Page 96 - 《摩擦学学报》2021年第6期

第 6 期 李正阳, 等: 工作电压对N36锆合金表面微弧氧化涂层磨蚀性能的影响 881

behavior of MAO coating on Zr alloy was analyzed by fretting wear test rig combined with an electrochemical
workstation. The test solution was 1 200 mg/L H 3 BO 3 and 2.2 mg/L LiOH. The fretting parameters were selected as the
displacement amplitude of 100 μm, the load of 20 N, and the frequency of 5 Hz. The test time was 2 000 s for 10 000
cycles. Before the fretting corrosion test, the sample was immersed for 500 s to obtain a stable electrochemical state. The
results showed that the surface morphology of MAO coating presented typical porous and volcanic melting
characteristics. With the increase of voltage, the volcanic melting gradually extruded and the size of pores in coating
surface increased. The MAO coating was mainly composed of Zr, m-ZrO 2 , and t-ZrO 2 , and the high-temperature phase
of t-ZrO 2 existed in coating, indicating that high stress in coating stabilized the phase of t-ZrO 2 . The MAO coating
presented a higher roughness and hardness than substrate, and MAO coating with 260 V had the highest roughness value
of 1.36 μm. The increase of hardness in coating was caused by the high hardness of ZrO 2 ceramics. MAO coating can be
divided into the inner dense layer and outer porous layer according to the cross-section morphology and EDS line-scan
results. The oxide layer had a very obvious distinction from substrate, and no cracks and defects at the interface between
coating and substrate were observed. The corrosion resistance and fretting wear resistance of MAO coating were
determined by the density of inner layer and the bonding strength with substrate. The thickness of MAO coating
increased with the increase of working voltage, and the thickness was about 5~9 μm. The MAO coating with 260 V had
the highest bonding strength of 44.3 N. Because MAO coating generated more cracks and defects under high working
voltage, resulting in the decrease of bonding strength. Compared with the substrate, MAO coating had better corrosion
resistance, and the MAO coating with 260 V had a highest corrosion potential (−0.205 V) and lowest corrosion current
−9 2
density (6.24×10 A/cm ). Because the MAO coating with 260 V had the densest structure, and the inner dense layer
prevented the corrosion solution from entering into the surface of substrate. The electrochemical impedance
spectroscopy results indicated that the arc radius of MAO coating was larger than that of Zr alloy substrate. According to
the phase angle, three time constants were observed. The high frequency regions were corresponding to the properties of
solution, and the medium frequency regions was belonging to the outer porous layer, while the low frequency regions
represented the inner dense layer. Open circuit potential (OCP) dropped sharply to a lower value when the fretting test
began. Because the mechanical wear destroyed the stable electrochemical state of coating. With the progress of fretting
test, the formation rate and removal rate of passivation film reached a new dynamic balance. As a result, OCP values for
all MAO coatings began to stabilize. After the initial rapid rose, the friction coefficient value quickly reached a stable
state. MAO coating with 340 V had the highest friction coefficient value. All the MAO coatings showed obvious furrow
traces on the wear surface, and many wear debris with different sizes were non-uniform distributed on the wear surface.
The main wear mechanism of MAO coating was abrasive wear and oxidation wear. The 3D profiles of all the wear scar
showed obvious cave and the wear damage of Zr alloy was the largest. The wear damage of MAO coating was relatively
slight, and the wear depth was shallow, indicating that MAO coating can significantly improve the wear resistance of Zr
5 3
alloy. The wear rate of Zr alloy was 2.14×10 μm /(Nm), and the wear rate of MAO coating with 260 V was only 1 / 4 of
that Zr alloy substrate.
Key words: zirconium alloy; micro-arc oxidation; fretting corrosion; wear mechanism; corrosion

锆(Zr)合金由于较好的耐腐蚀性能、机械性能、耐 面原位生成氧化物陶瓷涂层的技术，可以显著地提升
中子辐射性能和热中子吸收截面低等优点广泛用于 材料的耐腐蚀和磨损性能. Cheng等 [5-6] 发现Zirlo合金
[1]
压水堆燃料组件包壳材料 . 在反应堆运行时，燃料包 和Zr-2合金表面生成的MAO涂层主要由单斜m-ZrO 2
壳处于高温、高压、高流速和强辐射的环境中，其服役 和四方t-ZrO 组成，在高浓度的铝酸盐电解液体系下
2
[7]
环境极其苛刻. 当高速流动的冷却剂经过燃料包壳 形成的涂层具有更好的耐磨性. Xue等 发现Zirlo合金
时，会导致其受到横向流和轴向流的作用，从而诱发 表面MAO涂层的磨损率仅为基体的1/60. MAO涂层
流致振动. 流致振动会使定位格架和燃料包壳间发生 的主要磨损机理为粘着磨损，而Zirlo合金的磨损机理
[8]
相对运动，造成接触部位的磨蚀，严重事故情况下会 为磨粒磨损. Guo等 在高温高压水化学环境下分析
引起包壳管破损 [2-3] . 目前，支撑格架与燃料包壳之间 了Zirlo合金表面MAO涂层的微动磨损性能，发现MAO
[4]
的磨蚀是造成压水堆燃料失效的最主要原因 . 涂层能减少氧化和腐蚀，从而降低磨损量. 目前，针对
微弧氧化(MAO)是一种能在阀金属及其合金表 我国自主研发N36 Zr合金的MAO涂层研究较少，缺乏