| 摘要: |
| 发动机贮箱长寿命服役是航天技术发展的必然要求，工业纯钛 TA2 是火箭发动机重要结构材料之一，然而该材料与液体推进剂的长期相容性机理仍缺乏深入的研究，难以满足推进剂贮箱长寿命评估的需要。针对典型液体推进剂单推-3（DT-3）， 采用电化学方法研究工业纯钛 TA2 在液体推进剂 DT-3 中的电化学腐蚀行为，应用扫描电镜（SEM）、光电子能谱（XPS）分析 TA2 表面钝化膜的结构特征。动电位极化曲线测试表明，TA2 在 DT-3 中自腐蚀电流密度为 58 nA / cm2 ，腐蚀速率约为 0.5 μm / a，点蚀电位为 2.15 V，耐点蚀能力强；具有两段钝化电位区，在点蚀电位下，肼和硝酸肼对 TA2 钝化膜的破裂溶解过程具有协同效应。交流阻抗谱测试表明，TA2 表面钝化膜具有很高的反应阻抗，抗均匀腐蚀性能良好，且随着阳极电位的升高，表面钝化反应机理一致。氧化膜 XPS 分析表明，较高钝化电位下形成的钝化膜更完善，形成的是外层为 TiO2，内层为 Ti2O3、TiO 的双层结构特征的钝化膜。获得的 TA2 在 DT-3 中的电化学腐蚀机理对贮箱寿命评估具有重要指导作用。 |
| 关键词: 液体推进剂 TA2 电化学腐蚀 极化 光电子能谱(XPS) 钝化膜 |
| DOI：10.11933/j.issn.1007?9289.20220409002 |
| 分类号:V511 |
| 基金项目: |
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| Corrosion-resistance Mechanism of Commercially Pure Titanium TA2 in Liquid Propellant DT-3 |
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TANG Zhanmei, GUO Wei, JIANG Rongpei, FANG Tao
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Aerospace Liquid Propellant Research Center, Beijing Institute of Aerospace Testing Technology,Beijing 100074 , China
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| Abstract: |
| Long service life of engine tanks is necessary for development of aerospace technology. Commercially pure titanium TA2 is an important structural material for rocket engines. However, there has been insufficient research on the mechanism of long-term compatibility of TA2 with liquid propellants, making it impossible to assess the service life of propellant tanks or similar structure materials. The electrochemical corrosion behavior of commercially pure titanium TA2 with typical liquid propellant DT-3 was studied through potentiodynamic polarization tests and the electrochemical impedance spectrum(EIS). The structure of the passive film on the surface of TA2 was characterized by scanning electron microscopy(SEM) and x-ray photoelectron spectroscopy(XPS). The results of potentiodynamic polarization tests showed that the corrosion current density of TA2 in DT-3 was approximately 58 nA/cm2 , which was converted to a corrosion rate of approximately 0.5 μm / a. There were two-stage potentials for passivation in the anodic area before the pitting potential of 2.15 V. The surface morphology of the sample after polarization curve testing was observed using SEM. When the principal components of hydrazine and hydrazine nitrate existed alone, the passive film did not rupture even if the electrode potential reached 4 V. However, considerable pitting corrosion occurred when they coexisted above 2.15 V. The SEM graphs showed that small pits rapidly developed and connected to form large circular pits. The EIS results showed that the passive film of TA2 had high electrochemical reaction impedance. With an increase in anode potential from -0.35 V to 2 V, the Nyquist diagram had only one capacitance arc, indicating that the corrosion process had only one dominant electrochemical reaction. The components and structure of TA2 oxide film in different oxidation conditions were characterized using the XPS Ar+ sputtering depth analysis method. The results showed that the thickness and structure of the oxide film were different from those of the lower potential in the two-stage potentials. The following conclusions can be drawn from this experimental study: (1) TA2 has a low self-corrosion current density, high electrochemical reaction impedance, and low annual corrosion rate in DT-3. It has good resistance to uniform corrosion in DT-3. (2) TA2 has a high pitting potential and a large difference between pitting potential and self-corrosion potential in DT-3, resulting in strong pitting resistance. When the electrode potential reaches the pitting potential, hydrazine and hydrazine nitrate have a synergistic effect on the dissolution process, causing the passive film to rupture, leading to local corrosion. Thus, with use of TA2 in liquid propellant DT-3, an excessive local potential difference must be prevented. (3) As the electrode potential increases, the passivation film thickens; however, the passivation mechanism of TA2 in DT-3 does not noticeably change. In the corrosion process, the valence state of titanium is oxidized from zero to two, three, and ultimately four. The electrode potential affects the structure of the passive film. The XPS analysis of the oxide film showed that a passive film formed under higher passivation potential became more perfect; the passive film eventually became a double-layer structure characterized by an outer layer of TiO2 and an inner layer of Ti2O3 and TiO. The evolution of the passivation film structure of TA2 in liquid propellant DT-3 plays a crucial role in the surface treatment of titanium alloys. |
| Key words: liquid propellant TA2 electrochemical corrosion polarization photoelectron spectroscopy(XPS) passive film |
