Nb,Ce 对 Al_2O_3-中锰钢界面的影响

本文探讨了 Nb、Ce 对 Al_2O_3-中 Mn 钢界面润湿、界面反应和结构以及对界面结合强度的影响.试验表明:加入 Nb,Ce 可以使润湿角显著下降,由不润湿转化为润湿.Nb 改善润湿性的机制是界面吸附,而不产生界面反应,界面仍属于机械或润湿结合类型;Ce 改善润湿性的机制是界面反应,其反应产物主要是CeAlO_3,属反应型界面,适当的界面反应可以使界面结合强度显著提高.     

Wetting and spreading of liquid metals on ZrB2-based ceramics

The possibility to exploit commercially the peculiar characteristics of refractory metallic and ceramic materials and in particular of Zirconium diboride ceramics—a class of promising materials for high temperature applications—often depends to a great extent on the ability to join different ceramics one to the other or to special metallic alloys. As the behaviour of a metal-ceramic joint is ruled by the chemical and the physical properties of the interface, the knowledge of wettability, interfacial tensions and interfacial reactions is mandatory to understand what happens at the liquid metal-ceramic interface during joining processes. In the framework of an extensive study aimed at evaluating the wettability and the interfacial characteristics of different metal-ceramic systems, the behaviour of ZrB₂ in contact with liquid Ag and its alloys (Cu, Ti, Zr, Hf) has been studied. ZrB₂ pure, with different sintering aids or “alloyed” with other ceramic materials (SiC, Si₃N₄), have been used. The wetting and spreading experiments have been performed by the sessile drop technique under controlled atmospheres. The wetting and spreading characteristics and the interfacial reactions are discussed as a function of time, compositions of the ceramic and of the alloy involved. The interfacial morphologies, analysed by SEM and EDS, show the presence of regular interfaces and adsorption layers and of different bulk phases which are interpreted in terms of the relevant phase-diagrams.     

常规铸造工艺条件下SiCp/Al-Si复合材料中的界面反应

采用搅拌复合法制备了10%SiC／Al—5Si—Mg，10%SiC／Al—7Si—Mg(体积分数)复合材料，研究了在常规铸造工艺条件下重熔后复合材料中的界面反应。通过透射电镜和能谱分析可知，SiC界面基本上都是单一的SiC／Al及SiC／Si界面，部分界面上有MgAl2O4颗粒相形成，由于基体合金中Si的存在，生成Al2C3的有害界面化学反应得到了抑制。对不同文献中抑制Al4C3产生所需临界Si含量实验测定结果的差异进行了分析。     

Y_2O_3对铌硅化物基超高温合金硅化物渗层组织的影响

采用包埋共渗工艺在铌硅化物基超高温合金表面制备了Si-Y2O3共渗层,共渗温度为1050℃,共渗时间为10h。利用SEM,EDS和XRD等方法分析了渗剂中Y2O3添加量对渗层结构、组织形貌及其成分分布的影响,并与相同包埋渗温度和时间下单独渗Si渗层的组织进行了对比。结果表明:在渗剂中添加不同含量Y2O3后的渗层具有相似的结构,均具有明显分层的结构,由外至内依次为(Nb,X)Si2(X表示Ti,Hf和Cr)层,(Nb,X)5Si3过渡层和富Al扩散区。与单独渗Si渗层相比,渗剂中添加Y2O3没有改变渗层表层的相组成,但抑制了渗层中孔洞的产生,使相同包埋渗温度和时间处理后Si-Y2O3共渗层的组织较单独渗Si渗层的更为致密。EDS能谱分析结果表明,Y在渗层中的分布是不均匀的,在靠近过渡层与基体界面处的Y含量较高,并由内向外逐渐递减。随渗剂中Y2O3含量增加,渗层中的平均Y含量出现先增加后降低的规律。当渗剂中Y2O3的加入量为1%~2%(质量分数)时,Y2O3具有明显的催渗作用。     

C.V.D. Coating of Alumina Reinforcing Particles to Improve the Wear Resistance of H.S.S. Based Composites

C.V.D. coating of the reinforcing ceramic particles used in particulate metal matrix composites allows the control of reactivity at the particle/matrix interface. Wear resistant high speed steel-based composites containing uncoated A1₂0₃, uncoated TiC and C.V.D. coated A1₂0₃ were liquid phase sintered, then characterized using “pin-on-disc” wear testing. TiC or TiN C.V.D. coatings of A1₂0₃ were tested to determine die increase in reactivity of the particles with the liquid phases formed during sintering. This resulted in a porosity decrease at the particle/matrix interface in addition to a better ceramic/metal cohesion due to improved wettability. Reactivity and wettability were studied using differential thermal analysis, electron microprobe analysis, transmission electron microscopy, and image analysis. Results from pin-on-disc wear testing illustrated the role of the C.V.D. coating on the wear behavior of the studied materials. Lower wear rates were obtained with the composites containing TiC or TiN-coated Al₂0₃. These results showed that there is a relation between wettability of ceramic particles by the metallic phases and wear resistance of the composites.     

Superconducting properties of Ti-Nb-Hf alloys

To achieve improvements in superconducting properties of the Ti-Nb superconductor, effects of ternary additions of Hf have been extensively studied on 42 Ti-Nb-Hf alloys with compositions of 25 - 65at%Nb, 0- 15at%Hf and the balance Ti. Critical temperatures are found to depend upon Hf addition and aging temperature. In as-rolled Ti-40at%Nb-3at%Hf alloy the critical temperature is raised by about 0.3K over Ti- 40at%Nb alloy. Aging at 800°C can raise critical temperatures of high Hf alloys by 0.6 - 1.8K. The upper critical field at 4.2K of as-rolled Ti-40at%Nb-3at%Hf reaches 11.7 tesla, a value higher by 0.4 tesla than that of Ti-40at%Nb. High field critical current densities are also improved by the 3at%Hf addition. 2 step aging treatment is found effective in enhancing critical current densities of high Hf alloys. No degradation in fabricability is caused by a few at% Hf additions.     

快速凝固过程的高速摄影研究

以特制的无机盐玻璃70%Na_2SiO_3+17.7%Na_2B_4O_7+12.3%B_2O_3作为净化剂,去除液态Ni-32.5%Sn 共晶合金中的异质晶核,使过冷度达302K(0.215T_E)。采用高速摄影及快速红外测温技术研究了深过冷熔体的快速凝固行为。发现尽管过冷度超过了以往认为的均质形核临界过冷度0.2T_m,但是 Ni-32.5%Sn 共晶合金仍然优先发生界面异质形核,再辉过程中瞬时凝固速度最大可达784mm/s。     

Reactions of Hf-Ag and Zr-Ag alloys with Al2O3 at elevated temperatures

We are studying reactions of Ti, V, Zr, and Hf with ceramics as part of a program to understand fundamental reaction and bonding mechanisms in active metal brazing of ceramics. In this paper we present results of experiments with model systems comprising Ag alloys that contain different amounts of Hf or Zr that were reacted with sapphire or 99.6% alumina for different times and temperatures in a controlled atmosphere furnace. In these alloys the Ag functions as an inert solvent, which allowed us systematically to determine the effects of changes in concentration of the active element. We observed qualitative wetting and spreading tendencies of the alloys during heating and examined cross sections after cooling using electron analytical techniques. For all reaction times studied, the Hf/Ag alloys formed a discontinuous reaction layer, which was consistent with earlier high-resolution electron microscopy that showed sub-micrometer HfO₂ particles embedded in the surfaces of the Al₂O₃ grains. By contrast, initial reaction of the Zr/Ag alloys with Al₂O₃ produced a continuous interface layer. With longer reaction times, the ZrO₂ reaction product became much thicker and exhibited three distinct zones at the interface. The results suggest that the rate limiting step in the Zr/Ag reaction is the chemical reaction at the interface, whereas with Hf/Ag reaction diffusion of products away from the interface is rate limiting.     

C/C复合材料与LAS陶瓷连接的显微结构与性能

采用Y2O3-Al2O3-SiO2-TiO2(YAST)玻璃作为中间层,对SiC-MoSi2表面改性的C/C复合材料与Li2CO3-Al2O3-SiO2(LAS)陶瓷进行热压连接,所施压力为20MPa,保温时间为30min,连接温度分别为1150℃,1200℃,1250℃,1300℃。利用SEM,EDS和BEI(背散射电子像)对SiC-MoSi2涂层,连接界面的形貌和断口进行了分析,研究结果表明,SiC-MoSi2涂层与基体结合紧密,Si、C元素在界面处呈梯度状分布,形成厚度约为15μm的过渡层。YAST玻璃与基体润湿良好,接头的剪切强度可达26.21MPa。     

掺杂 Al_2O_3对 Ba_2Ti_9O_(20)相形成的影响

本文研究了在BaO-TiO_2-SnO_2固相反应系统中掺杂 Al_2O_3对 Ba_2Ti_9O_(20)相形成的影响。实验结果表明,即使掺杂少量的 Al_2O_3,在反应过程中 Ba_2Ti_9O_(20)相也变得更容易形成。微观结构分析结果表明,Ba_2Ti_9O_(20)晶体结晶时,由于具有层状结构特征,往往会出现结构层间应力;这种应力会严重制约Ba_2Ti_9O_(20)晶体的形核和长大。掺杂少量 Al_2O_3后,能形成与 Ba_2Ti_9O_(20)晶体共生的 BaAl_2Ti_6O_(16)晶体;这种共生机制抑制了应力的发展。Al_2O_3改善了 Ba_2Ti_9O_(20)结晶的动力学条件,促进了 Ba_2Ti_9O_(20)相的形成。     

Interaction of TEMAHf precursor with OH-terminated Si (001) surface: a first principles study

We performed a first principles study to investigate the interaction of tetrakis-ethylmethylaminohafnium (4[(C2H5)(CH3)N]Hf, TEMAHf) precursors with an OH-terminated Si (001) surface that is the initial stage of atomic layer deposition (ALD). When TEMAHf reacted on the OH-terminated Si surface, there were two reaction mechanisms. One was the reaction with one -OH, and the other was the reaction with two -OH's. When TEMAHf reacted with an -OH on the Si (001) surface, an ethylmethylamine ((C2H5)(CH3)NH, EMA) was produced as a by-product and the trikis-ethylmethylaminohafnium group (3[(C2H5)(CH3)N]Hf) was attached to the O atom of the -OH. There were five reaction sites for TEMAHf to react with two -OH's to form the dikis-ethylmethylaminohafnium group (2[(C2H5)(CH3)N]Hf): Inter-dimer, intra-dimer, inter-row, cross-dimer, and cross-row. The reaction with two -OH's on the inter-dimer, intra-dimer, and inter-row sites were more favorable than the reaction with one -OH. Since the inter-dimer reaction was the most favorable, the energy barrier on the inter-dimer site for the reaction of the trikis-ethylmethylaminohafnium group with -OH to form the dikis-ethylmethylaminohafnium group was calculated, and the result was 0.19 eV. An extra energy of 0.25 eV was needed to remove EMA from the surface. Four TEMAHf's reacted with the surface and these reactions were exothermic by -7.77 eV, and the calculated Hf coverage of the first-half ALD cycle was 1.67 x 10(14)/cm2.     

用溶胶－凝胶法在碳纤维表面涂覆Al_2O_3

本文研究用溶胶－凝胶方法在碳纤维表面涂覆Ａｌ＿２Ｏ＿３，的工艺对涂层性能、结构及对纤维强度、抗氧化性能等的影响。结果表明：所配溶胶质量好，涂覆工艺合适，可在纤维表面得到均匀、连续的Ａｌ＿２Ｏ＿３，涂层；该涂层不仅改善了纤维的抗氧化性能，而且还能保持纤维原有的强度；改善与熔铝的润湿性，为复合材料的制备提供方便。     

Defects and interface states related photocatalytic properties in reduced and subsequently nitridized Fe3O4/TiO2

The Fe_3O_4@TiO_2 catalyst was reduced in a mixed H_2/N_2 atmosphere at temperatures of 400, 600, 800 and 1000?C in order to produce the oxygen vacancies(O_v) and Ti~(3+); Simultaneously, Fe_3O_4 was reduced to Fe, a strongly magnetic material, beneficial for the magnetic separation after the photo-degradation.The optimal catalyst was obtained at the reducing temperature of 800?C, which possesses the good photocatalytic performance and recycled activities; Moreover, its saturation magnetization Msis highest,reaching 23.8 emu g~(-1) which improves the magnetic separability. This optimal catalyst was subsequently treated in the NH_3 atmosphere at temperatures of 500, 600 and 700?C, aiming to investigate the effects of N-doping in TiO_2. The 600?C treated catalyst exhibited the optimal photocatalytic performance. The factors that affect the photocatalytic performance are revealed and discussed in detail, including the ratio of Ovand N dopant in TiO_2 as well as the interface states between TiO_2 and the magnetic particles.     

Wetting in the ThO2/Me (Me?=?Ce, Al, U) systems: an example of the liquid phase properties role in reactive wetting

In this study, the wettability properties and chemical reactions in ThO₂ (~90?% dense)/Me (Me?=?Ce, Al, U) were measured. Sessile drop experiments were carried out at 1000, 1150, and 1250?°C for 60?min and the final apparent contact angles measured were 22°?±?2°, 45°?±?2°, and 135°?±?3°, respectively. Chemical reaction at the interface was detected only in the case of ThO₂/Al, where a thick (100–200?μm) C⁴ structure layer containing α-Al₂O₃ and Th-rich Al metallic phases were found. In this study, correlation between the thermodynamic properties of the binary Me–Th melts, chemical reaction at the interfaces, and spreading behavior was demonstrated. The Th–Al liquid solution has a negative departure from ideality and the chemical reaction at the ThO₂/Al interface was massive. The Th–U liquid solution displays a positive departure from ideality and the chemical reaction at the ThO₂/U interface was negligible. Th–Ce liquid solution displays a close to ideal behavior with a small positive departure from ideality, which promoted spreading without significant Th dissolution in the Ce melt and no detectable formation of new oxides at the interface. It is proposed that the mild chemical reaction in the ThO₂/Ce system is ideal for pressure-free infiltration processes. The dominance of the liquid solution properties concerning wettability behavior and chemical reaction at the interface was demonstrated using thermodynamic evaluation.     

铌硅化物基超高温合金Si-Y2O3共渗涂层的组织及其高温抗氧化性能

采用Si-Y₂O₃包埋共渗工艺在铌硅化物基超高温合金表面制备Y改性的硅化物涂层, 研究其在1250℃的恒温氧化性能. 采用扫描电镜(SEM)、能谱(EDS)与X射线衍射(XRD)分析Si-Y₂O₃共渗涂层氧化前后的物相组成和组织变化. 结果表明：涂层具有明显分层的结构, 由外至内依次为(Nb,X)Si₂(X表示Ti, Hf和Cr)外层和(Nb,X)₅Si₃过渡层, 在过渡层与基体之间有不连续分布的细小(Cr,Al)₂(Nb,Ti)块状沉淀. EDS分析表明, 涂层中的Y分布是不均匀的, (Cr,Al)₂(Nb,Ti)相的Y含量为0.94at%左右, 而(Nb,X)Si₂和(Nb,X)₅Si₃相的Y含量为0.46at%～0.57at%. 经1250℃分别氧化5, 10, 20, 50和100h后, Si-Y₂O₃共渗涂层保持其原始的相组成, 并在其表面形成以TiO₂、 SiO₂和Cr₂O₃组成的致密混合氧化膜, 且与基体结合良好.     

Migration of Oxides in a Composite Coating and Its Effect on Inhibiting Coating Degradation

Based on the fact that the dispersed rare earth oxide particles in an electrolytic co-depositedNi-R_2O_3 layer migrated and accumulated at the substrate/coating interface immediately afteraluminizing,the mechanism of migration of the oxides and its effect on the behaviour of degradationof the coatings oxidized at 1100℃ were studied in this paper.The Ni-R_2O_3 layers were treated invacuum at 900℃ and aluminized at 1100℃ separately.The results indicated that the migration andaccumulation of R_2O_3 particles were favorable to the gathering of R_2O_3 at higher temperatures,andthe small size oxides were easier to migrate and gather.The drawing effect of grain boundary wasused to explain this behaviour.The microstructures of the coatings oxidized at 1100℃ were ob-served.It was found that the coating degradations were related to the amount and distribution of theaccumulated R_2O_3 at the alloy/coating interface.Three typical kinds of the accumulated layerswere identified.The continuous oxide layers acted as diffusion barrier which could inhibit the coat-ing degradation effectively.     

包覆型α-Al_2O_3粉体的制备及表征

以平均粒径为22μm和0.5μm的α-Al2O3粉体为起始原料(以下分别简称Al2O3(C)和Al2O3(F)),分别以聚乙烯亚胺(PEI)和聚甲基丙烯酸铵(APMA)为聚合物电解质,采用非均相凝固法将Al2O3(F)颗粒均匀地包覆在Al2O3(C)粉体表面.重点考察了聚合物电解质的吸附时间、Al2O3(C)/Al2O3(F)的质量比、两种分子量的PEI对包覆型氧化铝粉体制备的影响.当Al2O3(C)/Al2O3(F)的质量比为1∶3,经过分子量约为60 000的PEI处理2 h的Al2O3(C)粉体表面均匀地包覆了Al2O3(F)颗粒(经APMA处理2 h).采用该包覆型粉体制备出片状多孔支撑体,其孔隙率为35.8%,平均孔径为2.9μm,纯水通量为205 m3/(m2.h.MPa).     

铝合金熔体氧化制备Al2O3 / SiC/ Ni/ Al-Si多相模糊界面陶瓷基复合材料

针对Al₂O₃ / Al 复合材料中金属相Al 对其高温性能的不利影响, 本试验在高温下将铝合金熔体氧化渗透到注浆成型的SiC/ Ni 多孔预制体中, 制备了Al₂O₃ / SiC/ Ni/ Al-Si 多相陶瓷基复合材料。借助光学显微镜、电子显微镜(SEM) 、X 射线衍射仪(XRD) 、波谱仪( EDS) 等手段分析了预制体和复合材料的相组成、微观结构及界面特征。结果表明, 复合材料的主晶相为Al₂O₃ 与SiC , 相间存在Al (Si) 复合氧化物、NiAl₂O₄ 及Ni 与Al-Si 合金相, 各相界面处成分呈连续过渡变化趋势, 构筑了具有模糊界面特征的多相复合材料。      

Direct liquid injection metal-organic chemical vapor deposition of HfO2 thin films using Hf(dimethylaminoethoxide)4

Hf(OCH₂CH₂NMe₂)₄, [Hf(dmae)₄] (dmae=dimethylaminoethoxide) was synthesized and used as a chemical vapor deposition precursor for depositing Hf oxide (HfO₂). Hf(dmae)₄ is a liquid at room temperature and has a moderate vapor pressure (4.5 Torr at 80 °C). It was found that HfO₂ film could be deposited as low as 150 °C with carbon level not detected by X-ray photoelectron spectroscopy. As deposited film was amorphous but when the deposition temperature was raised to 400 °C, X-ray diffraction pattern showed that the film was polycrystalline with weak peak of monoclinic (020). Scanning electron microscope analysis indicated that the grain size was not significantly changed with the increase of the annealing temperature. Capacitance–voltage measurement showed that with the increase of annealing temperature, the effective dielectric constant was increased, but above 900 °C, the effective dielectric constant was decreased due to the formation of interface oxide. For 500 Å thin film, the dielectric constant of HfO₂ film annealed at 800 °C was 20.1 and the current–voltage measurements showed that the leakage current density of the HfO₂ thin film annealed at 800 °C was 2.2×10⁻⁶ A/cm² at 5 V.     

Influence of particulate morphology on microstructure and tribological properties of cold sprayed A380/Al_2O_3 composite coatings

In this study, three kinds of A380/Al_2O_3 composite coatings were prepared by cold spray(CS) using spherical, irregular and spherical + irregular shaped Al_2O_3 particulates separately mixed in the original A380 alloy powders. The influence of Al_2O_3 particulates' morphology on the microstructural characteristics(i.e.retention of Al_2O_3 content in coatings, coating/matrix interfacial bonding, pore size distribution and morphology etc.) and wear performance of the coatings was investigated by scanning electron microscopy(SEM), X-ray computed tomography(XCT) and 3-D optical profilometry. Results indicated that the spherical Al_2O_3 shows obvious tamping effect during deposition process. As a result, the interface showed a wavy shape while the matrix and particulates were mechanical interlocked with much improved adhesion. In addition, the porosity of the coating was minimized and the pores exhibited curved spherical structure with reduced dimensions. The irregular Al_2O_3 particles predominantly displayed the embedding effect together with fragmentation of Al_2O_3 particulates. Consequently, poor coating/matrix interfacial bonding, high porosity and the formation of angular-shaped pores were resulted in the coating. Dry sliding wear tests results revealed that the wear resistance of the coating is directly related with the retained content of Al_2O_3 in the coating. The coating containing irregular Al_2O_3 particulates displayed superior wear performance with its wear rate one seventh of that of the pure A380 alloy coating. The coating containing both kinds of Al_2O_3 particulates showed mixed characteristics of above two kinds of Al_2O_3 composite coatings.