Thermal and mechanical properties of porous Y-PSZ/zircon composites

 The thermal and mechanical properties of sintered porous composites of yttria-partially-stabilized-zirconia (Y-PSZ) and zircon (ZrSiO₄) were investigated for a broad range of compositions. Fracture strengths of these composites were significantly improved with the zircon addition (0 to 50wt%). The addition of zircon also improved the thermal shock resistance. Specimens sintered at 1500^oC for 6 h with 15–20% porosity were shown to have superior strength and thermal shock resistance. These findings have been used in the manufacturing of ceramic permanent molds for brass casting. Received: 5 December 1997 / Accepted: 13 December 1997     

高温热处理对C/C-SiC复合材料制备与力学性能的影响

以针刺整体炭毡为坯体,采用树脂浸渍和化学气相沉积混合法制备C/C多孔体,然后熔硅浸渗制得C/C-S iC复合材料;研究了C/C多孔体的高温热处理对C/C-S iC复合材料密度、孔隙度、力学性能及断裂方式的影响。结果表明:炭涂层进行高温热处理可改变复合材料的弯曲断裂方式,使其具有一定的“假塑性”,弯曲强度下降约16%,压缩强度提高约20%,硬度增加;C/C多孔体的最终高温热处理可打开孔隙,有利于液S i的渗入,制备出密度较高(>2.0 g.cm-3)、开孔率较小(<4%)的复合材料,但导致其力学性能下降,基本上不影响其断裂方式。     

Effect of coal tar pitch modified by sulfur as a binder on the mechanical and tribological properties of bronze-impregnated carbon-matrix composites

Bronze-impregnated carbon-matrix composites were prepared through compression molding, carbonization and impregnation. The mechanism of sulfuration was studied, and the effect of coal tar pitch modified by sulfur as a binder on the mechanical and tribological properties of composites was investigated by varying the content of sulfur. The results showed that the sulfur addition increased the softening point, carbon yield and C/H atomic ratio of coal tar pitch but decreased the toluene solubility and quinoline solubility due to the dehydrogenating polymerization of pitch molecules. The micro-hardness, bending strength and compressive strength of the composites were enhanced by increasing the mass percentage of sulfur and reached a maximum of 160 HV, 132.82 MPa and 293 MPa at 7 wt. % of sulfur, respectively. However, both the hardness and strength of the composites decreased as the content of sulfur increased beyond 7 wt. %. The friction coefficient value of composites increased monotonously, but the wear rate decreased with increasing sulfur content; subsequently, the wear rate reached a minimum of 3.045 × 10⁻⁷ mm³/Nm at 7 wt. % of sulfur and then ascended. The wear mechanisms of the composites were adhesive wear, abrasive wear and oxidative wear. However, adhesive wear and oxidative wear occurred slightly for the composites with the binder modified by sulfur.     

C/C-SiC复合材料模压成型工艺与性能研究

利用碳纤维编织布为增强体,采用混合粉料模压成型工艺制备C/C-SiC复合材料,分析了各个因素对C/C-SiC复合材料密度及强度影响的大小以及显著性。研究表明,树脂与石墨粉比例和纤维含量对C/C-SiC复合材料密度的影响比较大,而硅粉含量以及配比浓度的影响较小且基本相同;同时树脂与石墨粉比例这一因素对C/C-SiC复合材料强度影响也非常显著。并且随着树脂含量的减少,C/C-SiC复合材料强度降低。     

A study on microstructure and mechanical properties of Al 6061-TiB2 in-situ composites

In situ reinforced aluminium based metal matrix composites (AMMCs) are emerging as one of the most promising alternatives for eliminating the inherent defects associated with ex situ reinforced AMMCs. Researchers in recent past have attempted various processing techniques for the development of in-situ composites, of which liquid metallurgy is the most widely adopted technique. Development of in-situ composites via liquid metallurgy route using master alloys is a relatively new processing technique. Very little information is available providing the usage value of these reinforcing materials.The present study is an attempt to explore the processing and characterization of in situ AMMCs using master alloys as reinforcement materials. Al 6061-TiB₂ in-situ composites were fabricated by liquid metallurgy route using Al 6061 as the matrix material and Al-10%Ti and Al-3%B as reactive reinforcements. Tests carried out on the fabricated composites include XRD, metallographic studies, EDAX analysis, microhardness, grain size analysis and tensile strength tests. The developed composites exhibited superior structural properties when compared with base alloy.     

Microstructure and mechanical properties of titanium carbonitride whisker reinforced β-sialon matrix composites

The microstructure, hardness, fracture toughness and thermal shock resistance were investigated for 15 vol.% TiC_0.3N_0.7 whisker reinforced β-sialon (Si_6−zAl_zO₂N_8−z with z=0.6) composites with additions of three different volume fractions 2, 5 and 20 vol.%, of an yttrium-containing glass oxynitride phase. The composites were prepared by hot pressing at 1750°C for 90 min under a uniaxial pressure of 30 MPa in nitrogen atmosphere. The TiC_0.3N_0.7 whiskers were found to survive without deteriorating in morphology or reacting with the β-sialon matrix and/or the glass phase. The TiC_0.3N_0.7 whiskers had no obvious influence on the matrix microstructure, but their presence improved both the hardness and the fracture toughness of the composites. The highest hardness was obtained for the whisker composite with 2 vol.% glass phase (H_v=18.6 GPa). The fracture toughness and thermal shock resistance improved with increasing glass content. The whisker reinforced composite containing 20 vol.% glass showed the highest fracture toughness (K_1C=6.8 MPa m^1/2). No unstable crack extension occurred during the thermal shock test of the obtained composites in the temperature interval 90-700°C, but above 700°C severe oxidation of the whiskers precludes further evaluation of thermal shock properties by the indentation-quench method applied.     

RCLD工艺制备Cf/C、Cf/C-SiC复合材料的氧化性和力学性能

以碳毡为增强体，碳氢有机液体为前驱体，采用自行设计的快速化学液相沉积工艺（RCLD）制备了Cf/C、Cf/C-SiC复合材料；研究了不同密度的毡体和不同的沉积时间等因素对复合材料力学性能和氧化性的影响，根据材料结构特征分析了其影响机理．     

短纤维增强C/C-SiC复合材料的微观结构与力学性能EI北大核心CSCD

综合原料的热物理性能分析和配比设计,实现了C/C复合材料载体孔隙体积的精细控制,采用热压-熔渗两步法在低温条件下制备了具有高致密、低残余Si含量特征的短碳纤维增强C/C-SiC复合材料。系统解析了C/C-SiC复合材料成型过程中的结构演变行为,研究了短纤维增强C/C-SiC复合材料的力学性能和失效机制。结果表明:多孔C/C复合材料载体孔隙的孔径呈双极分布特征,添加芳纶纤维可提高网络孔隙结构的连通性,具有显著的孔隙结构调控作用。SiC基体以网络骨架形态分布于C/C-SiC复合材料内部,与纤维束形成了强界面结合钉扎结构,高含量纤维协同作用下使C/C-SiC复合材料具有优异的综合力学性能,添加芳纶纤维可明显增加复合材料内部裂纹扩展路径,提高C/C-SiC复合材料的断裂韧性。碳纤维的面内各向同性分布及陶瓷相层间均匀分布对C/C-SiC复合材料承载、摩擦稳定性提升均具有积极作用。     

Experimental investigation of the mechanical properties of polymer mortars with nanoparticles

The present paper examines the mechanical properties of polymer mortar (PM), with different weight fraction of nano-Al₂O₃ and nano-Fe₂O₃. The results showed that flexural and compressive strength measured of PM filled with nanoparticles were lower than plain polymer mortar but a considerably stiffness increase was observed for all formulations tested.     

熔融硅液相浸渍法制备C/C-SiC复合材料

采用熔融硅液相浸渍法制备了C/C-SiC复合材料,反应生成的SiC主要分布在层间孔和束间孔碳基体表面,少量分布在束内孔.1600℃渗硅2 h,硅化深度约为2～4 μm.由于液态硅与碳之间的润湿性很好,在碳基体表面形成了连续的SiC层,局部有粗大的多面碳化硅颗粒生成;讨论了细晶粒连续SiC层和SiC粗晶粒形成机理.由于SiC的加入,材料的抗氧化性能得到明显改善.     

Fabrication and mechanical properties of Cu-coatedwoven carbon fibers reinforced aluminum alloy composite

Cu-coatedwoven carbon fibers/aluminum alloy composite (C_f/Al) was prepared by spark plasma sintering. Microstructure and mechanical properties of the composite were investigated. Microstructure observation indicates that the interface reaction is evidently inhibited by Cu coating. Woven carbon fibers are adhered to the matrix alloy by anchor locking effect of matrix alloy immersing into the interstices between carbon fibers. Under the quasi-static and dynamic compressive conditions, the composite exhibits excellent ductility even when the strain reaches 0.8. Adding carbon fibers into ZL205A alloy has no obvious influence on compressive flow stress of the composite. The compressive true stress–true strain curves show that the composite is a strain rate insensitive material. During the tensile tests, the elongation of the composite shows a sharp increase from 4.5% to 13.5% due to the adding of woven carbon fibers. Meanwhile, the tensile strength of the composite is increased slightly from 168 MPa to 202 MPa compared to that of ZL205A alloy. The good ductility of the composite is ascribed to the cracks deflection, fibers pulling out, debonding and breakage mechanisms.     

Sublimation epitaxy of 3C-SiC grown at Si- and C-rich conditions

3C-SiC layers have been grown by using sublimation epitaxy at a source temperature of 2000 °C, under vacuum conditions (<10⁻⁵ mbar) on well oriented (on-axis) 6H-SiC (0001) substrates. Close space sublimation growth geometry has been used in a RF-heated furnace employing high-purity graphite crucible with a possibility to change the growth environment from Si vapor-rich to C vapor-rich. The optical microscopy in transmission mode reveals continuous 3C-domains for 3C-SiC with less than 0.4% 6H-inclusions for the layer grown at Si-rich conditions, and separate 3C-SiC domains for the layer grown at C-rich conditions. The type of 6H-inclusions for layers with continuous domain structure investigated by Atomic Force Microscopy (AFM) is discussed. 2Theta-omega scan shows 0006 and 111 peaks coming from the substrate and the layer, respectively with a higher intensity of the 111 peak for 3C-SiC grown at Si-rich conditions which is related with the continuous character of the 3C-SiC domains.     

Effects of particle size and distribution on the mechanical properties of SiC reinforced Al-Cu alloy composites

This paper studied the combined effects of particle size and distribution on the mechanical properties of the SiC particle reinforced Al-Cu alloy composites. It has been shown that small ratio between matrix/reinforcement particle sizes resulted in more uniform distribution of the SiC particles in the matrix. The SiC particles distributed more uniformly in the matrix with increasing in mixing time. It has also been shown that homogenous distribution of the SiC particles resulted in higher yield strength, ultimate tensile strength and elongation. Yield strength and ultimate tensile strength of the composite reinforced by 4.7 μm sized SiC particles are higher than those of composite reinforced by 77 μm sized SiC particles, while the elongation shows opposite trend with yield strength and ultimate tensile strength. Fracture surface observations showed that the dominant fracture mechanism of the composites with small SiC particle size (4.7 μm) is ductile fracture of the matrix, accompanied by the “pull-out” of the particles from the matrix, while the dominant fracture mechanism of the composites with large SiC particle size (77 μm) is ductile fracture of the matrix, accompanied by the SiC particle fracture.     

Preparation and properties of unidirectional boron nitride fibre reinforced boron nitride matrix composites via precursor infiltration and pyrolysis route

The unidirectional boron nitride fibre reinforced boron nitride matrix (BN_f/BN) composites were prepared via the precursor infiltration and pyrolysis (PIP) route, and the structure, composition, mechanical and dielectric properties were studied. The composites have a high content and fine crystallinity of BN. The density is 1.60 g cm⁻³ with a low open porosity of 4.66%. The composites display good mechanical properties with the average flexural strength, elastic modulus and fracture toughness being 53.8 MPa, 20.8 GPa and 6.88 MPa m^1/2, respectively. Lots of long fibres pull-out from the fracture surface, suggesting a good fibre/matrix interface. As temperature increases, both of the flexural strength and elastic modulus exhibit a decreasing trend, with the lowest values being 36.2 MPa and 8.6 GPa at 1000 °C, respectively. The desirable residual ratios of the flexural strength and elastic modulus at 1000 °C are 67.3% and 41.3%, respectively. The composites have excellent dielectric properties, with the average dielectric constant and loss tangent being 3.07 and 0.0044 at 2-18 GHz, respectively.     

树脂浸渍法对炭/炭复合材料力学性能的影响

将炭纤维坯体CVD增密至不同密度,再对其进行树脂浸渍。对自制样品与英国Dunlop公司和美国Ben dix公司产品的力学性能特征进行了对比分析。结果表明:自制样的抗压强度和抗弯强度远远高于国外样品,层间剪切强度也比国外样品高;自制样品在ρCVD不超过1.45g cm3的情况下,随样品中CVD炭含量的增加,样品的抗弯强度和层间剪切强度值都随之增大,抗弯模量在ρCVD为1.06g cm3时达到最大值。同时用扫描电镜(SEM)分析了这几组试样的弯曲与剪切断口,发现除纯浸渍的样品具有明显的脆性断裂特征外,其余材料都呈假塑性断裂,且强度较高,说明树脂由于炭化后产生的树脂炭与纤维粘结太强,不适合在样品增密的初始阶段作浸渍剂。     

三维机织C/C-SiC复合材料弹性性能预测

试验研究了三维机织C/C-SiC复合材料的弹性性能, 基于复合材料的扫描电镜(SEM)照片, 分析了材料的细观结构的特点, 并提出了一系列的假设, 建立了三维机织C/C-SiC复合材料的细观力学模型, 利用均匀化方法预测了复合材料的弹性常数, 分析了材料的弹性性能随经纱倾斜角的变化规律。结果表明: 预测结果与试验结果吻合较好, 表明该预测模型和方法的正确性; 随着经纱倾斜角的增加, 经纱方向的弹性模量降低, 其它方向的弹性模量均增大, 但面内剪切模量和厚度方向的弹性模量增幅很小。      

Effect of liquid-forming additives on the sintering and mechanical properties of Al2O3/3Y-TZP (30 vol.%) composite

Al₂O₃/3Y-TZP (30 vol.%) composite was pressurelessly sintered with addition of TiO₂MnO₂ and/or CaOAl₂O₃SiO₂ glass. It was found that TiO₂MnO₂ addition greatly enhanced the densification of the composite by the formation of a low-viscosity liquid at sintering temperature. In contrast, the high-viscosity liquid formed by CaOAl₂O₃SiO₂ glass improved mechanical properties because of its repressing effect on grain growth. The composite could be obtained at a temperature as low as 1400°C by co-doping with TiO₂MnO₂ and CAS glass. Bending strength of 552±64 MPa and fracture toughness of 6.03±0.22 MPa m^1/2 were obtained with a doping level of 2 wt.% TiO₂MnO₂ and 2 wt.% CAS glass.     

Effect of alumina particles loading on the mechanical properties of light-cured dental resin composites

The purpose of this study is to evaluate the effect of alumina (Al₂O₃) loading on the mechanical properties of dental resin composites (DRCs). The DRCs were prepared based on Al₂O₃ particles and bisphenol A-glycidyl methacrylate (Bis-GMA) was used as the base monomer. The silane-treated Al₂O₃ particles were mixed with the resin matrix in proportions of 40, 50, and 60 wt%, respectively. Resin matrix without filler was used as the control sample. The Vickers hardness (HV) and flexural modulus (FM) of the DRCs mixed with Al₂O₃ particles were found to be superior compared to the control sample; the values increased from 14.4 to 23.5 kg/mm² and 1.5 to 5.7 GPa, respectively. However, the flexural strength (FS) values of DRCs were slightly decreased as the filler loading increased i.e. from 84.5 to 74.2 MPa. The results also revealed statistically significant increases in the HV and FM. On the other hand, FS values showed significant decrease when filler loading was increased (P < 0.05).     

Processing, microstructure and mechanical properties of nickel particles embedded aluminium matrix composite

Nickel particles were embedded into an Al matrix by friction stir processing (FSP) to produce metal particle reinforced composite. FSP resulted in uniform dispersion of nickel particles with excellent interfacial bonding with the Al matrix and also lead to significant grain refinement of the matrix. The novelty of the process is that the composite was processed in one step without any pretreatment being given to the constituents and no harmful intermetallic formed. The novel feature of the composite is that it shows a three fold increase in the yield strength while appreciable amount of ductility is retained. The hardness also improved significantly. The fracture surface showed a ductile failure mode and also revealed the superior bonding between the particles and the matrix. Electron backscattered diffraction (EBSD) and transmission electron microscopy analysis revealed a dynamically recrystallized equiaxed microstructure. A gradual increase in misorientation from sub-grain to high-angle boundaries is observed from EBSD analysis pointing towards a continuous type dynamic recrystallization mechanism.     

Influence of cobalt phase on thermal shock resistance of Al2O3-TiC composites evaluated by indentation technique

Cobalt-coated Al₂O₃ and TiC powders were prepared using an electroless method to improve resistance to thermal shock. The mixture of cobalt-coated Al₂O₃ and TiC powders (about 70 wt.% Al₂O₃-Co + 30 wt.% TiC-Co) was hot-pressed into an Al₂O₃-TiC-Co composite. The thermal shock properties of the composite were evaluated by indentation technique and compared with the traditional Al₂O₃-TiC composite. The composites containing 3.96 vol.% cobalt exhibited better resistance to crack propagation, cyclic thermal shock and higher critical temperature difference (ΔT_c). The calculation of thermal shock resistance parameters (R parameters) shows that the incorporation of cobalt improves the resistance to thermal shock fracture and thermal shock damage. The thermal physic parameters are changed very little but the flexure strength and fracture toughness of the composites are improved greatly by introducing cobalt into Al₂O₃-TiC (AT) composites. The better thermal shock resistance of the composites should be attributed to the higher flexure strength and fracture toughness.