Improvement in the Oxidation Resistance of Tungsten by Sol-Gel Derived Al2O3 Coating

An Al2O3 coating was prepared from aluminum isopropoxide as precursor on tungsten substrate.The dependences of crystalline and phase in Al2O3 coating on temperature were studied.The results show the coatings being compact,uniform and crack-free can be obtained by suitable experiment.The main phase of coating is α-Al2O3.Compared to the uncoated specimens,the ones with coatings synthesized by sol-gel process provide excellent oxidation resistance at high temperature.     

Al2O3/Au Composite Coating on Stainless Steel Prepared by Electro-deposition

Tritium permeation barriers on stainless steels are required in fusion technology in order to reduce the tritium permeation rate through the structural material into the cooling water system.Preparation of tritium permeation barrier Al2O3 is an important way to solve the problem of leakage of tritium permeation.It is worth to note that the noble Au is an excellent barrier of hydrogen dissolution.Al2O3/Au composite coating was designed for potential tritium permeation barrier on stainless steel.The alternation coatings have been prepared by electrochemical deposition method.The processing parameters and subsequent sinter temperature for composite coatings were optimized.The oxidation resistance of the coating has been tested.A hydrogen diffusion test simulating tritium permeation has been conducted to compare the sample with and without coating.Microstructure was examined by scanning electron microcopy(SEM).The results showed Al2O3/Au multi-alternation coatings can be prepared on the surface of stainless steel at the case of controlling processing well.The coatings have the characteristic of high temperature oxidation resistance and good hydrogen permeability barrier.The tritium permeation should be study further.     

孔道Al2O3/SiO2对NaAlH4-Tm2O3体系储氢性能的影响

以机械球磨法制备具有可逆吸放氢性能的NaAlH4-Tm2O3储氢材料体系。利用相同制备方法进一步研究两种不同孔道材料(大孔Al2O3与介孔SiO2)对NaAlH4-Tm2O3体系储氢性能的影响,测试样品的循环吸放氢性能,并对样品吸放氢前后的结构进行表征。结果表明:大孔Al2O3材料的添加并不能明显改善NaAlH4-Tm2O3体系的放氢速率和放氢量,而介孔SiO2的加入使NaAlH4-Tm2O3体系在150℃条件下5 h内的首次放氢量(质量分数)达到4.61%,高于NaAlH4-Tm2O3体系的4.27%,增加了约8.0%。此外,添加介孔SiO2的NaAlH4-Tm2O3体系放氢速率也有所提高。     

等离子弧熔覆添加Al2O3+TiO2铁基合金涂层组织和耐磨性

在Q235钢表面用等离子弧熔覆Ni-Cr-B-Si-Fe铁基合金涂层及添加不同含量Al2O3 TiO2铁基合金复合涂层,比较研究了这两种涂层的组织、显微硬度和磨损性能。结果表明,添加Al2O3 TiO2后的铁基复合涂层界面的生长形态发生变化,由初生的细长柱状树枝晶转变为小的枝晶,并且提供了形核的核心,细化了晶粒;其组织主要由晶粒细小的γ-Fe为基,以Cr23C6,Fe3C,Al2O3 TiO2为增强相的复合涂层;熔覆层的显微硬度可达600～655HV0.2。     

MoSi_2含量对MoSi_2/Al_2O_3复合涂层介电与力学性能的影响(英文)

通过喷雾干燥法制备MoSi2包覆Al2O3的壳核结构混合粉,利用该混合粉以等离子喷涂技术制备MoSi2/Al2O3复合涂层材料。研究MoSi2/Al2O3质量比涂层材料的力学和介电性能的影响。结果表明:随着MoSi2含量从0增加到45%,复合材料的抗弯强度和断裂韧性分别从198MPa和3.05MPa·m1/2增加到324MPa和4.82MPa·m1/2,随后又降到310MPa和4.67MPa·m1/2。在8.2-12.4GHz微波频率波段内,随着MoSi2含量的增加,复合材料的介电损耗增加,而介电常数的实部却呈减小趋势。这主要是由于MoSi2颗粒熔化后的凝聚及导电网络结构的形成导致电导率的增加引起的。     

等离子熔凝Al2O3/GdAlO3共晶陶瓷的制备与组织

以77mol%Al2O3和23mol%Gd2O3的共晶配比混粉,以高温等离子为热源,加热粉体使其熔融,随后以空冷和水冷的不同冷却方式实现凝固,得到不同的冷凝试样。采用X射线衍射仪和场发射扫描电镜对试样的相组成和微观形貌进行表征。结果表明,采用不同冷却工艺制备的熔凝试样均具有部分连续的Al2O3/GdAlO3共晶组织,组织致密,相界面结合良好,没有气孔和杂质;与空冷试样相比,水淬试样组织得到细化,共晶间距达到0.2μm左右。     

手工自蔓延焊接Al2O3-SiO2-CaO渣系研究

以SiO2、CaO作为造渣剂,研究其对焊渣、焊条燃烧及焊接质量的影响。结果表明,造渣剂的添加明显改善了渣液分离和焊接效果,随添加量增多,燃烧型焊条燃烧速度降低,焊渣密度发生改变但无明显变化规律,综合考虑焊接质量及操作性,SiO2和CaO的添加量分别以0.6~0.9g和0.3~0.6g为宜。手工自蔓延焊接熔渣为玻璃态和晶体共存的多元渣系,焊渣具有Al2O3、2CaO·3SiO2、CaO·Al2O3、FeO·Al2O3和金属Cu。接头断口中仍存在少量未分离的焊渣,抗拉强度达350MPa以上,满足应急抢修的力学性能需求。     

Al2O3包覆改善P2型Na2/3Fe1/2Mn1/2O2正极材料的存储性能

采用超声喷雾热解与高温固相烧结相结合的方法合成P2型Na_2/3Fe_1/2Mn_1/2O₂材料。通过X射线衍射仪、扫描电子显微镜和电化学充放电设备对材料的结构、形貌和电化学性能进行全面的表征。此外,在Na_2/3Fe_1/2Mn_1/2O₂表面包覆Al₂O₃薄层,该包覆层可以抑制Na₂CO₃·H₂O的形成,提高Na_2/3Fe_1/2Mn_1/2O₂材料的存储性能,从而改善其电化学性能。这种简单的表面改性方法为合成高性能钠离子电池正极材料提供了新思路。     

In situ formation of Zr2Al3C4/Al2O3 composites by combustion synthesis with PTFE and thermal activations

Preparation of Zr₂Al₃C₄-Al₂O₃ in situ composites was investigated by self-propagating high-temperature synthesis (SHS) involving both aluminothermic reduction of ZrO₂ and chemical activation of PTFE (Teflon). The starting materials included ZrO₂, Al, carbon black and PTFE. In addition to the conventional SHS method, the experiments were conducted by a chemical-oven SHS (COSHS) route to thermally assist the synthesis reaction. The threshold amount of 2% (mass fraction) PTFE was required to induce self-sustaining combustion. When the conventional SHS scheme was utilized, due to low combustion temperatures between 1152 and 1272 °C and insufficient reaction time, the dominant carbide forming in the composite was ZrC instead of Zr₂Al₃C₄. On the other hand, the COSHS technique increased the combustion temperature of the reactant compact to about 1576 °C, lengthened the high-temperature duration for the reaction, and prevented Al vapor from escaping away. As a consequence, Zr₂Al₃C₄-Al₂O₃ composites with a small amount of Zr₃Al₃C₅ were obtained. The microstructure of the COSHS-derived product showed that plate-like Zr₂Al₃C₄ grains were about 2 μm in thickness and 10-30 μm in length, and most of them were closely stacked into a laminated configuration.     

大气等离子喷涂Al2O3-40%TiO2涂层的组织与性能

为提高舰船关重部件的耐磨损、抗腐蚀性能,开展了大气等离子喷涂氧化铝复合涂层技术研究。在45钢表面制备Al2O3-40%TiO2陶瓷涂层,通过扫描电子显微镜、显微硬度计、电子天平、摩擦磨损试验机等仪器设备,分析该涂层的显微结构,测其显微硬度、孔隙率等性能,研究其在干摩擦条件下的摩擦磨损性能。结果表明:涂层均匀致密,孔隙率为1.86%,涂层与粘结层之间有明显的倒钩镶嵌结构;Al2O3-40%TiO2涂层的平均硬度为687.2 HV0.1,同时粘结层起到了硬度梯度作用;在干摩擦条件下,45钢主要为严重的黏着磨损,而涂层的磨损主要以层状剥离为主,伴随着少量磨粒磨损,且磨损量低于45钢。在某舰艇主机正时齿轮密封失效部位表面使用Al2O3-40%TiO2涂层,大大提高了正时齿轮的使用寿命,为舰船关重部件的维修与再制造提供了技术支持和理论参考。     

热解碳涂层对Al_2O_3纤维编织体介电及吸波性能的影响(英文)

采用化学气相沉积法在Al2O3纤维编织体上沉积热解碳涂层,利用SEM及激光拉曼光谱表征沉积与未沉积热解碳界面层的纤维编织体,并研究热解碳沉积时间对纤维电导率及编织体X波段介电吸波性能的影响。结果表明:纤维电导率及编织体复介电常数随着热解碳沉积时间的延长而增大。电子松弛极化引起复介电常数实部的增大,电导损耗引起虚部的增大。热解碳涂层可以改善Al2O3纤维编织体的吸波性能,对于沉积60min热解碳涂层的编织体,反射率在9.5GHz附近达到-40.4dB,吸波频带接近4GHz.     

烧结助剂Y2O3和Pr6O11对Al2O3陶瓷相对密度和热导率的影响

采用高分子网络法制备混合纳米粉体,研究稀土氧化物Y2O3和Pr6O11加入量对Al2O3陶瓷相对密度和热导率的影响。采用阿基米德方法测定样品的体积密度,利用激光脉冲法测量试样的热扩散率并计算得出热导率。结果表明:两种添加剂都可以降低Al2O3陶瓷的烧结温度,提高Al2O3陶瓷的热导率,其中Y2O3的促进作用较强;当保温时间相同、烧结温度为1 500~1 650℃时,Al2O3陶瓷的相对密度和热导率都随烧结温度的升高而增大;当烧结温度相同、保温时间为30~120 min时,Al2O3陶瓷的相对密度和热导率也随保温时间的延长而增大。     

等离子喷涂Al2O3-13%TiO2涂层的海水腐蚀磨损性能

基于等离子喷涂技术构筑了高耐磨、耐蚀的Al2O313%TiO2涂层（AT13涂层）,利用Rtec磨蚀试验机研究AT13涂层在干摩擦、去离子水和人工海水介质中的摩擦磨损性能,并利用电化学工作站分析了涂层在静态腐蚀和滑动磨损中的开路电位和极化曲线的变化,探讨了AT13涂层的腐蚀磨损机理。结果表明：热喷涂AT13涂层由αAl2O3、γAl2O3、金红石型TiO2和Al2TiO5相组成,其中富Ti相呈条带状分布于富Al基体中;AT13涂层在海水工况具有较好的润滑性,与干摩擦相比,其摩擦因数减小了0.15,且具有较好的稳定性;在3种工况下,AT13涂层都具有优异的耐磨损性能,海水润滑条件下,AT13涂层具有最小的磨损率,且随载荷的增加而减小;磨损过程加重了海水对涂层的腐蚀,但影响较小。     

Al2O3-TiC/Q235真空扩散钎焊界面组织及抗剪强度

为了获得Al2O3-TiC陶瓷基复合材料与Q235钢的接头,采用Ti/Cu/Ti复合中间层对Al2O3-TiC复合材料与Q235低碳钢进行了真空扩散钎焊。通过扫描电镜、能谱分析和电子探针、抗剪试验等测试方法对Al2O3-TiC/Q235扩散钎焊界面的组织、成分及结合强度进行分析。结果表明,控制加热温度为1110℃,可获得界面抗剪强度122MPa的Al2O3-TiC/Q235扩散钎焊接头,Ti/Cu/Ti复合中间层与Al2O3-TiC和Q235润湿性较好,并发生一定程度的扩散反应,在Al2O3-TiC与Q235之间形成厚度约80μm的界面过渡区,过渡区内形成的组织结构主要是Ti3AlC2,Fe2Ti,Cu和TiC。     

Development of moderate temperature CVD Al2O3 coatings

Chemically vapor deposited Al₂O₃ coatings, due to their high hardness and chemical inertness, are currently the state of art in the cutting tool industry. The conventional high deposition temperature of about 1050 °C for Al₂O₃ coatings, based on the water–gas shift process, has to a great extend restricted the development of several hybrid coatings, such as TiC/TiN/TiCN/Al₂O₃. To overcome this limitation, alternate systems to deposit Al₂O₃ at moderate temperatures have been investigated. Systems using NO–H₂, H₂O₂, NO₂–H₂ and HCOOH were identified and thermodynamic calculations were performed to evaluate them as potential sources of oxygen donors to form Al₂O₃ in the moderate temperature range of 700–950 °C. Preliminary results have clearly demonstrated that it is possible to grow moderate temperature alumina (using such alternate sources) on the TiC/TiN coated cemented carbide substrates.     

无压浸渗法制备Al2O3颗粒增强铝基复合材料

采用无压浸渗法制备了Al2O3/Al复合材料,研究了材料的微观组织与力学性能。复合材料组织致密,颗粒分布均匀,无偏聚现象。铸造态复合材料的Al2O3颗粒表面存在界面反应物,经过透射电镜观察和XRD分析确认该反应物为MgAl2O4。T6处理后界面反应程度加剧,但弯曲强度达到439.4MPa,断口中撕裂棱和韧窝的数量较少,以颗粒的脆性断裂为主。Al2O3/Al复合材料中界面反应的存在提高了润湿性,促进了无压自发浸渗。     

氧化铝掺杂对Ba0.6Sr0.4(Zr0.2Ti0.8)O3陶瓷介电性能的影响

Zr4+取代Ti4+的Ba0.6Sr0.4(Zr0.2Ti0.8)O3固溶体在降低介电常数的同时,保持了BST固溶体优异的可调性。为降低BST材料的介电损耗和介电常数,以氧化铝为改性剂对Ba0.6Sr0.4(Zr0.2Ti0.8)O3材料(BSZT材料)进行了掺杂。随着氧化铝掺杂质量分数从1%到10%增加,BSZT材料的介电常数从5000降低到了1550(100kHz),介电损耗降低到0.001(100kHz)以下,而材料的介电可调性保持在35%左右(1.5kV/mm)。X射线衍射图谱表明,烧结后得到的BSZT材料具有典型的钙钛矿结构。扫描电子显微镜观察表明,氧化铝的掺杂使得陶瓷致密度较高,晶粒均匀。     

Properties of ZrO2–Al2O3 composite as a function of isothermal holding time

Zirconia and alumina based ceramics present interesting properties for their application as implants, such as biocompatibility, good fracture resistance, as well as high fracture toughness and hardness. In this work the influence of sintering time on the properties of a ZrO₂–Al₂O₃ composite material, containing 20 wt% of Al₂O₃, has been investigated. The ceramic composites were obtained by sintering, in air, at 1600 °C for sintering times between 0 and 1440 min. Sintered samples were characterized by microstructure and crystalline phases, as well as by mechanical properties. The grain growth exponents, n, for the ZrO₂ and Al₂O₃ were 2.8 and 4.1, respectively, indicating that different mechanisms are responsible for grain growth of each phase. After sintering at 1600 °C, the material exhibited a dependency of hardness as function of sintering time, with hardness values between 1500 HV (120 min) and 1310 HV (1440 min) and a fracture toughness of 8 MPa m^1/2, which makes it suitable for bioapplications, such as dental implants.     

Study of polycrystalline Al2O3 machining cracks using discrete element method

Discrete element method (DEM) was introduced to simulate crack initiation and propagation of polycrystalline alumina during the brittle model machining process. A bonded particle model (BPM) was employed in the DEM simulations procedure to generate a particle assembly system similar to the micro-structure of the polycrystalline alumina. Particle and parallel bond properties, which were calibrated through a series of numerical tests, were subsequently used in the simulations of polycrystalline alumina cutting process and scratching tests. It is found that the cracks initiated right under or in front of the machining tool. There were many micro-cracks remained on the machined surface, some of them propagated downwards to form macro-cracks or forwards to lead material removal. Both DEM simulations and acoustic emission measure experiments have found that the fracture became acute when the normal and the tangential force changed suddenly, causing the crack number to increase. In 3D DEM scratching simulation, the surface cracks length and subsurface cracks depth linearly increased with the scratching depth, the value agreed well with the experimental results, and the surface-damage width decreased gradually with the depth to the surface, looking like half of a coin.     

Mechanochemical synthesis of Al2O3-TiB2 nanocomposite powder from Al-TiO2-H3BO3 mixture

Alumina-titanium diboride nanocomposite (Al₂O₃-TiB₂) was produced using mixtures of titanium dioxide, acid boric and pure aluminum as raw materials via mechanochemical process. The phase transformation and structural characterization during mechanochemical process were utilized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and thermogravimetric analyses (TG-DTA) techniques. A thermodynamic appraisal showed that the reaction between TiO₂, B₂O₃ and Al is highly exothermic and should be self-sustaining. XRD analyses exhibited that the Al₂O₃-TiB₂ nanocomposite was formed after 1.5 h milling time. The results indicate that increasing milling time up to 40 h had no significant effect other than refining the crystallite size.