多孔钛基表面电沉积稀土复相Ti-Ni合金梯度镀层的基础研究

Regarding that the existence of poor surface wear resistance and solderability for Tianium and its alloys to strict the development of aerospace engines and submarine technology, so the objectives of this project are to study electroplating mechanisms of Ti-Ni alloy gradient nanocomposite deposits on the surface of porous Ti substrate in ionic liquids. This research focus on the effects of different hole edge for porous Ti surface on affecting electrical crystallization mechanisms, interfacial charge transfer between Ti cathode and ionic solution, and the relationship between complexing agent and reduction potential different of Ni2+, Ti3+ ions. According to the coupling effects of ultrasonic oscillations and double-pulsed current during electroplating process, textural growth and sub-structure distribution of Ti-Ni deposits will be systematically studied. And on that basis we further state the adding CeO2 nanopartiles on affecting the distribution of electric field around Ti cathode, and the regulating effects of textural evolution and sub-structures for Ti-Ni deposits. Experimental studies of HRTEM in-situ trace observations are innovatively applied to reveal beneficial effects of the Ce-rich dispersed phase on reinforcing grain boundary and inhibitions of other defective regions. This project is attributed to the clarifications for alloys co-deposition on the porous surface of Ti, Al and other active metals using ionic liquids-pulse electroplating technique, as well as the guidelines for Rare-Earth addition on modifications of textural regulation and performances for Ti-Ni alloy gradient composite deposits. The significance of this study is of great guiding effects and application values.

鉴于航天发动机和深海潜艇技术不断发展，对钛合金性能要求越发苛刻，然而钛金属存在耐磨性与可焊性差等表面缺陷，因此本项目基于离子液体-双脉冲技术在改性多孔钛基表面电沉积稀土复相Ti-Ni合金梯度纳米镀层。主要研究多孔钛的边缘效应对孔内-孔边缘-孔外的电场线和离子浓度分布的影响机制、多孔钛-离子液体界面的电荷转移、以及络合剂对改善Ti3+/Ni2+还原电位以促使Ti-Ni合金共沉积。耦合超声振荡和双脉冲电流特性以建立影响多孔钛表面Ti-Ni晶体生长、微结构转变的机理模型；借助HRTEM原位示踪法来阐明添加复相CeO2纳米粒子对Ti-Ni织构生长和组织演变的作用规律，以揭示Ce-rich弥散相对晶界强化及组织缺陷抑制的科学依据。本研究有助于开创离子溶液-双脉冲电沉积技术在多孔Ti、Al等活泼金属表面合金共沉积，还有利于明确稀土复相对梯度层织构生长和性能调控的作用机制，具有重要的科学意义和应用价值。

骨架多孔钛具有三维连通的开放孔结构，通过孔隙率、孔径等参数调整可对其大比表面进行活化，通过向孔道内渗透扩散合金，赋予其表面官能化，可设计出满足各种功能需求的钛基复合材料。针对钛金属表面耐磨性差、表面功能涂层与Ti界面结合差等工程难题，本项目基于H2SO4-HCl混合酸体系，在直流电压150V、冰水5℃时条件下获得孔径300-500nm多孔钛(ATO模板)，同时进行低温-碱性化学镀Ni-P来当过渡层，旨在提高Ti-Ni合金的界面结合力。研究结果表明：1) 采用超声辅助脉冲电沉积技术，通过工艺调整，在ATO模板上成功获得界面结合力良好的稀土复相Ni基合金镀层；2) 经过超声频率优化，在45+80kHz交变条件下抑制了Ni织构折优生长，由低表面能Ni(111)向Ni(222)(311)等方向转变，纳米压痕测试表明：其硬度可达15.6 GPa，弹性模量为197.2 GPa，较未加超声提高近1.5倍；3) 与纯钛比较，在多孔钛基表面电沉积镍基合金，耐磨性显著提高，摩擦系数低至0.3，在200g载荷下磨损机制由严重局部片状剥落和深“犁沟”花样转变成轻微的黏着磨损；4）对比研究添加稀土复相（CeO2）前后对Ni镀层性能影响，表明：经650℃时效处理，稀土复相Ni-CeO2纳米晶镀层显微硬度高达1000HV0.2；在850℃条件下，Ni-CeO2复合纳米晶镀层晶颗粗化被抑制，热力学稳定性增强。综上所述，在H2SO4-混合酸体系中采用直流氧化法获得异性-多孔结构表面，同时采用工艺成熟的脉冲电沉积法获得稀土复相合金镀层，操作方法简易可行，有效弥补了钛合金表面性能缺陷，有望用于航空发动机钛合金外壳等关键部位。