复合陶瓷的应用发展是未来新材料市场的主题

陶瓷基复合材料不是传统意义上的陶瓷,它是以陶瓷为基体与各种纤维复合的一类复合材料。其主要基体有玻璃陶瓷、氧化铝、氮化硅等,具有高温强度好、高耐磨性、高耐腐蚀性、低膨胀系数、隔热性好及低密度等特性,而且资源也比较丰富,有广泛的应用前景。针对陶瓷基复合材料成为争夺国际市场的制高点,分析了陶瓷基复合材料的研发受到重视,阐述了复合陶瓷材料的特点,介绍了陶瓷基复合材料的应用领域,同时指出了节能环保的车用陶瓷基结构复合材料大有作为。     

复合陶瓷的应用发展是未来新材料市场的主题

陶瓷基复合材料不是传统意义上的陶瓷,它是以陶瓷为基体与各种纤维复合的一类复合材料。其主要基体有玻璃陶瓷、氧化铝、氮化硅等,具有高温强度好、高耐磨性、高耐腐蚀性、低膨胀系数、隔热性好及低密度等特性,而且资源也比较丰富,有广泛的应用前景。针对陶瓷基复合材料成为争夺国际市场的制高点,分析了陶瓷基复合材料的研发受到重视,阐述了复合陶瓷材料的特点,介绍了陶瓷基复合材料的应用领域,同时指出了节能环保的车用陶瓷基结构复合材料大有作为。     

氧化铝-莫来石高温复合陶瓷改性研究

以氧化铝、莫来石、氧化锆粉体为原料制备了氧化铝-莫来石-氧化锆复合陶瓷.使用密度测试仪、抗折强度测试仪、XRD和SEM等手段对材料的密度、力学性能进行了综合分析,尝试对影响复合陶瓷热震性能的因素及作用机理进行了讨论.研究结果表明:氧化锆弥散分布于基体晶界处,填充了基体颗粒间隙,抑制了基体晶粒长大,阻碍了裂纹扩展,提高了复合陶瓷的致密性和力学性能;ZrO2的t-m转变使基体内部产生一定的压应力区域,诱发显微裂纹的产生,分散主裂纹尖端应力,增强复合陶瓷的强度.     

对几种陶瓷材料抗磨性的浅探

初步探讨了在摩擦磨损系统中３种陶瓷材料──氧化锆增韧氧化铝（ＺＴＡ）、部分稳定氧化锆（ＰＳＺ）、氧化锆增韧莫来石（ＺＴＭ）和高铬铸铁材料的耐磨性。通过比较，陶瓷材料比金属材料具有更强的抗摩擦磨损能力，而且在这３种陶瓷材料中，ＺＴＡ的耐磨性最好，其磨损机理为塑性切削机制和脆性剥离机制。     

多晶氧化铝纤维对莫来石—氧化锆陶瓷材料的增强研究

以电熔莫来石、半稳定氧化锆和α-氧化铝微粉为主要原料,制备莫来石—氧化锆陶瓷材料。在材料中分别外加了（V%）0、5%、10%、15%和20%的多晶氧化铝纤维,并将试样在1500℃保温3h烧成,制备出氧化铝纤维增韧的莫来石—氧化锆复相陶瓷。研究了氧化铝纤维对试样的加热线收缩率、常温耐压强度、常温抗折强度和热震稳定性的影响。结果表明：加入适量的多晶氧化铝纤维能够显著降低莫来石—氧化锆复相陶瓷的加热线收缩率,大幅度提高其常温抗折强度和热震稳定性,而常温耐压强度只有轻微下降。     

对称型梯度功能陶瓷材料的抗热震参数

采用摄动法推导出第三类边界条件下无限大对称型梯度功能材料(functionally gradient materials，FGM)平板的瞬态温度场及瞬态热应力场表达式。基于陶瓷材料的临界应力断裂判据，通过求解无限大对称型梯度功能陶瓷平板表面达到其局部断裂强度的时间，建立了引起其表面临界热应力的临界温差△Tc的表达式，并以此作为对称型梯度功能陶瓷的抗热震参数。通过计算实例并与均质陶瓷材料对比，分析了材料的热—物理性能分布规律对其抗热震性的影响。对高抗热震性复合陶瓷材料的研究开发具有实际意义。     

纤维增强陶瓷的研究

本文研究了制备增强复合材料(纤维增强陶瓷)的可行性,采用聚苯酚——甲醛或聚乙烯醇作为增塑剂,以碳纤维和莫来石纤维为增强材料,利用不同种类的氧化铝陶瓷作为基体材料。检测数据表明,增强复合材料能获得许多优良的性能,如:热震性能好、耐化学腐蚀性能好和机械强度大等。同时,以工业氧化铝粉末作为基体材料的增强复合材料(纤维增强陶瓷)的密度比以纯氧化铝粉末作为基体材料的增强复合材料(纤维增强陶瓷)的密度略低一些。事实上,增强复合材料(纤维增强陶瓷)的密度主要是由所采用的增塑剂的数量和种类决定的,增加纤维材料的添加量,反而会减小增强复合材料(纤维增强陶瓷)的密度,同时纤维的种类及其添加量又严重地影响增强复合材料(纤维增强陶瓷)的收缩率。     

添加聚醚醚酮对Al_2O_3陶瓷组织及性能的影响（英文）EI北大核心CSCD

为改善氧化铝陶瓷的耐磨性和耐蚀性,用喷雾造粒的方法将PEEK(聚醚醚酮)加入到由亚微米氧化铝粉末制备的团聚粉中,制备了Al_2O_3陶瓷基复合涂层材料。用扫描电子显微镜分析了复合材料的组织结构,测试了复合陶瓷涂层的耐磨性和耐腐蚀性,并与纯氧化铝的性能进行对比。结果表明:添加PEEK的Al_2O_3复合陶瓷涂层在磨损试验中的摩擦系数低于Al_2O_3陶瓷,摩擦磨损更稳定,耐磨性更高,在20和30 N载荷下,复合涂层的平均摩擦因数分别为0.593 0和0.589 6,降低了15.8%和15.6%,平均磨损量分别降低了15.7%和17.6%;相对于Al_2O_3陶瓷涂层,复合陶瓷涂层的自腐蚀电位提高15.3%,电流密度降低47.5%,耐腐蚀性提高。     

莫来石涂层对氧化铝基体力学性能的影响

陶瓷材料的预应力增强已经被证明有效，但是这种表面预应力对其他力学性能的影响如何仍不明晰，本工作将探讨表面残余压应力对复合构件的综合力学性能的影响，包括弯曲强度、弹性模量、断裂韧性、硬度以及损伤容限。为了实现表层压应力以及相适配的界面剪切应力，按质量分数比1∶1将莫来石和氧化铝混合磨成浆料涂覆在预烧后的氧化铝基体上，经无压烧结后，涂层与基体紧密结合，随着温度下降，2种材料不同的收缩率和界面约束形成表层残余压应力，从而实现氧化铝复合陶瓷的预应力强化，进而测试了该材料的各项力学性能。结果表明：预应力涂层有效提高了基体材料的弯曲强度，提高了38.9%；断裂韧性提高了36.5%，弹性模量稍降、硬度下降代表了涂层材料的性能。通过这些力学参数，计算得到复合氧化铝陶瓷的损伤容限从0.389 4 m^1/2提升至0.452 7 m^1/2，提高了16.26%。     

添加聚醚醚酮对Al_2O_3陶瓷组织及性能的影响（英文）

为改善氧化铝陶瓷的耐磨性和耐蚀性,用喷雾造粒的方法将PEEK(聚醚醚酮)加入到由亚微米氧化铝粉末制备的团聚粉中,制备了Al_2O_3陶瓷基复合涂层材料。用扫描电子显微镜分析了复合材料的组织结构,测试了复合陶瓷涂层的耐磨性和耐腐蚀性,并与纯氧化铝的性能进行对比。结果表明:添加PEEK的Al_2O_3复合陶瓷涂层在磨损试验中的摩擦系数低于Al_2O_3陶瓷,摩擦磨损更稳定,耐磨性更高,在20和30 N载荷下,复合涂层的平均摩擦因数分别为0.593 0和0.589 6,降低了15.8%和15.6%,平均磨损量分别降低了15.7%和17.6%;相对于Al_2O_3陶瓷涂层,复合陶瓷涂层的自腐蚀电位提高15.3%,电流密度降低47.5%,耐腐蚀性提高。     

Preparation and characterization of ZTA bioceramics with and without gradient in composition

Properties and proof of suitability of homogeneously and graded ZTA bioceramics with various Y₂O₃ stabilized zirconia contents were investigated. Therefore porous alumina was infiltrated with different amounts of Y₂O₃ doped ZrO₂ precursors. At homogeneously infiltrated samples biaxial flexural strength and wear behavior were investigated (ISO 6474). Subsequently, at hip joint heads the static fracture strength was determined (ISO 7206-10). Materials ranging from approx. 4 to 20 wt% Y₂O₃ stabilized zirconia were characterized relative to the sinter density, the microstructure, the phase composition and the dispersion of the stabilized zirconia phase. Bioceramics showed high sinter density, fine microstructures, excellent wear property and significantly increased biaxial flexural strength. A 41% increase in strength through the formation of Y₂O₃ stabilized zirconia gradient in the conical bore of the heads was reached. Low compressive stresses in cone of this heads were found.ZTA bioceramics are potentially suitable for use as hip replacement components.     

Extrusion-based additive manufacturing of functionally graded ceramics

The Ceramic On-Demand Extrusion (CODE) process has been recently proposed for additive manufacturing of dense, strong ceramic components via extrusion with uniform layered drying. This study focuses on enabling CODE to fabricate functionally graded ceramics. A controlled volumetric flowrate for each ceramic paste was used to achieve a gradient between alumina and zirconia. A dynamic mixer was built to mix constituent ceramic pastes homogeneously. Functionally graded alumina/zirconia samples were printed, sintered, and tested to examine the capability of CODE in fabricating functionally graded components. The desired and actual material compositions were compared using energy dispersive spectroscopy. Dimensions of sintered samples were evaluated to study the deformation of functionally graded components during drying and sintering. Vickers hardness was also measured at different locations, corresponding to different material compositions. Finally, a case study was conducted to demonstrate the capability of the proposed method to build functionally graded ceramics with complex geometries.     

Cavitation wear of structural oxide ceramics and selected composite materials

The usage of ceramic materials in the applications endangered by intensive cavitation could limit erosion phenomena. In the presented work, cavitation erosion resistance of commonly used (in structural application), oxide phases (α-alumina, tetragonal zirconia) were investigated. Additionally, the behaviour under cavitation conditions of two composite materials, based on alumina and zirconia matrices, was tested.Significant difference in cavitation wear mechanisms for alumina and tetragonal zirconia materials was observed. Alumina was degraded by removing the whole grains from the large surface subjected to cavitation. Degradation of zirconia proceeded locally, along ribbon-like paths of removed grains. Cavitation wear of composites was strongly dependent on the residual stress state in the material. Alumina/zirconia composite with compressive stresses in the matrix showed a significant improvement of cavitation resistance. The zirconia/tungsten carbide composite with relatively high level of tensile stresses in the matrix was the worst of all investigated materials.     

Preparation of interpenetrating alumina–copper composites

To prepare interpenetrating alumina–copper composites, alumina foams were activated with titanium coating by chemical vapor deposition and then were infiltrated with molten copper by expendable casting process. The microstructure and phase composition of the composites were analyzed, and bending strength, electrical conductivity, friction and wear properties were tested. The results showed that the bonding between ceramic and metal was fine in the composites while no reactions took place between them because of the undissolved titanium coating. With increase of ceramic fraction, the electrical conductivity of the composite decreased, whereas the bending strength increased. The composite failure occurred by ductile fracture of the metal followed by fracture of the ceramic. The wear rate of the composites decreased with increase of ceramic fraction. And the wear of the composites was featured with ceramic struts peeling compared with ploughing and adhering wear for pure copper.     

Graded Casting of Materials with Continuous Gradients

A process is introduced for producing continuously graded materials by slip casting with a continuous flow of slip of changing composition. The approach has been tested using alumina and zirconia slips to produce alumina/zirconia composites with a graded composition. Observation of the microstructure has shown that the phases are relatively well dispersed. Compositional analysis revealed a relatively smooth transition in composition through the thickness of sintered bodies. Results have also indicated that for flow rates up to ∼ 60 cm/min, the highest linear flow rate tested, the casting rate of alumina slips containing 38.6 vol% solids was not affected.     

Zirconia matrix composite dispersed with stainless steel particles: Processing and oxidation behavior

Materials with non uniform properties are being developed to optimize several functions of industrial components in severe atmospheres at high temperature. These composites called M(p)-CMC(s): “ceramic matrix composites dispersed with metal particles” are candidates for high-temperature structure materials as functionally graded materials (FGMs) such as intermediate components between electrolyte and interconnecting components in SOFC.Preparation of a model composite M(p)-CMC(s) is described. Powder metallurgy process is used to obtain a dense composite (98% of the theoretical density) based on yttrium stabilized zirconia for the ceramic part and on 304L stainless steel for the metallic part. The characteristics of this material as well as its behavior under oxidation at high temperature are reported.     

Thermal residual stress gradients in an alumina–zirconia composite obtained by electrophoretic deposition

In order to understand the mechanical behavior of layered composites with compositional gradient, it is necessary to determine their state of residual stresses. Compositionally graded materials can offer the advantage of eliminating abrupt changes in composition between layers having different thermal expansion coefficient. The existence of a compositional gradient can reduce discontinuities in thermal residual stresses, something beneficial from the point of view of the mechanical properties.We present here a study of the microstructure and state of residual stressses in a layered material made of homogeneous layers of alumina and alumina–zirconia separated by thin (less than 300 μm) intermediate compositionally graded layers. The composite was obtained by controlled deposition of powders from solution using an electrophoretic deposition (EPD) method. The phase distribution and compositional gradient in the sintered composite were investigated using scanning electron microscopy (SEM). Thermal residual stresses generated during cooling after sintering were measured by using fluorescence ruby luminiscence piezo-spectroscopy and the profile of hydrostatic stress on alumina was determined at steps of about 300 μm along the direction of the compositional gradient, and at steps of about 30 μm in the compositionally graded layers. The obtained profile of hydrostatic stresses on alumina grains follows closely the profile of compositional changes along the layered composite. The presence of thin intermediate graded layers reduce significantly changes in stress in the layered composite.     

Alumina/zirconia ceramic membranes fabricated by temperature induced forming technique

It is well known that the fabrication technique of porous ceramic composites has a significant effect on their microstructure and properties. In the present study, alumina/zirconia ceramic composites doped with magnesia were fabricated by temperature induced forming technique using tri-ammonium citrate and polyacrylic acid (PAA) as dispersant and gelling agents, respectively. The zirconia content was up to 20 wt% and added at the expense of alumina while the magnesia content was up to 2 wt% over the total mass. The optimum amount of ammonium citrate tribasic needed for dispersing the ceramic slurry was determined by measuring zeta potential of slurries. The prepared green alumina/zirconia composites were subjected for solid state sintering at 1550 °C for 1 h. The densification parameters, phase composition, average pore diameter, microstructure and cold crushing strength of sintered alumina/zirconia ceramics were investigated by the suitable techniques. The results revealed that the addition of tri-ammonium citrate to ceramic slurries enhanced the zeta potential which reached ?28.3 mV by adding 1 wt.-%. The bulk density was decreased while the apparent porosity was increased with the increase of zirconia content. The apparent porosities of sintered porous composites were in the range of 38.8–48.5%. The average pore diameter for the composite containing 15% zirconia was 1.79 μm and pore volume was 0.11 ml/g. The obtained microstructure exhibited zirconia grains located on the grain boundaries of Al₂O₃ matrix. The existence of zirconia in addition to magnesia hindered the growth and deformation of the matrix. The cold crushing strength of porous composites was decreased from 16.0 to 8.5 to MPa by increasing the zirconia content from 5 to 20 wt.-%.