玻璃陶瓷复合材料的制备、微结构和性能

采用电子陶瓷工艺制备了一系列玻璃/锶长石陶瓷复合材料,并对复合材料进行X射线衍射分析、扫描电镜观察和性能测试。结果表明:复合材料的介电常数、热膨胀系数和显微硬度随着锶长石含量的增加而增加,而介电损耗随锶长石含量的增加而减小。锶长石含量大于50%(质量分数)的复合材料中α石英和方石英的析出增加了材料的热膨胀系数,但对材料的介电性能影响不大。所制备的复合材料具有低的介电常数(5.2~5.8)、低的介电损耗(0.10%~0.25%)、低的热膨胀系数(4.4×10-6~6.2×10-6℃-1)和低的烧结温度(≤900℃),有望用于电子封装领域。     

Direct atomic-scale imaging of ceramic interfaces

Understanding the atomic structure and chemistry of internal interfaces is often critical to developing interface structure–property relationships. Results are presented from several studies in which Z-contrast scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) have been employed to solve the atomic structures of oxide interfaces. The Z-contrast imaging technique directly reveals the projected cation sublattices constituting the interface, while EELS provides chemical and local electronic structure information. Because Z-contrast imaging and EELS can be performed simultaneously, direct correlations between structure and chemistry can be made at the atomic scale. The utility of Z-contrast imaging and EELS is demonstrated in three examples: a ZrO₂ 24° [100] symmetric tilt grain boundary, a NiO–cubic ZrO₂ eutectic interface and a Ni–cubic ZrO₂ metal–ceramic interface. The power and versatility of Z-contrast and EELS for solving interface structures in oxide systems is clearly demonstrated in these three material systems.     

Indentation method for fracture resistance determination of metal/ceramic interfaces in thick TBCs

The indentation technique has been used to measure the adhesion of plasma- sprayed ceramic coatings on metals intended for thick thermal barrier coating ( TTBC) applications. This approach provides the adhesion value as the critical strain energy release rate,Gc, of the interface, which also takes into account any residual stresses. The theoretical background of the method is outlined, and specific examples are reported with respect to the effect of substrate temperature on the metal/ceramic adhesion of thick TBCs.     

Mechanical behavior of glass and Blackglas ceramic matrix composites

Room temperature tensile tests are reported on two low-cost ceramic matrix composite materials, comprised of matrices of Blackglas^® and a proprietory glass composition each reinforced with Nicalon^® SiC-based fibers. The measured mechanical behaviors, supplemented by post-fracture analysis of fiber pullout and fiber fracture mirrors, are compared in detail to the performance predicted theoretically. This allows for an assessment of the roles of the matrix, fiber srength, residual stresses, fiber geometry, and the fiber/matrix interfacial properties in determining mechanical response. The Blackglas^® matrix cracks extensively during processing, and so the mechanical response is controlled by the deformation and fracture of the fiber bundle. The interfacial sliding resistance, τ, is determined to be ≈17 MPa and thein-situ (post-processed) fiber characteristic strength,σ_c is found to be ≈2.0 GPa, both similar to values reported in the literature for Nicalon^®/CAS-glass systems. For the glass matrix, the unidirectional and cross-ply materials show marked differences in mechanical behavior. In the cross-ply composites, τ ≈ 14 MPa andσ_c≈2.9 GPa; in the unidirectional variants, these values were 1.7 MPa and 1.6 GPa, respectively. With these data and other derived micromechanical parameters, the stress-strain and failure point of these materials was predicted using existing models, and excellent agreement with the experiments was obtained. These materials thus perform as expected given the in-situ fiber and interface properties. Notably, the cross-ply glass matrix composites exhibit high fiber strength retention and hence show tensile strengths that are better than other Nicalon^®-based materials tested to date.     

Influence of AlN addition on thermal and mechanical properties of cordierite-based glass/ceramic composites

Cordierite-based glass/ceramic composites doped with different volume fractions of AlN particles were successfully prepared by hot-pressing process. Thermal and mechanical properties of the composites were also investigated. Results show that the thermal conductivity, the flexural strength and fracture toughness of cordierite-based glass/AlN composites increase with increasing AlN content. The thermal conductivity of the composite doped with 50 vol.% AlN reaches 6.5 W/m K. By incorporation of 40 vol.% AlN, the flexural strength and fracture toughness of the composites increase 81 and 139% compared to the unreinforced cordierite-based glass matrix, respectively. XRD analysis indicated that no chemical reaction occurred between cordierite-based glass and AlN. The main strengthening and toughening mechanisms is load transfer and crack deflection.     

SiO2玻璃陶瓷与TC4钛合金的活性钎焊

分别采用活性钎料AgCuTi和TiZrNiCu对SiO2陶瓷和TC4钛合金进行了钎焊连接,使用扫描电镜和X射线衍射等手段对接头的界面组织和力学性能进行了研究.结果表明,采用两种钎料均能够实现对SiO2陶瓷和TC4钛合金的连接;SiO2/TiZrNiCu/TC4接头的典型界面为SiO2/Ti2O+Zr3Si2+Ti5Si3/(Ti,Zr)+Ti2O+TiZrNiCu/Ti基固溶体/TiZr-NiCu+Ti基固溶体+Ti2(Cu,Ni)/TC4;SiO2,AgCuTi/TC4接头的典型界面为SiO2/TiSi2+Ti4O7/TiCu+Cu2Ti4 O/Ag基固溶体+Cu基固溶体/TiCu/Ti2Cu/Ti+Ti2 Cu/TC4.当钎焊温度为880℃和保温时间为5 min时,SiO2/TiZrNiCu/TC4接头的最高抗剪强度为23 MPa;当钎焊温度为900℃和保温时间为5 min时,SiO2/AgCuTi/TC4接头的最高抗剪强度为27MPa.     

TEM investigation of interfaces during cuprous island growth

The geometry and epitaxial relationships of interfaces generated during the early-stage oxidation of Cu(1 0 0) surfaces were studied using transmission electron microscopy. The predominant orientation relationship between Cu₂O islands and the Cu substrate is cube-on-cube growth, whereby equivalent planes and directions of oxide islands and the metal substrate are matched across the interface, while other epitaxies are occasionally observed. A 6 × 7 coincidence site lattice configuration is observed at the Cu–Cu₂O interface for the cube-on-cube epitaxy. The geometry of Cu₂O–Cu interfaces is found to depend on the specific epitaxial orientations of Cu₂O islands with the Cu substrate: wedge-shaped interfaces are developed for cube-on-cube growth, and edge-on interfaces are formed for other epitaxies. These growth features are attributed to the minimization of the interface energy via the competing factors among the coincidence lattice misfit, misfit dislocations and the metal–oxide interface area.     

An experimental investigation of rotary diamond truing and dressing of vitreous bond wheels for ceramic grinding

Experiments of rotary diamond truing and dressing of vitreous bond grinding wheels were conducted to investigate the effects of feed, speed ratio, and overlap ratio on cylindrical grinding of zirconia. The applications of ceramic engine components with complex and precise form and the lack of technology for precision truing of diamond grinding wheels have driven the need to study the use of vitreous bond CBN and SiC wheels for form grinding of ceramics. Truing and grinding forces and the roundness and surface finish of ground zirconia parts were measured. By varying truing process parameters, a wide range of surface finish and roundness could be achieved. Experimental results showed that wheels trued at speed ratio below −1.0 could grind parts with fine surface finish and good roundness. The analysis of truing and grinding results showed the trend of increasing grinding force at higher specific truing energy and better surface finish at higher grinding force. The lack of speed control of the direct–drive, variable–speed truing spindle was observed and its effect on the reverse of direction of truing force at positive speed ratios was studied.     

An atomistic study of solid/liquid interfaces in binary systems

In this study, a semi-empirical Lennard-Jones/embedded atom method model is used to capture real materials behavior through the introduction of many-body forces. By means of molecular dynamics calculations, the model is used to study the dependence of the solid-liquid interface velocity on temperature for two alloy compositions. For more information contact M.I. Baskes, Los Alamos National Laboratory, PO Box 1663, MS-G755, Los Alamos, NM 87545, USA; (505) 667-1238; fax (505) 667-8021; baskes@lanl.gov.     

Spectrally-selective gold nanorod coatings for window glass

The unique optical properties of gold nanorods, which exhibit tuneable absorption as a function of their aspect ratio, suggest that they might have potential applications in coatings for solar control on windows. Here we explore the properties of coatings produced by attaching gold nanorods to the surface of glass. Such coatings can attenuate solar radiation effectively, even at very low gold contents, but the figure-of-merit,T _vis/T_sol, of our experimental coatings was close to unity, indicating that they are not spectrally selective, However, calculations are presented to show how coatings comprised of a blend of rods with aspect ratios of greater than 3 can produce coatings withT _vis/T_sol of up to at least 1.4. The maximum value possible for perfectly spectrally-selective coating in sunlight is 2.08. Unfortunately, the practical realization of such coatings requires the further development of reliable methods to scale up the production of gold nanorods of longer aspect ratios.     

The characteristics of gold films deposited on ceramic substrate

A large quantity of gold (approximately 10 tonnes yearly) is consumed, all over the world, just to decorate ceramic and glassware. Due to their advanced chemical stability gold films are used for different high technology applications. The technologies for obtaining the best “liquid bright gold” were intensively studied, but the quality of the decor coatings (films) were empirically assessed. We proposed a scientific investigation of the characteristics of gold films, deposited on ceramic substrates, from “liquid bright golds”. The composition of the film has been determined by EDS (Energy Dispersive X-ray Spectrometry). The distribution of the elements was determined at the surface of the film and in cross-section. The surface distribution of the elements was uniform. The diffusion process of the film into substrate and the migration of the substrate elements at the interface region and into the film have been highlighted.     

矿渣微晶玻璃的析晶行为与性能

以铁尾矿、硼泥和粉煤灰制备矿渣微晶玻璃,利用X射线衍射仪、扫描电镜和穆斯堡尔谱对微晶玻璃的微观结构进行研究。结果表明:矿渣微晶玻璃的主析晶相为钙铁辉石,次晶相为普通辉石和紫苏辉石;随着硼泥配入量的增加,矿渣微晶玻璃中晶体的析出量和尺寸均逐渐增加,晶体形态由枝晶向球晶及块状晶体过渡;枝晶向球晶转变可以明显改善矿渣微晶玻璃的性能,而球晶向块状晶体的转变则恶化了微晶玻璃的性能。在本实验研究的条件下,Fe2 主要分布在析晶相中,起到促进晶体析出的作用;随着硼泥配入量的增加,Fe3 含量也逐渐增加,Fe2 和Fe3 共同促进了熔体内部的晶体析出。     

高温下微晶玻璃结合剂对金刚石磨料浸润性研究

本文研究用 Li2O-ZnO-SiO2 系微晶玻璃代替普通玻璃用作金刚石砂轮结合剂以克服普通玻璃结合剂对金刚石浸润性差、热膨胀系数与金刚石相差大的缺点.研究了温度、结合剂组成及金刚石表面镀钛对Li2O-ZnO-SiO2微晶玻璃结合剂对金刚石浸润角的影响,研究发现:当温度从963 K升至993 K 时,微晶玻璃结合剂对金刚石的浸润角从129.6°降至34.5°;结合剂中的[BO3]团的存在能降低玻璃结合剂对金刚石的浸润角,Na2O对改善玻璃结合剂对金刚石浸润性无明显作用;并且金刚石表面镀钛也能明显降低微晶玻璃结合剂对金刚石的浸润角.     

二氧化铈抛光液化学机械抛光微晶玻璃的机理及优化

以纳米CeO₂为磨料自制抛光液,研究磨料质量分数、pH值、抛光液流量、抛光盘转速、表面活性剂种类和氟化铵质量分数等因素对微晶玻璃化学机械抛光的影响,分析总结CeO₂在微晶玻璃化学机械抛光中的作用机理,利用原子力显微镜（AFM）检测微晶玻璃抛光后的表面粗糙度。结果表明:当CeO₂质量分数为3%、抛光液流量为25mL/min、抛光盘转速为100r/min、pH=8.0、十二烷基硫酸钠质量分数为0.01%,氟化铵质量分数为0.7%时,抛光后微晶玻璃表面粗糙度（R_a）最低为0.72nm,材料去除速率达到180.91nm/min。      

Microindentation fracture behavior of surface modified alumina ceramic using glass infiltration

This study investigates the effect of a low expansion glass (Mg₃Al₂Si₆O₁₈) treatment on the surface fracture toughness of sintered alumina. The surface fracture toughness was determined by direct indentation method (Vickers indentations), carried out at different loads ranging from 9.8 to 196 N. The crack lengths on the surface at each load were found to be decreased (8–12%) by glass treatment and the corresponding crack resistance values increased by about 17–20%. Both sintered and glass treated specimens showed rising trend in crack resistance values as the indentation load was increased. There was also a significant increase in the Weibull modulus value of crack resistance. Improved properties of glass treated sample were attributed to the formation of a relatively larger process zone surrounding the crack, crack arrest behavior due to the compressive stresses and the crack bridging phenomena. The compressive stresses were generated from the thermo-elastic properties mismatch: (a) between the glass and the ceramic in the glass infiltrated zone, and (b) the glass–ceramic composite layer and the ceramic substrate.     

Development of electrically conductive plasma sprayed coatings on glass ceramic substrates

The production of functional coatings on glass or glass ceramic substrates is of outstanding interest in modern product development due to the specific thermophysical properties of glasses, like low or even negative CTE, low heat conductivity and high dimensional stability. Atmospheric plasma spraying (APS) is an adequate technology for the deposition of a wide variety of materials on glasses and opens new application fields for thermal spraying technology in engineering and consumer industries.Metals are the frequent solution to produce electrically conductive layers in thermal spraying operations. Concerning applications with glass ceramic as a substrate, an intermediate oxide ceramic coating is applied before depositing the metallic layer, so that the distribution of residual stresses in the composite caused during and after the deposition process due to the mismatch in the materials thermophysical properties is minimized. However, the electrical properties required for the developed coatings presented in this paper can be fulfilled using other spraying materials, like mixed phases of oxide ceramics and metal powders, or pure ceramic materials. In this way, mono-layer electrically conductive systems which ensure the required stability and adhesion of the coating can be developed, reducing as well production time and costs.In the proposed approach, the three systems, metal oxide layer-composites, ceramic-metal mixed layers and ceramic mono-layers as conductive coatings on glass ceramics were thermally sprayed with APS. The coatings were characterized in terms of residual stress distribution and electrical conductivity. The influence of the process parameters on the coating electrical and mechanical properties was analyzed using the design of experiments (DOE) methodology.     

Chemical stability of glass seal interfaces in intermediate temperature solid oxide fuel cells

In intermediate temperature planar solid oxide fuel cell (SOFC) stacks, the interconnect, which is typically made from cost-effective, oxidation-resistant, high-temperature alloys, is typically sealed to the ceramic positive electrode-electrolyte-negative electrode (PEN) by a sealing glass. To maintain the structural stability and minimize the degradation of stack performance, the sealing glass has to be chemically compatible with the PEN and alloy interconnects. In the present study, the chemical compatibility of a barium-calcium-aluminosilicate (BCAS) based glass-ceramic (specifically developed as a sealant in SOFC stacks) with a number of selected oxidation resistant high temperature alloys (and the yttria-stabilized zirconia electrolyte) was evaluated. This paper reports the results of that study, with a particular focus on Crofer22 APU, a new ferritic stainless steel that was developed specifically for SOFC interconnect applications. This paper was presented at the Fuel Cells: Materials, Processing, and Manufacturing Technologies Symposium sponsored by the Energy/Utilities Industrial Sector & Ground Transportation Industrial Sector and the Specialty Materials Critical Technologies Sector at the ASM International Materials Solutions Conference, October 13–15, 2003, in Pittsburgh, PA. The symposium was organized by P. Singh, Pacific Northwest National Laboratory, S.C. Deevi, Philip Morris USA, T. Armstrong, Oak Ridge National Laboratory, and T. Dubois, U.S. Army CECOM.     

Micro-EDM process investigation and comparison performance of Al3O2 and ZrO2 based ceramic composites

This paper investigates the micro-EDM behaviour of an Al₃O₂ and ZrO₂ based electrically conductive ceramic composites. The influence of the generator parameters on material removal rate, relative tool wear, surface quality and material removal mechanism is investigated towards the definition of suitable micro-EDM technologies. The study is based on a design of experiments, supported by a fundamental investigation of the generator parameters. Similar variations trends to the machining of steel are observed within the investigated process window, for exception of the tool wear performance. The developed EDM technologies are finally validated through the fabrication of industrial demonstrators.