【作者】 常通；

【导师】 李志友；

【作者基本信息】 中南大学 ， 材料学， 2011， 硕士

【摘要】 本论文针对铝电解惰性阳极用合金导杆目前存在的抗高温氧化性能差,在熔盐腐蚀过程中表面的氧化膜易剥落等问题,尝试在合金基体上制备一层致密的、粘附性较好的惰性涂层为研究目标。论文在国家“863”、“973”等项目的资助下,使用电沉积、电泳、氧化扩散处理法制备NiO/NiFe2O4涂层。探讨了电沉积-电泳制备Ni/Fe2O3复合涂层的工艺设计、电泳-氧化扩散处理法制备NiO/NiFe2O4复合涂层的高温下的氧化过程及形成机理,并采用研究了其抗冰晶石熔盐气氛腐蚀行为。论文主要完成了以下工作：1)利用EPD技术在稳定的水悬浮液中可以制备出较均匀、致密的Fe2O3膜。在pH值为3时,zeta电位达到最大值,高达67 mV,此时悬浮体保持较高的稳定性。电泳沉积工艺条件对沉积层的厚度与致密度有显著的影响。随沉积时间的延长,沉积速率逐渐衰减；延长电泳沉积时间有利于提高Fe2O3沉积层的厚度；通过控制沉积时间可以得到不同致密度的沉积层；通过改变阴阳两极之间的电场强度或调整两极之间的距离,电泳沉积Fe2O3的厚度会发生很大的变化。当电场强度为30V/cm,沉积时间为120s时,可以制备出均匀、无裂纹、相对密度为56%的Fe2O3膜。2)研究氧化铁粉末的形貌以及粒度对电泳沉积的影响。选用5种氧化铁粉末在同一条件下进行电泳沉积后发现,纳米粉的沉积层致密度要高于亚微米氧化铁粉的,且球形粉末的沉积层致密度高于杆状氧化铁粉的。同时研究了高温处理对杆状亚微米Fe2O3膜的致密度及膜与基体之间结合性能的影响。经1000℃与1100℃热处理4h后,Fe2O3膜的致密度有所提高,与基体之间的结合强度改善。3、)使用DSC方法确定了电泳-氧化法制备NiO/NiFe2O4复合涂层的温度范围为750-1200℃。运用Ni/Fe2O3扩散偶证明样品经1000℃氧化扩散处理后,Fe、Ni、O等元素发生了互扩散,且Fe原子的扩散速度要大于Ni原子的。4)先采用电沉积-电泳方法在Ni基体高温合金上制备电镀Ni/电泳Fe203复合涂层,再通过后续空气中进行的高温氧化处理方法来获得为NiO/NiFe2O4复合氧化物涂层。结果表明：经1000、1100和1200℃下氧化后,氧化膜中均有NiO和NiFe2O4生成。氧化温度为1000°C时涂层表面还存在没有参与反应的Fe203,但随氧化温度增加,Fe203层随之消失。温度为1100与1200℃时氧化膜中的NiO、NiFe2O4相与镀Ni基体之间形成了冶金结合,并且通过扩散形成了NiFe204析出相。Ni基体以及电镀Ni/电泳Fe2O3复合涂层在1000℃氧化时单位面积上的增重随时间增加,大体遵循抛物线规律,且电镀Ni/电泳Fe203复合涂层的单位面积上的增重大于镀Ni基体的。涂层的厚度与氧化增重随氧化温度的提高而增加。5)研究了Ni、氧化Ni基体、NiO/NiFe2O4涂层在960℃熔盐气氛中的腐蚀行为。结果表明,随着腐蚀时间的增加,Ni基体样品表面破裂、剥落,严重腐蚀；氧化Ni基体耐腐蚀性能要优于Ni基体的；NiO/NiFe2O4涂层对基体的保护性能较好,并解释了其对基体的保护机理。更多还原

【Abstract】 Inert alloy anodes is faced with a lot of problems, such as low property of high-temperature oxidation resistance and low adhesive attraction of oxide film, easy to crack in connecting interface of anode. This thesis is aimed to obtain a kind of inert coating used as connecting bar which has stable structure and better corrosion resistance. It is funded by the National High Technology Research and Development Project (863 project) and the State Key Project of Fundamental Research (973 project), using electrodeposition, electrophoresis, pre-oxidation treatment to prepare NiO/NiFe2O4 coating. And analyzing the process design of electrodeposition-electrophoresis Ni/Fe2O3 composite coating; the formation mechanism of NiO/NiFe2O4 coatings prepared by electrophoresis and pre-oxidation treatment diffusion under high temperature oxidation process and the corrosion behaviour of the oxidised composite coating was investigated at 960℃in an atmosphere consisting of a mixture of Na3AlF6-AlF3-CaF2 molten salts and air.Above all main conclusions can be drawn as followed:1) Electrophoretic deposition (EPD) technique was employed for fabricating the ferric oxide (Fe2O3) thick films on the Ni substrate. The effect of electrophoresis variables including the pH was used to investigate the influence of the stability of Fe2O3 suspension, the deposition time were used to investigate the influence of electrophoretic deposition rate, sediment thickness and density. It also studied the Fe2O3 thick film sintering performance at different temperatures. Scanning electron microscopy (SEM), zeta potential and nanoparticle size analyzer were used to characterize the deposited films. It is found that when the pH is 3, the zeta potential of suspension is up to 67mV or more, and then well dispersed suspension was obtained. The thick Fe2O3 film prepared at 30V/cm for 120s without stirring has the best properties of uniform, rack-free, and the relative density is up to 56% thick film.2) Five different morphology and particle size iron oxide powders are used on the electrophoretic deposition. The results showed that when the powders electrophored on the same conditions and it is found that the deposition of nano powder layer density is higher than the sub-micron iron oxide powder and the density of spherical powder sedimentary layer is higher than the rod-shaped iron oxide powder. The influence of high temperature on the density of micron rod Fe2O3 films and the substrate binding properties are also studied. The thick films density, intensity and bond strength with the substrate can be increased in 1000℃and 1100℃, 4h sintering.3) DSC method is used to determine the electrophoresis-oxidation diffusion treatment temperature. The results showed that the temperature is range 750-1200℃. And the Ni/Fe2O3 diffusion couple samples is also used to demonstrate the oxidized diffusion treatment at 1000℃. The results showed that Fe, Ni, O and other elements has interdiffusion, and the rate of diffusion of Fe atoms is larger than Ni atoms.4) Electrodeposition-electrophoretic deposition (EPD) technique was employed for fabricating the ferric oxide (Fe2O3) thick films on the Ni-based superalloy, and then pre-oxidation processing method was used to obtain the NiO/NiFe2O4 composite coating. Using DSC, SEM, EDS and XRD analysis method to analyze the influence of pre-oxidation temperature on the coating structure, morphology, elemental distribution and composition of the phase, and forming reaction mechanism and kinetics of the coating was also discussed. The results showed that:By high temperature diffusion processes at 1000,1100 and 1200℃for 4h respectively, the oxided film was made up of NiO and NiFe2O4.When the oxidation temperature is 1000℃, there is a not reactived Fe2O3 layer in the surface of coating, but with the oxidation temperature increasing, Fe2O3 layer is disappeared. When the the temperature is increased to 1100 and 1200℃, the NiO, NiFe2O4 phase and the Ni plating reach the metallurgical combination, but there are also mixed with some nickel-iron spinel oxides through the diffusion of transition layer. The per unit area weight of Ni substrate and electrophoretic Ni/EPD Fe2O3 coating after 1000℃pre-oxidation diffusion treatment increased with time, which generally followed the parabolic law, and the per unit area weight of Ni/ EPD Fe2O3 increased faster than electroplated Ni. The thickness and weight of oxided coating obviously increase with the pre-oxidation temperature.5) The corrosion behaviour of the Ni, pre-oxidized Ni substrate and pre-oxidized NiO/NiFe2O4 composite coating and was investigated at 960℃in an atmosphere consisting of a mixture of Na3AlF6-AlF3-CaF2 molten salts and air. The results showed that with the increasing of corrosion time, the sample of Ni surface is rupture, spalling, severe corrosion; corrosion resistance of pre-oxidized Ni substrate is better than Ni; NiO/NiFe2O4 coating has better protective performance and the protective mechanism is also explained.更多还原