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1、南京航空航天大学博士学位论文 i摘摘 要要 作为钢铁材料保护镀层的纳米 CeO2/Zn-4.5%Al-RE-Mg-Ti（ZA）复合材料（ZACs） ，具有优良的耐蚀性及良好的可镀性等优点。本文首先介绍了颗粒增强金属基纳米复合材料（PRMMNCs）的研究方法及现状，并设计了一套高能超声搅拌制备装置，然后用 SEM、EDS、TEM、XRD、DSC、TG、AES、XPS 和EIS 等多种现代分析和测试手段，着重研究了纳米 CeO2的表面改性工艺、CeO2/ZA 体系的润湿特性，进而较系统地研究了纳米 CeO2p/ZA 复合材料的机械搅拌与高能超声搅拌的复合制备工艺、凝固特征、力学性能和耐蚀性能及机理
2、，最后探讨了复合材料在热镀方面的应用。 试验结果表明所设计的高能超声搅拌装置具有防氧化、控温准确、超声搅拌效果佳的特点，能够制备 MMNCs。计算结果表明 Ti 制带过渡段阶梯形超声变幅杆在熔体中的振幅为 53.41 m， 声强达到了 1.30106 W/m2， 声压幅值为 7.58 MPa。 TEM 和 AES 分析结果表明，超声表面活性剂包覆改性在纳米 CeO2表面形成了一层厚度约为 20 nm 的物理包覆层，显著提高了微粒的分散性；TG 分析结果表明 CeO2表面的包覆层在 ZACs 制备过程中能够完全炭化，热力学分析证实该炭化层能与包裹在 CeO2表面的氧化膜（主要成分为 ZnO）反应
3、，消除氧化膜对 CeO2/ZA 体系润湿的不利影响，提高体系的润湿性。 两相润湿过程力学和动力学判据的讨论结果表明，在高能超声作用下纳米CeO2粒子很难直接进入到 ZA 熔体中。因而采用卷入能力强、分散能力差的机械搅拌法制备复合材料的初步混合体，然后再用高能超声对卷入的 CeO2颗粒团进行分散，从而得到名义质量分数 16%的 ZACs。FE-SEM 和 TEM 观察的结果表明，用该法制备的 ZACs 中纳米分散较均匀。 OM 和 XRD 结果表明，ZACs 的室温金相组织主要包括呈小岛状分布的(Al)+(Zn)共析组织和呈层片状分布的 +组织。TEM 的研究结果表明，纳米 CeO2与基体界面清
4、晰、光滑，无反应产物；纳米 CeO2分布在初生和共晶相中，且与基体无明显位向关系，复合材料中的 CeO2颗粒是在初生相长大过程中被捕获的。 力学性能测试结果表明，适量纳米 CeO2的加入改善了 ZACs 的力学性能。与基体合金相比， 的抗拉强度和弹性模量明显提高， 延伸率降低。 但当纳米 CeO2质量分数大于 3%时，使 ZACs 的抗拉强度比 3%时略有下降。ZACs 的断裂机制为脆性断裂。 纳米 CeO2p/Zn-4.5%Al-RE-Mg-Ti 复合材料的高能超声制备及耐蚀性研究 ii腐蚀试验研究结果表明，ZACs 的耐蚀性能明显优于基体合金的，主要是由于加入的纳米CeO2通过提供氧空位和
5、变价作用来耗氧， 阻碍了腐蚀过程的进行，从而提高复合材料的耐蚀性。 热镀工艺的初步探讨结果表明，在本研究的热镀工艺条件下，纳米 CeO2含量为 2%的 ZACs 的热镀质量好，表面平整，没有漏镀、微裂、鼓包等表面缺陷，镀层厚度约为 30 m，而且与基体的结合力较好。 关键词：关键词：纳米氧化铈，颗粒表面改性，高能超声搅拌法，复合搅拌工艺，Zn 基复合材料，耐蚀性 南京航空航天大学博士学位论文 iiiABSTRACT The steel protective covering materials nano-CeO2p/Zn-4.5%Al-RE-Mg-Ti (ZA) nanocomposites
6、(ZACs), whose fabrication process has become one of the hot spots in metal matrix composites research, feature with good corrosion resistance, adhesion and excellent processing performance. In present study, the fabrication techniques of nano-particles reinforced metal matrix composites (PRMMNCs) we
7、re firstly introduced and compared. The high-intensity ultrasonic stirring technique, which could refine the molten alloy, disperse reinforcement particulates and enhance the wettability of the particulate/molten alloy couple, was selected to fabricate nano-CeO2 particulates reinforced Zn-based comp
8、osites. Then, a suit of high-intensity ultrasonic stirring device was assembled. Moreover, the surface modification to nano-CeO2 particulates, wetting processes between particles and molten ZA alloy, mechanical-high intensity ultrasonic combination stirring processes, solidification characteristics,
9、 mechanical properties, as well as corrosion resistance and corrosion mechanism of the ZACs were systematically investigated by the help of SEM, EDS, TEM, XRD, DSC, TG, AES, XPS and EIS. Finally, the application of the ZACs in hot dipping is discussed. The tests show that the designed ultrasonic sti
10、rring device, which has the functions of antioxidation for molten metal and accurate temperature control, as well as a good stirring effect, can be used to fabricate MMNCs. The calculation results also exhibite that the vibration amplitude, ultrasonic intensity and pressure amplitude of the titanium
11、 stepped ultrasonic transformer with a transition section in molten are 53.41 m, 1.30106 W/m2, 7.58 MPa, respectively. The TEM, FTIR and AES investigations show that nano-CeO2 particles are covered by a physical surface covering with its thickness about 20 nm by the help of ultrasonic agitation, and
12、 the distribution of the nano-particles is obviously improved. Besides, the TG result indicates that the carbonization of this covering layer can take place in the fabrication of ZACs. From classical thermodynamic point of view, reactions between the carbonization layer and zinc oxide may carry out
13、at the interface, which promotes the wetting via getting rid of the block of the zinc oxide. According to the mechanics and dynamics discussion of the systems wetting process, it is very difficult for nano-CeO2 particulates to be directly dispersed into ZA melt by high-intensity ultrasonic. Thus, na
14、no-CeO2 particulates are mechanically 纳米 CeO2p/Zn-4.5%Al-RE-Mg-Ti 复合材料的高能超声制备及耐蚀性研究 ivengulfed into ZA by machine stirring process, and subsequently dispersed by high-intensity ultrasonic stirring technique. By doing this, the ZACs with the nominal mass fractions of 1, 2, 3, 4, 5 and 6%, were obtain
15、ed. Based on the FE-SEM and TEM observations, nano-CeO2 particles could be homogeneously distributed in the ZACs. The optical microscope and SEM observations clarify that the microstructure of ZACs at room temperature consists of island-like eutectoid structure of (Al)+(Zn) and lamellar structure of
16、 +. The investigation of the solidification process of the ZACs indicates that no reaction production exists on the clear and smooth interface between CeO2 and the matrix. Furthermore, nano-CeO2 are dispered in primary and eutectic(Zn), but no ctystallographic orientation relations are found among (Zn), (Al) and CeO2. Thereby nano-CeO2 particulates in ZACs are arrested by growing grains. An optimized amount of nano-CeO2 addition could improve the mechanical properties of ZA m
