氮化硅流延膜的制备

流延成型是一种制备高质量陶瓷基片的成型方法.氮化硅是一种高热导率的材料,有望在电子基片领域获得应用.本文利用流延成型制备了具有较好柔韧性和一定强度的氮化硅流延素坯膜.研究了无水乙醇、无水乙醇/丁酮作为溶剂时对浆料粘度的影响.通过优化流延浆料添加剂的各种配比,得出了适合氮化硅粉体(SN-E10)流延的最佳配方.     

烧结温度对含有定向α-Si3N4晶须的Si3N4陶瓷的影响

利用流延成型使α-Si3N4晶须在基体中定向排列,并采用热压烧结技术制备了SGN4陶瓷.用X射线衍射和扫描电镜对陶瓷的物相和显微结构进行了研究,讨论了流延成型对坯体中晶须的分布状态的影响和烧结条件对所得到的块体的显微结构的影响.结果表明:流延成型和热压烧结可以使晶须呈一维定向排布;随着烧结温度的升高,烧结样品的相对密度增大;添加10.6%质量分数)α-Si3N4晶须在1500℃下烧结,Si3N4陶瓷的断裂韧性为9.24MPa·m1/2,Vickers硬度为15.740Pa.在1 600℃α-Si3N4转变成的长柱状β-Si3N4颗粒,大大提高了Si3N4陶瓷的力学性能,其断裂韧性和Vickers硬度分别为10.26MPa·m1/2和16.56GPa.     

晶须含量和取向对Al2O3—SiCw陶瓷刀具材料的增韧特性及切削性能的影响

晶须含量和取向不同将影响到Al_2O_3 SiCw陶瓷刀具材料的力学性能,由此将进一步影响到该刀具材料的切削性能。本文测量了不同晶须含量和不同晶须取向的Al_2O_3-SiCw材料的断裂韧性,分析了晶须含量和晶须取向对该刀具材料增韧效果的影响。试验了不同晶须含量和不同晶须取向的Al_2O_3 SiCw刀具的切削性能。结果表明:晶须含量和取向对刀具材料的磨损和破损有很大的影响。因此在实际应用中应根据刀具损坏方式的不同分别选用不同晶须含量和不同晶须取向的Al_2O_3-SiCw刀具材料。以充分发挥该刀具材料的增韧补强效果。     

电泳法成型超薄陶瓷基片

用于耐高温等苛刻环境下工作的韧性结构陶瓷的研究,推动了复合陶瓷材料的发展,这些材料包括片状陶瓷与陶瓷复合材料、连续增韧纤维陶瓷材料以及功能陶瓷材料。有许多方法制造这些材料,如流延成型、注浆成型、干压成型、离心式注浆成型、轧膜成型,以及等离子体成型和化学蒸镀等。     

低温烧结A／W—ZTA生物活性水基流延膜

为了实现ＺＴＡ材料和ＨＡＰ的同步烧结,必须降低ＺＴＡ材料的烧结温度。选用具有生物活性和较低熔点的Ａ／Ｗ生物微晶玻璃作为ＺＴＡ材料液相烧结的添加剂,利用流延成型工艺,制得了适合流延成型的水基Ａ／Ｗ－ＺＴＡ浆料及流延膜,分析了影响浆料及流延膜的各种因素。在烧结过程中,样品的密度及强度受玻璃添加量的影响,在１３３０℃时,１０ｗｔ％Ａ／Ｗ－ＺＴＡ材料的强度可达３７４ＭＰａ、密度可达９６％。因此在１３３０℃     

高透明耐低温流延聚丙烯包装膜配方工艺研究

采用3层共挤流延成型工艺制备了流延聚丙烯（CPP）薄膜,研究了不同增韧材料对CPP薄膜透明度、雾度及低温落镖冲击质量的影响,并研究了成核剂以及工艺条件对其性能的影响。结果表明,芯层添加10份的聚烯烃弹性体、1.5份的成核剂母料,熔体温度控制在255～265 ℃,冷却辊温度在24 ℃以下时,CPP薄膜的低温韧性好,透明度高、雾度低。     

丙乙无规共聚聚丙烯正压成型杯的雾度与结构的关系

研究了丙乙无规共聚聚丙烯正压成型杯制品的结构演变及其对雾度的影响。结果表明:丙乙无规共聚聚丙烯流延片经过正压成型,内部结构发生了显著变化,晶体经过重新排列组合,分子链方向和片晶组的法线方向从无规分布到沿着施加压力方向取向;流延片外表面存在缺陷,经过正压成型其表面三维结构也发生变化,外表面的凹坑被拉大且变浅,内表面出现起伏和取向条纹结构,外表面存在很多凹坑,对光的散射作用强于内表面,导致外表面雾度高于内表面雾度;内部凝聚态结构从片晶无规分布演变成取向纤维晶结构,使内部雾度降低;流延片表面结构存在缺陷,在正压成型过程中并不会被消除,是影响制品雾度的关键因素。     

影响陶瓷材料流延成型的关键因素

成型是制备功能陶瓷的关键环节，而流延成型技术是制备高性能超薄陶瓷的关键技术。本文对流延成型的流程进行详细介绍，比较了水基流延成型技术与有机流延成型技术的优缺点；在流延成型过程中，浆料制备、流延膜厚度以及流延膜的干燥等因素影响着流延成品的质量，概述了对这些因素作出的要求。     

美杜邦推出PLA用新助剂

美国DuPont（杜邦）公司推出生物降解塑料聚乳酸（PLA）用新助剂BiomaxStrong。 据DuPont公司介绍,这种助剂能提高要求有一定刚性的热成型流延PLA片材的韧性,并降低片材的脆性,改进和提高PLA的抗冲击强度、柔软性和熔体的稳定性。若按BiomaxStrong的推荐用量使用,能提高PLA的抗冲击强度,而对透明性影响很小,PLA仍达到生物降解塑料关于填埋后降解速率的要求。     

陶瓷材料流延成型研究现状

简要概括了陶瓷坯体流延成型的工艺过程,比较了水基流延成型与传统流延成型技术相比的优点和不足之处,着重介绍了陶瓷材料新型流延成型工艺的研究现状,并指出了陶瓷坯体水基流延成型工艺的发展方向。     

Mechanical Properties of Tape-Cast Alumina-Glass Dental Composites

Alumina-glass dental composites were prepared by tape casting and sintering at 1120°C, followed by glass infiltration at 1100°C. Flexural strength and fracture toughness of the composites were investigated in terms of the influence of tape constituents, namely, alumina powder, binder, and plasticizer, on the mechanical properties. Both strength and toughness increased with increasing alumina fraction in tapes and decreased with increasing binder content in binder/plasticizer mixtures. These observations were consistent with the influence of the constituents on mean alumina particle distance in tapes, suggesting that the high strength of glass-infiltrated alumina composites is related to toughening by crack bowing. The strength and fracture toughness of the tape-cast composites, optimized for forming dental crowns, were 508 MPa and 3.1 MPa·m^1/2, respectively, obtained from biaxial tests. Shrinkage of the composites decreased with increasing thermocompression pressure, applied to the tapes prior to sintering, and heating rate to the sintering temperature.     

Processing and Properties of Alumina-Graphite Platelet Composites

Fine-grain Al₂O₃-graphite platelet composites have been fabricated by both filter pressing and tape casting with up to 50 vol% of fine or coarse graphite flakes. Filter pressing behavior remains unchanged with coarse graphite flake additions. Strength of hot-pressed specimens decreases from about 350 to about 50 MPa with 50 vol% graphite. Preliminary experiments indicate that platelet orientation has a significant effect on strength: Platelets oriented perpendicular to the fracture plane and face-on to the crack front are about 20% weaker than composites with platelets oriented both perpendicular to the fracture plane and edge-on to the crack front. This suggests that the flakes behave as oriented voids in the microstructure.     

Fabrication and mechanical properties of laminated HfC–SiC/BN ceramics

Laminated HfC–SiC/BN ceramics were successfully fabricated by tape casting and hot pressing. Fully dense HfC–SiC ultra-high temperature ceramics with homogeneous structure were obtained. The introduction of the weak BN layer resulted in a slight decrease of the flexural strength but significantly improved the fracture toughness compared with monolithic HfC–SiC ceramics. The fracture toughness of laminated HfC–SiC/BN ceramics in the parallel direction peaked at 8.06 ± 0.46 MPa m^1/2, which increased by 115% than that of monolithic HfC–SiC ceramics. The composites showed non-catastrophic fracture behaviors in both parallel and perpendicular directions. It indicates that laminated structure design is a promising approach to obtain full density HfC–SiC ceramics with high fracture toughness.     

Fabrication of laminated SiCw/SiC ceramic composites by CVI

Laminated SiC_w/SiC ceramic composites were prepared by chemical vapor infiltration (CVI) and tape casting, and the advantages of this method were investigated. The results showed that this method can increase strength of the composites by reducing the damage of SiC whiskers and increasing their volume fraction, and increase toughness of the composites by controlling the interfacial bonding between whiskers and matrix and inter-laminar bonding between layers. The volume fraction of whiskers reached 40 vol.%, and the flexural strength, tensile strength and fracture toughness were 315 MPa, 158 MPa and 8.02 MPa m^1/2, respectively. Interfacial and interlaminar crack deflection and bridging were observed.     

Design of crack deflection induced high toughness laminated Si3N4 ceramics based on hollow oriented one-dimensional microstructure

A laminated silicon nitride (Si₃N₄) ceramic material with a hollow, oriented, one-dimensional microstructure was successfully prepared based on the tape casting and sacrificial template method. The results show that hollow, oriented, one-dimensional microstructures can effectively induce crack deflection. Different arrangements of the structural design layer and dense layer will have different effects on the material. In particular, bulks with a single-layer orthogonal arrangement of the structural design layer possess high toughness and obvious crack deflection during the fracture process. A kind of multiscale crack deflection mode was realized. Compared with the fracture toughness of the monolithic Si₃N₄ ceramic bulk (5.55 MPa m^1/2), the fracture toughness can reach 8.73 MPa m^1/2, and the flexural strength can still reach 391.47 MPa with only a slight decrease.     

Determination of mechanical properties of Al2O3/Y-TZP ceramic composites: Influence of testing method and residual stresses

A series of Al₂O₃/Y₂O₃-stabilized zirconia (Y-TZP) ceramic composites with different zirconia contents (5 and 40 vol% Y-TZP) and fabricated by different green processing techniques (a novel tape casting and conventional slip casting) were studied. The microstructure and mechanical properties of the composites were investigated systematically, by means of scanning electron microscopy, Vickers indentation, depth-sensing nanoindentation, and single-edge laser-notched beam (SELNB) techniques. The indentation fracture method was found to be unsuitable for fracture toughness determination in this work. Reliable values of fracture toughness were obtained by the SELNB method with an almost atomically sharp laser-machined initial notch. The microstructure and mechanical properties of the ceramic composites mainly depended on the Y-TZP content. No significant differences were induced by the choice of green processing technique. The contribution of residual stresses to fracture toughness in Al₂O₃/Y-TZP ceramic composites was investigated. To this end, a theoretical model was applied to estimate the increase in fracture toughness due to the measured residual stresses in the samples. It was found that in this case, residual stresses were not the main factor responsible for the toughening in Al₂O₃/Y-TZP composites.     

Processing and properties of ZrB2-SiC composites obtained by aqueous tape casting and hot pressing

ZrB₂-SiC composites with different SiC content were prepared through aqueous tape casting and hot pressing. The influences of dispersant, SiC content and binder content on the rheological properties of slurries were investigated and the conditions for preparing stable ZrB₂-SiC suspensions were optimized. After tape casting and drying, the green ZrB₂-SiC tapes showed good flexibility, lubricious surface and homogeneous microstructure. The ZrB₂ ceramics could be densified to 97.2% after hot-pressing, while the ZrB₂ containing 20 and 30 vol% SiC ceramics were nearly fully densified (>99%). The sintered ZrB₂-20 vol% SiC ceramic had improved mechanical properties compared with ZrB₂ ceramic. Further increase in SiC content resulted in lower flexural strength and fracture toughness. SEM and TEM showed a fine microstructure with a clear grain boundary. The fracture mode changed from intragranular type for ZrB₂ to both intragranular and intergranular type for ZrB₂-SiC composites.     

Multilayered ceramic composites – a review

With the aim of improving the toughness of ceramic materials, laminated composites have been successfully developed since Clegg et al. (1990) inserted weak interfaces using very thin graphite layers between silicon carbide sheets and obtained a composite that exhibited non-catastrophic fracture characteristics. The weak interface must allow the crack to deviate either by deflection or delamination; in other words, the interface must exhibit a fracture resistance that is lower than that of the matrix layer. In parallel, ceramic laminated composites with strong interfaces were developed in which the residual tensile and compressive stresses appeared in alternate layers during cooling after sintering. These composites are prepared by stacking ceramic sheets produced by lamination or tape casting or by the sequential formation of layers by slip casting, centrifugation or electrophoretic deposition. The techniques may be combined to obtain a composite with the most adequate configuration. This work presents a review about the obtainment of multilayered ceramic composites as a toughening mechanism of ceramic plates.     

Mechanical Properties and Fracture Toughness of α-Al2O3-Platelet-Reinforced Y-PSZ Composites at Room and High Temperatures

YPSZ/Al₂O₃-platelet composites were fabricated by conventional and tape-casting techniques followed by sintering and HIPing. The room-temperature fracture toughness increased, from 4.9 MPa·m^1/2 for YPSZ, to 7.9 MPa·m^1/2 (by the ISB method) for 25 mol% Al₂O₃ platelets with aspect ratio = 12. The room-temperature fiexural strength decreased 21% and 30% (from 935 MPa for YPSZ) for platelet contents of 25 vol% and 40 vol%, respectively. Al₂O₃ platelets improved the high-temperature strength (by 110% over YPSZ with 25 vol% platelets at 800°C and by 40% with 40 vol% platelets at 1300°C) and fracture toughness (by 90% at 800°C and 61% at 1300°C with 40 vol% platelets). An amorphous phase at the Al₂O₃-platelet/YPSZ interface limited mechanical property improvement at 1300°C. The influence of platelet alignment was examined by tape casting and laminating the composites. Platelet alignment improved the sintered density by >1% d _th , high-temperature strength by 11% at 800°C and 16% at 1300°C, and fracture toughness by 33% at 1300°C, over random platelet orientation.     

Effect of carbon particle and carbon fiber on the microstructure and mechanical properties of short fiber reinforced reaction bonded silicon carbide composite

Variation of microstructure and mechanical behavior was investigated with the content increase of carbon particles and carbon fiber in the reaction bonded silicon carbide composites. The composites were prepared by slip casting and liquid silicon infiltration. The bulk density is raised with the increase of carbon black due to the formation of fine β-SiC particles. The flexural strength increases for the reduction of residual Si and the formation of SiC framework; whereas a very high carbon content reduces the flexural strength. The fracture toughness is controlled by the contents of carbon particle and carbon fiber. Thus, fiber debonding, fiber pullout and crack deflection are considered as the main toughening mechanisms. Annealing treatment can effectively improve both the flexural strength and fracture toughness. An increase by 49% of fracture toughness is obtained. A series of structural models are proposed to illustrate the structure changes of carbon fiber.