Thermal shock resistance of ZrC matrix ceramics

A ZrC-20 vol% SiC based ceramic matrix composite containing 10 vol% graphite flake was fabricated by hot press sintering. The thermal shock resistance of the materials was investigated through the water-quench method and subsequent three-point bend testing of flexural strength diminution. The ZrC-20 vol% SiC composite containing 10 vol% graphite flake exhibited higher critical temperature difference and higher residual ratio of strength compared with that of ZrC-20 vol% SiC composite. It is the main reason that addition of the graphite flake provides a weak interface into the material which acts to deflect propagating cracks, and the bridging of the cracks occurred. Meanwhile, a laminar structure of the graphite flake would relax the interface stress by sliding of interlayers and provide favorable sites for the dissipation of energy associated with crack growth during fracture.     

Dense sub-micron-sized ZrC-W composite produced by reactive melt infiltration at 1200 °C

ZrC-W composite was produced by reactive infiltration of Zr₂Cu into WC preform at 1200 °C. The WC reacted completely with Zr in the alloy to form 61.8 vol% ZrC and 38.2 vol% W. The infiltrated composite reached a relative density of 98.3% and average grains sizes of about 0.5 μm. The flexural strength and the fracture toughness of the ZrC-W composite was improved by the addition of W.     

SiCP增强泡沫铝基复合材料的制备工艺研究

将SiC颗粒增强铝基复合材料的制备技术与泡沫铝熔体发泡技术相结合,探索了制备SiC颗粒增强泡沫铝基复合材料的工艺方法。讨论了SiC颗粒与铝基体之间存在的润湿性,界面反应以及SiC颗粒在熔体中沉降等问题,通过选择合适的合金成分,对SiC颗粒进行预处理,采用特定的搅拌和发泡等一系列工艺方案成功地予以解决。在熔体发泡过程中,通过严格控制发泡温度、搅拌速度和搅拌时间等工艺参数,制得了孔隙率基本可调,SiC颗粒和孔洞分布均匀的泡沫铝样品。     

Laser cladding of SiC/Si composite coating on Si-SiC ceramic substrates

Pieces of silicon infiltrated silicon carbide (Si-SiC) were coated with a SiC particles reinforced Si matrix composite (SiC/Si) obtained from mixtures of SiC + SiO₂ and SiC + Si by laser cladding. A Nd:YAG pulsed laser delivering an average power of 920 W was used to apply such coatings using the powder blowing technique. The results demonstrate that the use of the SiC + SiO₂ powder mixture produces a severe damage on the base material, whereas the use of the SiC + Si mixture leads to the formation of sound coatings without substrate damage. XRD and nanoindentation measurements corroborate the production of silicon carbides surrounded by a metallic silicon matrix. This method could be used for repairing surface defects of silicon infiltrated silicon carbide ceramics (Si-SiC).     

An investigation on corrosion behaviour of pressure infiltrated Al-Mg alloy/SiCp composites

In this study, effect of Mg alloying addition (2-8 wt.%) on corrosion behaviour of Al matrix composites, in 3.5 wt.% NaCl environment, has been investigated. Composites were produced by pressure infiltration technique at 750 °C and had a SiC particle (SiC_p) volume fraction of ∼60%. Results were evaluated by using potentiodynamic polarisation measurements, immersion tests, SEM, EDS and XRD analysis. Compared to the pure Al matrix, mass loss of the composites decreased with increasing Mg content. Experimental results revealed that intermetallics as a result of reaction between Al-Mg alloy and SiC particle has beneficial effect on corrosion resistance of the composites due to interruption of the continuity of the matrix channels within the pressure infiltrated composites.     

Electrodeposition and characterization of Ni-Co/SiC nanocomposite coatings

Ni-Co/SiC nanocomposite coatings were electrodeposited in a modified watt type of Ni-Co bath containing 20 nm SiC particles to be codeposited. Potentiodynamic polarization tests were conducted to study the effect of the SiC particulates on the electrodeposition of Ni and Co. Scanning electron microscopy was used to assess the morphology of the Ni-Co alloy and Ni-Co/SiC nanocomposite coatings. The distribution of the particulates in the matrix was considered by means of transmission electron microscopy. Applying nanomechanical testing instruments coupled to atomic force microscopy, mechanical properties of the alloy and composite coatings were studied and compared. The presence of 11 vol.% SiC in the Ni-Co matrix increased hardness more than 60%. The average depth of scratch in the mentioned composite coating was about 15% less than that of the Ni-Co alloy coating. The corrosion penetration rate (CPR) of the Ni-Co alloy coating in a 3.5 wt.% NaCl solution was more than 17 times greater than that of the Ni-Co/SiC coating with 30.5 vol.% SiC.     

Processing, microstructure and mechanical properties of magnesium matrix nanocomposites fabricated by semisolid stirring assisted ultrasonic vibration

Particulate reinforced magnesium matrix nanocomposites were fabricated by semisolid stirring assisted ultrasonic vibration. Compared with the as-cast AZ91 alloy, the grain size of matrix alloy in the SiCp/AZ91 nanocomposite stirring for 5 min was significantly decreased due to the addition of SiC nanoparticles. SiC nanoparticles within the grains exhibited homogeneous distribution although some SiC clusters still existed along the grain boundaries in the SiCp/AZ91 nanocomposite stirring for 5 min. With increasing the stirring time, agglomerates of SiC nanoparticles located along the grain boundaries increased. The ultimate tensile strength, yield strength and elongation to fracture of the SiCp/AZ91 nanocomposite stirring for 5 min were simultaneously improved compared with the as-cast AZ91 alloy. However, the ultimate tensile strength and elongation to fracture of the SiCp/AZ91 nanocomposite decreased with increasing the stirring time.     

Effect of particle size and co-deposition technique on hardness and corrosion properties of Ni–Co/SiC composite coatings

Ni–Co/SiC alloy matrix composite coatings were electrodeposited in a modified Watt's bath containing micro and nano sized SiC particles by using conventional electro-co-deposition (CECD) and sediment co-deposition (SCD) techniques. The deposits were characterized using SEM, EDX and XRD analyses, and microhardness and potentiodynamic polarization measurements. The maximum incorporation of the SiC micro- and nano-particles was obtained using the SCD technique at deposition current densities of 2 and 3 A/dm², respectively. It was found that in the composite coatings, incorporation of SiC particles improves the microhardness of unalloyed Ni and Ni–Co alloy matrices. The nanocomposite coatings exhibit higher microhardness values than microcomposite ones. The potentiodynamic polarization measurements in 3.5% NaCl solution revealed that the corrosion resistance of the Ni–Co/SiC nanocomposite coatings is much higher than the Ni–Co alloy and Ni–Co/SiC microcomposite coatings. Moreover, corrosion resistance of Ni–Co/SiC nanocomposite coatings deposited by SCD technique is higher than the ones deposited by CECD technique. Corrosion resistance of the studied Ni–Co/SiC composite coatings was considerably affected by Co content, SiC particle size and content. Hardness enhancement was related to the structural features, and corrosion behavior was discussed based on the formation of corrosion micro cells, diminishing the effective metallic area, and increasing and hindering the corrosion paths.     

Mechanical properties and fractograph of SiC foam-SiC particles-Al composites

A new type of hybrid SiC foam-SiC particles-Al composites used as an electronic packaging substrate material were fabricated by squeeze casting technique. The mechanical properties and the fracture mechanism of the hybrid composites were investigated. The influence of SiC particles and foam hybrid reinforcement on the behavior of the composites was studied. The results show that the interface bonding in the hybrid composites is good for the composites with the unique double interpenetrating structure. The compressive strength of the hybrid composite reinforced by the SiC with the volume fraction of 59.9% is 680 MPa, which is higher than that of any other composites with the same volume fraction of SiC particles reinforcement.     

AZ91镁合金泡沫材料的制备

利用NaCl颗粒作为预制型,采用渗流铸造方法制备了AZ91泡沫合金,样品孔隙之间具有良好的连通性。泡沫密度为0.724g/cm3,孔隙率为0.602。压缩试验结果表明,AZ91镁合金泡沫材料的塑性变形能力明显高于铸态AZ91镁合金。在孔隙被压合的过程中,泡沫材料在低应力条件下发生剪切破坏。这一变形机制在金属泡沫材料中尚未见到报道。     

多孔SiC陶瓷/Zr基非晶合金复合材料动态压缩性能研究

通过压力-浸渗法制备多孔SiC陶瓷/Zr基非晶合金复合材料。利用分离式霍普金森压杆装置(SHPB)、S-4800场发射扫描电镜等测试分析手段,探究复合材料制备保温时间和多孔碳化硅性能对多孔SiC陶瓷/Zr基非晶合金复合材料动态压缩性能的影响,并揭示了其变形机制。结果表明:保温时间和多孔碳化硅性能对多孔SiC陶瓷/Zr基非晶合金复合材料的动态抗压强度都有较大影响,当多孔碳化硅孔隙率为23.77%,平均孔径尺寸为26.72μm时,在复合材料制备浸渗温度为860℃,浸渗后保温6.0 min时,复合材料具有最高的动态抗压强度,为1757 MPa。多孔SiC陶瓷/Zr基非晶合金复合材料动态压缩断裂为脆性断裂,断口微观形貌特征包括SiC陶瓷相上形成具有不同特征的解理台阶,Zr基非晶合金相形成不同形态的脉状花样,非晶相保持相对完整。Zr基非晶合金相能有效阻碍裂纹的扩展,导致非晶相周围的碳化硅碎裂并挤压非晶相整体运动,从而提高了多孔SiC陶瓷/Zr基非晶合金复合材料动态抗压强度。     

SiC泡沫陶瓷增强ZL205A铝合金复合材料的制备与性能研究

本实验通过挤压浸渗工艺成功制备了SiC泡沫陶瓷增强ZL205A铝合金复合材料,并研究了不同孔隙率的泡沫陶瓷增强相对复合材料性能的影响。通过微观结构分析,制备的复合材料两相间结合紧密,没有裂纹及其他缺陷产生。多孔陶瓷作为增强相可以有效地细化ZL205A合金的晶粒,多孔陶瓷孔隙率的降低,孔结构越小,合金晶粒越细小。对制备的复合材料进行力学性能测试,复合材料的硬度和抗弯强度最高能够达到127.6HV和415MPa。对制备的复合材料进行摩擦磨损测试,结果表明,连续陶瓷相的存在将铝基体严重的粘着磨损和剥落磨损转变为较轻的磨粒磨损,极大提升了复合材料的摩擦磨损性能,为其用于耐磨领域提供了理论依据。     

合金元素对SiC/Al双连通复合材料力学性能的影响

采用真空压力浸渗方法制备SiC3D/ZL201A双连通复合材料,借助电子显微镜(SEM)、能谱(EDS)等分析手段,研究合金元素对SiC/Al双连通复合材料组织结构及力学性能的影响。结果表明:SiC3D/ZL201A界面存在Cu、Mg等元素的偏聚,界面组织结构得到改善;合金元素导致SiC3D/ZL201A压缩强度高于SiC3D/纯铝,弯曲强度低于SiC3D/纯铝;SiC3D/ZL201A失效形式主要表现为界面断裂,SiC骨架呈现脆性断裂,铝合金基体呈现韧性撕裂断裂;合金元素产物通过钝化裂纹,改变裂纹扩展方向,桥联等作用提高复合材料的力学性能。     

铸造ZL101A／SiCp复合材料的研究

采用真空搅拌复合工艺制备了铸造ZL101A／SiC复合材料,研究了变质和细化处理对复合材料组织的影响。结果表明：变质和细化处理铸造 ZL101A／SiC复合材料制备工艺的重要处理措施,可明显改善复合材料的组织。利用透射电镜对AL／SiC界面特征及界面反应进行分析,同时对该复合材料的铸造性能（熔体合金流动性能、线收缩、体收缩和热裂倾向）以及力学和物理性能进行了测试。     

Investigation of the microstructure and properties of Al–Si–Mg/SiC composite materials produced by solidification under pressure

Composite materials based on alloys of the Al–Si–Mg system have been obtained via the introduction of 5, 10, and 15 wt % of SiC particles into the alloy melt and the solidification under a pressure. As a result of solidification under pressure, the porosity of the composite materials decreased substantially. An increase in the content of SiC particles in the composites enabled a smaller size of dendritic cells to be obtained. It has been shown by the X-ray diffraction method that, in the process of solidification under pressure, an interaction occurred between the matrix and reinforcing SiC particles. The presence of SiC particles in the structure of composites led to the acceleration of the aging process and to an increase in the peak hardness in comparison with the matrix alloy.     

Investigation on microstructure and mechanical properties of HfB2-SiC-HfC ternary system with different HfC content prepared by spark plasma sintering

HfB₂-based ultrafine composites with 25 vol% SiC and various volume fractions of HfC (5–20 vol%) have been successfully fabricated using spark plasma sintering. The composites were sintered in both 1800 °C and 1850 °C for different soaking times of 5 and 15 min and flexural strength, hardness and fracture toughness of specimens were measured. Sintering mechanism and mechanical properties of composites and HfC impact on them were investigated. The highest relative density (99.97 ± 0.02%) and the lowest apparent porosity (0.07 ± 0.03) were obtained for the specimen with 15 vol% of HfC. This composite also showed the maximum flexural strength (592 ± 17 MPa) and fracture toughness (4.98 ± 0.12 MPam^1/2), even more than the composite with 20 vol% of HfC which had the highest Vickers hardness (22.7 ± 0.9 GPa).     

Friction stir processing of Al/SiC composites fabricated by powder metallurgy

Friction stir processing (FSP) was applied to modify the microstructure of sintered Al–SiC composites with particle concentrations ranging from 4 to 16 vol%. Two SiC particle sizes (490N and 800 grades) were examined. Following FSP, the hardness of the 4 and 8 vol% of 490N grade SiC composites increased from 130 HV and 145 HV to 171 HV and 177 HV respectively. The increase was accounted for by the severe deformation occurring during FSP which uniformly distributed the SiC particles. The composites containing 16 vol% SiC could not be fully consolidated using FSP, and contained residual pores and lack of consolidation which originated from the as-received sintered microstructure. The hardness correlated well with the mean inter-particle spacing for the SiC particles in the case of composites containing 4 and 8 vol% SiC.     

Fabrication of SiC particle dispersed spheroidal graphite cast iron composite by vacuum assisted casting and its microstructure

Abstract

SiC particle preforms were infiltrated with spheroidal graphite cast iron melt by vacuum assisted casting in the sand mould, and spheroidal graphite cast iron composites in which the particles were dispersed in the surface region were fabricated. Although the melt infiltration was not accomplished when the melt was poured under atmospheric pressure, the infiltration was accomplished by the vacuum assisted casting when the SiC particle volume fraction and preform thickness were optimised. When the Si content of the cast iron was 2˙5 mass%, the phase consisting of mainly Fe₃Si was formed at the particle/matrix interface due to the reaction between the cast iron melt and the particles during the infiltration. The matrix of the composite consisted of fine spheroidal graphite particles, ferrite, pearite and chill crystal. Although the increase in the Si content suppressed the reaction and chill, no infiltrated area was observed in the composite.     

Effect of specific pressure on fabrication of 2D-Cf/Al composite by vacuum and pressure infiltration

Carbon fiber reinforced aluminum matrix (C_f/Al) composite has many excellent properties, and it has received more and more attention. Two-dimensional (2D) C_f/Al composites were fabricated by vacuum and pressure infiltration, which was an integrated technique and could provide high vacuum and high infiltration pressure. The effect of specific pressure on the infiltration quality of the obtained composites was comparatively evaluated through microstructure observation. The experimental results show that satisfied C_f/Al composites could be fabricated at the specific pressure of 75 MPa. In this case, the preform was infiltrated much more completely by aluminum alloy liquid, and the residual porosity was seldom found. It is found that the ultimate tensile strength of the obtained C_f/Al composite reached maximum at the specific pressure of 75 MPa, which was improved by 138.9% compared with that of matrix alloy.     

Effects of Y2O3 on SiC/MoSi2 composite by mechanical-assistant combustion synthesis

MoSi₂ based materials are considered as a potential high temperature structural parts. In this work, a 0.5 wt% Y₂O₃–20 vol% SiC/MoSi₂ composite was successfully prepared by pressureless sintering from mechanical-assistant combustion synthesized powders. Adding a small amount of Y₂O₃ to the SiC/MoSi₂ composite decreased the apparent activation energy of sintering by 10.4%, resulting in a denser composite with finer grains. The relative density, flexural strength, Vickers hardness and fracture toughness of 0.5 wt% Y₂O₃–20 vol% SiC/MoSi₂ increased by 5.3%, 27.7%, 27.2% and 35.8% as compared to 20 vol% SiC/MoSi₂, respectively. The oxidation mass gain of Y₂O₃–20 vol% SiC/MoSi₂ at 1200 °C was higher than that of 20 vol% SiC/MoSi₂ for 16.9%, while it still exhibited very good oxidation resistance at this temperature.