【作者】 李岩；

【导师】 凌国平；

【作者基本信息】 浙江大学 ， 材料科学与工程， 2011， 博士

【摘要】 国际热核聚变实验堆(ITER)计划中,包层模块等关键部件表面需要制备阻氚涂层,以防止氚渗透。目前公认最被认可的阻氚涂层是具自修复性能的Al2O3/Fe-Al涂层,但如何在保持零部件力学性能的同时,适合异形件表面无缺陷阻氚涂层的制备,仍然是ITER计划中的技术难题之一。本论文提出了一种阻氚涂层制备的新技术路线：首先通过室温熔盐电沉积技术在金属表面镀铝；之后通过低温热处理在表面制备Fe-Al合金层；并进一步通过低温氧化,在Fe-Al涂层表面制备A1203膜。本文紧扣该技术路线,采用室温熔盐电沉积表面工程新技术和热处理、氧化等技术,以及CV曲线、XRD、SEM、EDS、XPS等手段,深入研究了不同金属基体上前处理工艺及电沉积参数等对室温熔盐电沉积铝镀层结合力及形貌的影响,探讨了热处理温度、时间,以及基体成分、结构、表面粗糙度等因素对Fe-Al涂层组成及相转变的影响规律,详细考察了基体与涂层之间空洞的形成机理及影响因素,并对不同金属基体上Fe-Al涂层的氧化进行了研究,对所得涂层进行了阻氚性能测试。得到了以下结果：利用酸性AICl3-EMIC室温熔盐对201、HR-2奥氏体和1Cr17铁素体不锈钢基体进行1 A/dm2、30 min阳极活化处理,可去除表面氧化膜；活化电流密度过低,基体产生局部腐蚀；更高的电流密度会导致镀液分解。室温下、0.5-3 A/dm2电流密度电沉积,可得到致密铝镀层,电流密度增加,晶粒细小,过高产生树枝状析出。电流密度2A/dm2时,5-40 min内,电流效率接近100%,铝镀层厚度与时间成线性上升关系；可通过控制电沉积时间制备不同厚度的铝镀层。201奥氏体不锈钢上17μm的铝镀层,经620℃-680℃低温热处理,可获得含铬、镍、锰合金元素的Fe-Al涂层。高于铝熔点时,在2～240 min范围内,随热处理时间增加,铝层逐渐消失,FeAl3和Fe2A15相继形成；铝层完全消失后,扩散以FeAl3为铝源继续进行,Fe2Al5相厚度继续增加,同时在基体和镀层之间形成FeAl相。低于铝熔点时,涂层组织转变有同样的规律,只是所需时间更长。当基体为1Crl7铁素体及HR-2奥氏体不锈钢时,热处理温度及时间对铝镀层组织转变的影响规律相似。依扩散理论计算可知,铝镀层较薄时,可通过低温短时间热处理制备韧性的FeAl涂层。HR-2上4μm的薄铝镀层经670℃、4h热处理后,可得到厚度均匀的韧性FeAl层,FeAl层及界面中无裂纹、空洞等缺陷。不同基体对低温热处理制备的Fe-Al涂层形貌有较大影响,各Fe-Al合金相中都固溶基体中的铬、锰、镍合金元素。基体中合金元素铬、镍、锰等的存在抑制了Fe2A15相的舌状生长,使201、HR-2奥氏体和1Crl 7铁素体不锈钢上Fe-Al涂层与基体的界面平坦。FeAl层厚度与热处理时间关系曲线遵循抛物线关系,基体的不同影响FeAl相的生成速度：1Cr17铁素体基体上FeAl相的生成速度最慢,而Q235基体上FeAl相的生成速度最快。镀铝基体在热处理时,会在FeAl相/基体界面上形成空洞。空洞的形成与热处理的温度、时间、基体粗糙度、晶体结构和合金元素等因素有关。镀铝的1Cr17基体在低于铝熔点的640℃下热处理100 h而无空洞,而在高于铝熔点的670℃热处理时,20 h便可观察到空洞,50h出现明显的圆形空洞；粗糙基体表面增加了铝的扩散通量,更易产生空洞,1Cr47喷砂粗化镀铝后,670℃热处理20 h的空洞形貌与抛光态镀铝热处理50h相似；面心立方结构的HR-2和201奥氏体不锈钢较体心立方结构的1Cr17不易形成空洞；HR-2即使喷砂处理,740℃、24 h热处理也观察不到空洞。采用室温熔盐镀铝制备铝化物涂层时,铝镀层越薄,铝的浓度梯度下降快,同时铝镀层薄,可采用低的热处理温度,这些因素都有利于抑制空洞的形成。1Cr17不锈钢上镀铝+热处理制备的Fe-Al涂层,可以在740℃大气气氛氧化获得A12O3,但氧化膜中含有Fe2O3,且涂层与基体之间存在明显的空洞缺陷。HR-2不锈钢上镀铝+热处理制备的Fe-Al涂层,在690℃-740℃大气气氛氧化,涂层与基体之间没有空洞等缺陷,得到的氧化膜中含Fe203和A12O3；在10-2Pa低氧势环境下,经700℃、80 h氧化,可在表面得到完整的A12O3膜,低氧势环境氧化可抑制铁氧化物的形成；Fe-Al涂层中铬的存在促进完整A12O3膜的形成。740℃对涂层阻氚性能进行测试,所得涂层渗透率降低因子PRF可达431。因而室温熔盐镀铝可以在不锈钢表面制备性能优异的阻氚涂层,是一条适合异型件表面阻氚镀层制备的新技术路线。本文还在室温熔盐镀铝成功应用于ITER计划中阻氚涂层制备的基础上,利用AlCl3-EMIC室温熔盐无水、无氧的特点,以易氧化的核材料耐蚀保护为目标,以化学性质活泼的La-Ce稀土与AZ91D镁合金为对象,进行了室温熔盐镀铝的研究,重点考察镀层与基体的结合,得到以下重要的结论：La-Ce稀土在煤油中进行打磨,并在氩气保护气氛中烘干,可有效去除表面氧化膜,并防止氧化膜的再产生；而AZ91D镁合金通过浓度为10wt.%的稀磷酸浸蚀20s,可在表面形成磷酸盐膜,抑制基体的再氧化。经上述前处理,在两种活泼金属表面得到了镀层致密、结合良好的纯铝镀层。更多还原

【Abstract】 In the International Thermonuclear Experimental Reactor (ITER) project, tritium permeation barrier is necessary on the surface of TBM (Test Blanket Module). Al2O3 /Fe-Al layer with self-repairing performance is recognized as the best tritium permeation barrier. But how to prepare tritium permeation barrier on special-shaped surface and maintain mechanical performance of the matrix at the same time is still one of the technical problems. In this paper a new preparation technology of tritium permeation barrier is presented:at first, aluminum is electrodeposited on metal surface at room temperature molten salt; then Fe-Al alloy coating is prepared on the surface through low temperature heat treatment, and further Al2O3 film is prepared on the surface of the Fe-Al coating through low temperature oxidation.By means of the technology of electrodeposition at room temperature molten salt, heat treatment and thermal oxidation and the methods such as CV, XRD, SEM, EDS and XPS, the effects of pretreatment on different metal matrix and electrodeposition parameters at room temperature molten salt on adhesion and morphology are studied, and further the effects of heat treatment temperature, time, matrix composition, matrix structure and surface roughness on phase structure and phase transformation of Fe-Al coating are studied. At the same time the formation mechanism and influence factors of the voids between the coating and matrix are studied. At last the oxidation of Fe-Al coating on different metal matrix is studied and tritium resistivity test is carried out. Through the research, the following conclusion can be concluded:Through anode activation treatment of 1 A/dm2,30 min at AlCl3-EMIC room temperature molten salt on 201, HR-2 austenitic and 1Cr17 ferritic stainless steel matrix, oxide film on the surface is removed; if the activation current density is too low, localized corrosion will be produced on the matrix and higher current density would lead to the plating liquid decomposition. Compact aluminum coating will be electrodeposited with the current density of 0.5-3 A/dm2, and with the increase of current density, grain size become smaller. Dendritic crystal will appear if current density is too high. Current efficiency is close to 100% with the current density of 2 A/dm2, during 5-40 min. Aluminum coating thickness linear increase with the time increase. Through controlling the electrodeposition time, different thickness of aluminum coating can be obtained. After the aluminum coating of 17μm on 201 austenitic stainless steel is heat treated at low temperature of 620℃～680℃, Fe-Al coating with the alloy element of chrome, nickel will form. The aluminum layer gradually disappeared with the heat treatment time increases at the temperature higher than aluminum melting point in 2～240 min range. FeAl3 and Fe2Al5 form in succession; after the aluminum layer disappear completely, diffusion continue with FeAl3 as aluminum source and the thickness of Fe2Al5 phase continues to increase, at the same time FeAl phase forms between the coating and the matrix. Below the melting point of aluminum, the rule of the phase transformation is similar, just the transformation time is longer. When the matrix is 1Cr17 ferrite and HR-2 austenitic stainless steel, the rule is similar. According to the diffusion theory, FeAl layer can be prepared through short time heat treatment at low temperature. After aluminum coating of 4μm on HR-2 is heat treated at 670℃/4h, FeAl layer with uniform thickness can form and there is no defects such as cracks and voids at the interface and FeAl layer.The morphology of Fe-Al layer prepared by low temperature heat treatment is different on different matrix. Alloy elements of chromium, manganese, nickel appears in Fe-Al alloy phase as the solid solution. The exist of chromium, nickel, manganese inhibit the growth of Fe2Al5 phase like tongue, so that the interface between Fe-Al layer and 201, HR-2 austenitic and 1Cr17 ferritic stainless steel is flat. The curve of FeAl layer thickness with heat treatment time is a parabola. The generating speed of FeAl phase is different:FeAl generation rate on 1Cr17 ferrite matrix is the slowest, and the rate on Q235 matrix is the quickest.Voids appears at the interface of FeAl and matrix during the heat treatment. Void formation is related with heat treatment temperature, time, roughness of matrix, crystal structure and alloy elements. At the heat treatment temperature of 640℃below the melting point of aluminum, there is no void on the interface between the FeAl layer and 1Cr17 matrix even the heat treatment time is 100 h, but at 670℃above the melting point of aluminum, voids are observed after 20 h heat treatment. Circular voids are observed after 50 h heat treatment. Rough surface of the matrix increases the aluminum diffusion flux, so voids forms easier. The void morphology of sandblasted 1Cr17 heat treated with 670℃/20 h is similar with polishing 1Cr17 heat treated with 670℃/50. Voids form easier on the interface of HR-2 and 201 austenitic stainless steel with face-centered cubic structure than 1Cr17 with body-centered cubic structure. There is no void even after 740℃/24 h heat treatment on sandblasted HR-2 matrix.In the atmosphere, Al2O3 can be observed after the Fe-Al layer on 1Cr17 thermal oxidized at 740℃, but Fe2O3 is observed too, and there exist voids between Fe-Al and the matrix. The oxide film containing Fe2O3 and Al2O3 after the Fe-Al layer on HR-2 thermal oxidized at 690℃-740℃in the atmosphere and there is no void at the interface. But in 10-2 Pa hypoxia potential environment, intact Al2O3 film can be obtained after thermal oxidation at 700℃/80 h. Hypoxia potential can inhibit iron oxide formation. Chromium in Fe-Al layer promotes the formation of intact Al2O3 film. Tritium resistivity test is carried out at 740℃, the permeability reduction factor PRF is 431.In the base of the successful application of electrodeposition aluminum on prepare tritium permeation barrier at room temperature molten salts in the ITER project, the studied of electrodeposition aluminum on active La-Ce rare earth and AZ91D magnesium alloy in AlCl3-EMIC at room temperature molten salt is carried out which focuses on the adhesion between coating and matrix. The following important conclusions can be drawed:oxide film can be effectively removed after the La-Ce rare earth polished in kerosene and dried in argon atmosphere and this pretreatment can prevent the oxide film to produce. After the AZ91D magnesium alloy etched for 20 seconds in dilute phosphoric acid with concentration of 10 wt.%, phosphate film can be obtained on the surface which can inhibit the formation of oxide film. After the pretreatment, dense and pure aluminum coating with good adhesion can be obtained on the surface of the two kind of active metal.更多还原