show that a channel for oxygen diffusion can be formed by the micro holes communicating with each other in the single layer NiCr. So the Nb-1Zr matrix near the interface is oxidized firstly and Nb_2O_5 based oxide powder is generated which is gradually increased in amount along with the oxidation time, causing the breakage of coating. The ＂through holes＂ can be significantly reduced by NiCr multilayer composite structure, but the failure mode of the coating is not changed. By introducing the Cr interlayer, the diffusion of oxygen would easily be absorbed and a dense Cr_2O_3 layer is formed which can discourage the further diffusion of oxygen into the Nb matrix. In addition, a dense Cr_2O_3 layer is also formed on the surface of Cr/NiCr multilayer coating by diffusion of Cr. As a result, the oxidation resistance of the Nb-1Zr alloy can be improved. After oxidizing at 600 °C for 500 h, the mass gain rate of Nb-1Zr alloy with Cr/NiCr multilayer composite coating is only about 0.08 g·（m^2·h）^（-1）.