Mechanical,electrical, and thermal expansion properties of carbon nanotube-based silver and silver-palladium alloy composites

The mechanical, electrical, and thermal expansion properties of carbon nanotube (CNT)-based silver and silver-palladium (10:1, w/w) alloy nanocomposites are reported. To tailor the properties of silver, CNTs were incorporated into a silver matrix by a modified molecular level-mixing process. CNTs interact weakly with silver because of their non-reactive nature and lack of mutual solubility. Therefore, palladium was utilized as an alloying element to improve interfacial adhesion. Comparative microstructural characterizations and property evaluations of the nanocomposites were performed. The structural characterizations revealed that decorated type-CNTs were dispersed, embedded, and anchored into the silver matrix. The experimental results indicated that the modification of the silver and silver-palladium nanocomposite with CNT resulted in increases in the hardness and Young’s modulus along with concomitant decreases in the electrical conductivity and the coefficient of thermal expansion (CTE). The hardness and Young’s modulus of the nanocomposites were increased by 30%–40% whereas the CTE was decreased to 50%–60% of the CTE of silver. The significantly improved CTE and the mechanical properties of the CNT-reinforced silver and silver-palladium nanocomposites are correlated with the intriguing properties of CNTs and with good interfacial adhesion between the CNTs and silver as a result of the fabrication process and the contact action of palladium as an alloying element.     

Aluminum matrix composites reinforced by molybdenum-coated carbon nanotubes

To extend the application of carbon nanotubes (CNTs) and explore novel aluminum matrix composites, CNTs were coated by molybdenum layers using metal organic chemical vapor deposition, and then Mo-coated CNT (Mo-CNT)/Al composites were prepared by the combination processes of powder mixing and spark plasma sintering. The influences of powder mixing and Mo-CNT content on the mechanical properties and electrical conductivity of the composites were investigated. The results show that magnetic stirring is better than mechanical milling for mixing the Mo-CNTs and Al powders. The electrical conductivity of the composites decreases with increasing Mo-CNT content. When the Mo-CNT content is 0.5wt%, the tensile strength and hardness of Mo-CNT/Al reach their maximum values. The tensile strength of 0.5wt% Mo-CNT/Al increases by 29.9%, while the electrical conductivity only decreases by 7.1%, relative to sintered pure Al. The phase analysis of Mo-CNT/Al composites reveals that there is no formation of Al carbide in the composites.     

Chemical,mechanical, and thermal expansion properties of a carbon nanotube-reinforced aluminum nanocomposite

In the present study, the chemical and mechanical properties and the thermal expansion of a carbon nanotube (CNT)-based crystalline nano-aluminum (nano Al) composite were reported. The properties of nanocomposites were tailored by incorporating CNTs into the nano Al matrix using a physical mixing method. The elastic moduli and the coefficient of thermal expansion (CTE) of the nanocomposites were also estimated to understand the effects of CNT reinforcement in the Al matrix. Microstructural characterization of the nanocomposite reveals that the CNTs are dispersed and embedded in the Al matrix. The experimental results indicate that the incorporation of CNTs into the nano Al matrix results in the increase in hardness and elastic modulus along with a concomitant decrease in the coefficient of thermal expansion. The hardness and elastic modulus of the nanocomposite increase by 21% and 20%, respectively, upon CNT addition. The CTE of CNT/Al nanocomposite decreases to 70% compared with that of nano Al.     

Tungsten nanoparticle-strengthened copper composite prepared by a sol-gel method and in-situ reaction

Tungsten nanoparticle-strengthened Cu composites were prepared from nanopowder synthesized by a sol-gel method and in-situ hydrogen reduction. The tungsten particles in the Cu matrix were well-dispersed with an average size of approximately 100-200 nm. The addition of nanosized W particles remarkably improves the mechanical properties, while the electrical conductivity did not substantially decrease. The Cu-W composite with 6wt% W has the most comprehensive properties with an ultimate strength of 310 MPa, yield strength of 238 MPa, hardness of HV 108 and electrical conductivity of 90% IACS. The enhanced mechanical property and only a small loss of electrical conductivity demonstrate the potential of this new strategy to prepare W nanoparticle-strengthened Cu composites.     

Mechanical properties and friction behaviors of CNT/AlSi<Subscript>10</Subscript>Mg composites produced by spark plasma sintering

The mechanical properties and friction behaviors of CNT/AlSi₁₀Mg composites produced by spark plasma sintering (SPS) were investigated. The results showed that the densities of the sintered composites gradually increased with increasing sintering temperature and that the highest microhardness and compressive strength were achieved in the specimen sintered at 450℃. CNTs dispersed uniformly in the AlSi₁₀Mg matrix when the addition of CNTs was less than 1.5wt%. However, when the addition of CNTs exceeded 1.5wt%, the aggregation of CNTs was clearly observed. Moreover, the mechanical properties (including the densities, compressive strength, and microhardness) of the composites changed with CNT content and reached a maximum value when the CNT content was 1.5wt%. Meanwhile, the minimum average friction coefficient and wear rate of the CNT/AlSi₁₀Mg composites were obtained with 1.0wt% CNTs.     

Mechanical properties and friction behaviors of CNT/AlSi_(10)Mg composites produced by spark plasma sintering

The mechanical properties and friction behaviors of CNT/AlSi_(10)Mg composites produced by spark plasma sintering(SPS) were investigated.The results showed that the densities of the sintered composites gradually increased with increasing sintering temperature and that the highest microhardness and compressive strength were achieved in the specimen sintered at 450°C.CNTs dispersed uniformly in the AlSi_(10)Mg matrix when the addition of CNTs was less than 1.5wt%.However,when the addition of CNTs exceeded 1.5wt%,the aggregation of CNTs was clearly observed.Moreover,the mechanical properties(including the densities,compressive strength,and microhardness) of the composites changed with CNT content and reached a maximum value when the CNT content was 1.5wt%.Meanwhile,the minimum average friction coefficient and wear rate of the CNT/AlSi_(10)Mg composites were obtained with 1.0wt% CNTs.     

Development of non-shrinkable ceramic composites for use in high-power microwave tubes

Al_2O_3–CaO–SiC-based ceramic composites with four different compositions were sintered at 1700℃ for 3 h in an air furnace. The phase analysis, microstructural characterization, and elemental composition determination of the developed composites were performed by X-ray diffraction(XRD), field-emission scanning electron microscopy(FESEM), and energy-dispersive X-ray(EDAX) analysis, respectively. The shrinkage, thermal properties, and electrical resistivity of the composites were also studied. The experimental results showed the effects of adding silicon carbide and calcia to alumina on the thermal, electrical, and shrinkage properties of the resultant composites. Among the four investigated ceramic composites, the one composed of 99 wt% alumina, 0.5 wt% CaO, and 0.5 wt% SiC exhibited the best characteristics for use as a potting material in a dispenser cathode of a microwave tube. The material exhibited slight expansion instead of shrinkage during drying or firing. Other properties of the composite powder, such as its thermal properties and electrical resistivity, were comparable to those of a commercial alumina powder.     

Review of metal matrix composites with high thermal conductivity for thermal management applications

Metal matrix composites with high thermal conductivity and tailorable coefficient of thermal expansion are found widespread applications in electronic package and thermal management.The latest advances in manufacturing process,thermal properties and brazing technology of SiC/metal,carbon/metal and diamond/metal composites were presented.Key factors controlling the thermo-physical properties were discussed in detail.The problems involved in the fabrication and the brazing of these composites were elucidat...     

Fabrication and thermal conductivity of copper matrix composites reinforced by tungsten-coated carbon nanotubes

Carbon nanotubes (CNTs) were coated by tungsten using metal organic chemical vapor deposition. Magnetic stirring was employed to disperse the W-coated CNTs (W-CNTs) in a Cu matrix, and then, the mixed powders were consolidated by spark plasma sintering. The W-CNTs obtained a uniform dispersion within the Cu matrix when the W-CNT content was less than 5.0vol%, but high content of W-CNTs (10vol%) resulted in the presence of clusters. The W-CNT/Cu composites containing low content of W-CNTs (<5.0vol%) exhibited a higher thermal conductivity than the sintered pure Cu, while the CNT/Cu composites exhibited no increase in thermal conductivity after the incorporation of uncoated CNTs. The W-CNT content was found to play a crucial role in determining the thermal conductivity of the W-CNT/Cu composites. The thermal conductivity of the W-CNT/Cu composites increased first and then decreased with the W-CNT content increasing. When the W-CNT content was 2.5vol%, the W-CNT/Cu composite obtained the maximum value of thermal conductivity. The thermal resistance of the (W-CNT)-Cu interface was predicted in terms of Maxwell-Garnett effective medium approximation, and its calculated value was about 3.0×10-9 m2·K·W-1.     

Mechanical and thermal properties of AA7075/TiO2/Fly ash hybrid composites obtained by hot forging

In the present paper, multiple reinforcements TiO2 and fly ash were utilized for the fabrication of AA7075 matrix based hybrid composites using stir casting technique followed by hot forging. In hybrid composites, the fly ash content was fixed to 3 wt% while that of TiO2 was varied from 2.5 to 10 wt%. Scanning electron microscopy images revealed homogenous dispersion of both the reinforcements in AA7075 matrix.Compression test was conducted to study the mechanical behaviour of hybrid composites. The hybrid composites showed increase in compressive strength with the incorporation of multiple reinforcements and further increased with the increase in the weight fractions of TiO2 particles. The coefficient of thermal expansion was measured between 50 and 250 ℃ with a high precision thermal mechanical analyser. The thermal coefficient of hybrid composites decreased with the addition of TiO2 and fly ash. However a slight decrease in thermal conductivity of hybrid composites was observed when compared to that of AA7075 alloy.     

Enhanced performance of nano-sized SiC reinforced Al metal matrix nanocomposites synthesized through microwave sintering and hot extrusion techniques

In the present study, nano-sized SiC (0, 0.3, 0.5, 1.0 and 1.5 vol%) reinforced aluminum (Al) metal matrix composites were fabricated by microwave sintering and hot extrusion techniques. The structural (XRD, SEM), mechanical (nanoindentation, compression, tensile) and thermal properties (co-efficient of thermal expansion- CTE) of the developed Al-SiC nanocomposites were studied. The SEM/EDS mapping images show a homogeneous distribution of SiC nanoparticles into the Al matrix. A significant increase in the strength (compressive and tensile) of the Al-SiC nanocomposites with the addition of SiC content is observed. However, it is noticed that the ductility of Al-SiC nanocomposites decreases with increasing volume fraction of SiC. The thermal analysis indicates that CTE of Al-SiC nanocomposites decreases with the progressive addition of hard SiC nanoparticles. Overall, hot extruded Al 1.5 vol% SiC nanocomposites exhibited the best mechanical and thermal performance as compared to the other developed Al-SiC nanocomposites.     

Mechanical properties and friction behaviors of CNT/AlSi10Mg composites produced by spark plasma sintering

The mechanical properties and friction behaviors of CNT/AlSi10Mg composites produced by spark plasma sintering (SPS) were investigated.The results showed that the densities of the sintered composites gradually increased with increasing sintering temperature and that the highest microhardness and compressive strength were achieved in the specimen sintered at 450℃.CNTs dispersed uniformly in the AlSi10Mg matrix when the addition of CNTs was less than 1.5wt％.However,when the addition of CNTs exceeded 1.5wt％,the aggregation of CNTs was clearly observed.Moreover,the mechanical properties (including the densities,compressive strength,and microhardness) of the composites changed with CNT content and reached a maximum value when the CNT content was 1.5wt％.Meanwhile,the minimum average friction coefficient and wear rate of the CNT/AlSi10Mg composites were obtained with 1.0wt％ CNTs.     

二次烧成对CaO-B2O3-SiO2系微晶玻璃结构和性能的影响

研究一次和二次烧成对CaO-B2O3-SiO2(CBS)微晶玻璃的烧结性能与介电性能的影响。用X线衍射(XRD)、扫描电镜(SEM)等分析探讨二次烧成对CBS微晶玻璃的微观结构与介电性能的关系。结果表明:与一次烧成相比,二次烧成能够促进玻璃体中的小晶粒生长,试样的收缩率和体积密度有所增加,有利于介电常数提高和介质损耗的降低,且体系中没有出现新的晶相;875℃烧结的试样,X/Y轴收缩率均为14.33%,体积密度达到2.46 g/cm3,10MHz介电常数和损耗相应为6.21和3.5×10-3,热膨胀系数为11.86×10-6/℃,抗折强度为157.36MPa。     

镀钨碳纳米管增强铜基复合材料的制备及性能

采用羰基热分解法对多壁碳纳米管表面进行镀钨处理,并以镀钨碳纳米管和电解铜粉为原料,进行机械球磨混粉和放电等离子体烧结,制备了镀钨碳纳米管/铜基复合材料.采用场发射扫描电镜观察了粉体和复合材料的组织形貌,并对复合材料物相进行了X射线衍射分析.探讨了镀钨碳纳米管含量和放电等离子体烧结温度对复合材料致密度、抗拉强度、延伸率和电导率的影响.结果表明,镀钨碳纳米管质量分数为1%和烧结温度为850℃时,复合材料的致密度、抗拉强度和电导率最高.与烧结纯铜相比,复合材料的抗拉强度提高了103.6%,电导率仅降低15.9%.     

反应键合B4C–SiC复合材料的组织和力学性能

Reaction-bonded B₄C–SiC composites are highly promising materials for numerous advanced technological applications. However, their microstructure evolution mechanism remains unclear. Herein, B₄C–SiC composites were fabricated through the Si-melt infiltration process. The influences of the sintering time and the B₄C content on the mechanical properties, microstructure, and phase evolution were investigated. X-ray diffraction results showed the presence of SiC, boron silicon, boron silicon carbide, and boron carbide. Scanning electron microscopy results showed that with the increase in the boron carbide content, the Si content decreased and the unreacted B₄C amount increased when the sintering temperature reached 1650°C and the sintering time reached 1 h. The unreacted B₄C diminished with increasing sintering time and temperature when B₄C content was lower than 35wt%. Further microstructure analysis showed a transition area between B₄C and Si, with the C content marginally higher than in the Si area. This indicates that after the silicon infiltration, the diffusion mechanism was the primary sintering mechanism of the composites. As the diffusion process progressed, the hardness increased. The maximum values of the Vickers hardness, flexural strength, and fracture toughness of the reaction-bonded B₄C–SiC ceramic composite with 12wt% B₄C content sintered at 1600°C for 0.5 h were about HV 2400, 330 MPa, and 5.2 MPa·m0.5, respectively.     

粉末冶金制备的AISI 8620钢渗碳后的磨损和力学性能

The effect of carburization on the tensile strength and wear resistance of AISI 8620 steel produced via powder metallurgy was investigated. Alloys 1 and 2 (with 0.2wt% C and 0.25wt% C, respectively) were first pressed at 700 MPa and then sintered at 1300, 1400, or 1500°C for 1 h. The ideal sintering temperature of 1400°C was determined. Afterward, Alloys 1 and 2 sintered at 1400°C were carburized at 925°C for 4 h. The microstructure characterization of alloys was performed via optical microscopy and scanning electron microscopy. The mechanical and wear behavior of carburized and noncarburized alloys were investigated via hardness, tensile, and wear tests. After carburization, the ultimate tensile strength of Alloys 1 and 2 increased to 134.4% and 138.1%, respectively. However, the elongation rate of Alloys 1 and 2 decreased to 62.6% and 64.7%, respectively. The wear depth values of Alloy 2 under noncarburized and carburized conditions and a load of 30 N were 231.2 and 100.1 μm, respectively. Oxidative wear changed to abrasive wear when the load transitioned from 15 to 30 N.     

磷酸钙/氧化锆复合陶瓷的微观结构及力学性能

利用冷等静压成形, 经不同的温度烧结制备了不同比例的磷酸钙与钇稳定四方氧化锆系列复合陶瓷, XRD、 SEM及力学性能测试结果表明, 随磷酸钙含量的增加, 陶瓷的相对密度降低, 晶粒尺寸变大, 四方氧化锆(t-ZrO2)减少, 单斜氧化锆(m-ZrO2)增加, 导致力学性能下降; 1 350 ℃烧结含磷酸钙质量分数为12％~15％的样品及1 400 ℃烧结含磷酸钙质量分数为15％的样品以t-ZrO2为主, 并含有少量m-ZrO2和TCP(Ca3(PO4)2), 其相对密度大于95％, 综合力学性能评价分析表明, 它可用于CAD/CAM加工口腔修复材料.      

碳纤维增强碳化硅复合材料的力学性能与界面

以A1N和Y2O3为烧结助剂,采用先驱体转化-热压烧结的方法制备了Cf／SiC复合材料．研究了烧结温度对复合材料界面和力学性能的影响及烧结助剂对显微结构的影响．结果表明由于烧结时晶界液相和SiC-A1N固溶体的形成,当烧结温度为1750℃时,复合材料具有较高的致密度和较好的力学性能;当烧结温度升为1800℃时,在复合材料密度增大的同时,其力学性能也大幅度提高,此时复合材料抗弯强度与断裂韧性分别高达691.6MPa和20.7MPa·m1/2,复合材料呈现韧性断裂;进一步提高烧结温度至1850℃时,虽然复合材料的密度有所增加,但由于纤维,基体界面结合过强以及纤维本身性能退化加剧,复合材料呈现典型的脆性断裂,其力学性能急剧降低;纤维／基体的界面是导致纤维增强陶瓷基复合材料性能的关键因素,其中,纤维的脱粘与拔出是主要的增韧因素．     

Effects of BN content on the mechanical properties of nanocrystalline 3Y-TZP/Al2O3/BN dental ceramics

3Y-TZP/3wt％ Al2O3 powder was coated with varying amounts of BN using the urea and borate reaction sintering method, and then multiphase ceramics were prepared by hot pressing sintering. The micro-topography and the compositional analysis of synthesized ceramics were conducted through scanning electron microscopy, transmission electron microscopy and X-ray diffraction. A mechanical tester was used to analyze the Vickers hardness, fracture toughness, and bending strength of the synthesized ceramics. The results showed that the ceramic with a BN content of 12wt％ showed the best processability, but had diminished mechanical properties (such as fracture toughness and bending strength). The ceramic with a BN content of 9wt％ showed better processability than those with 3wt％ and 6wt％ BN. However, the fracture toughness was affected by the addition of 9wt％ BN, making this ceramic only usable as a base material for a three-unit fixed bridge. In con-trast, the ceramics with a BN content of 3wt％ or 6wt％ fulfilled the criteria for use in multi-unit restoration, but their low processability made them unsuitable for milling after sintering.