锆表面微弧氧化膜1000~1200℃高温蒸汽氧化行为研究

High Temperature Oxidation Behavior of Pure Zr Coated by Microarc Oxidation in 1000~1200℃ Steam

目的研究微弧氧化表面处理对纯锆高温蒸汽氧化行为影响。方法采用微弧氧化技术(MAO)在磷酸盐电解液中纯锆表面制备厚约2.5μm的陶瓷膜,再利用热重分析仪(TGA)测量它们在1000~1200℃蒸汽环境中的氧化性能,并分析蒸汽氧化前后氧化膜的微观结构、物相组成。用辉光放电谱仪(GDOES)分析蒸汽氧化前后锆基体及微弧氧化样品Zr、O、P、Na、C、H元素的成分深度分布。结果锆基体及微弧氧化膜加速氧化动力学转变温度约为600℃。在1000℃蒸汽中,微弧氧化处理的纯锆样品氧化增重低于锆基体。蒸汽温度达到1100℃以上时,锆基体和微弧氧化膜的氧化增重曲线几乎重合。蒸汽氧化初期氧原子快速扩散至β-Zr中,当较厚α-Zr(O)层和ZrO_(2)层形成后,氧化速率主要取决于氧在α-Zr(O)层中的扩散速率,而且氧化锆层阻挡了氢扩散进入锆基体。高温蒸汽氧化后,纯锆表面氧化层主要由单斜氧化锆(M-ZrO_(2))相和少量的四方氧化锆(T-ZrO_(2))相组成。结论在1000℃以下,微弧氧化膜增强了锆基体的抗蒸汽氧化能力,但1100℃以上没有保护作用。

The work aimed to study the effect of microarc oxidation(MAO)surface treatment on the high temperature steam oxidation behavior of pure zirconium.The oxidation resistance of pure Zr with and without a MAO ceramic coating of about 2.5μm thick in 1000~1200℃steam environment was evaluated by a thermogravimetric analyzer(TGA).The microstructures and phase components of bare and MAO-coated Zr before and after steam oxidation were analyzed.Their composition depth profiles of Zr,O,P,Na,C,and H elements before and after steam oxidation test were carried out by glow discharge optical emission spectroscopy(GDOES).It was found that their kinetic transition temperature for accelerated oxidation was about 600℃in water vapor environment.The mass gain of MAO-coated pure Zr was lower than that of bare Zr after 3600 s steam oxidation at 1000℃,however,their oxidation kinetics curves almost overlapped at 1100℃and 1200℃.In the initial stage of steam oxidation,oxygen atoms diffused rapidly intoβ-Zr substrate.When the thickα-Zr(O)layer and ZrO_(2) layer were formed,the oxidation rate of bare and MAO-coated Zr was mainly governed by the oxygen diffusion rate inα-Zr(O)layer.Furthermore,the zirconia layer prevented from hydrogen pickup into Zr substrate.After high temperature steam oxidation,the oxide layers of both bare and MAO coated pure Zr consisted of monoclinic zirconia(M-ZrO_(2))and a little tetragonal zirconia(T-ZrO_(2))phases.The MAO coating enhanced the steam oxidation resistance of pure Zr below 1000℃,but not above 1100℃.