Blast performance of layered charges enveloped by aluminum powder/rubber composites in confined spaces

A layered charge composed of the JH-2 explosive enveloped by a thick-walled cylindrical casing(active aluminum/rubber and inert lithium fluoride/rubber composites) was designed and explosion experiments were conducted in a 1.3 m3tank and a 113 m3bunker.The blast parameters,including the quasistatic pressure(ΔpQS),special impulse(I),and peak overpressure(Δpmax),and images of the explosion process were recorded,and the influence of the Al content(30% and 50%) and Al particle size(1,10,and 50 μm) on the energy release of aluminum/rubber composites were investigated.The results revealed that the use of an active layer increased the peak overpressure generated by the primary blast wave,as well as the quasistatic pressure and special impulse related to fuel burning within tens of milliseconds after detonation.When the Al content was increased from 30% to 50%,the increases of ΔpQS and I were not obvious,and Δpmaxeven decreased,possibly because of decreased combustion efficiency and greater absorption of the blast wave energy for layers with 50% Al.Compared with the pure JH-2charge,the charge with 1 μm Al particles produced the highest Δpmax,indicating that better transient blast performance was generated by smaller Al particles.However,the charge with 10 μm Al particles showed the largest ΔpQSand I,suggesting that a stronger destructive effect occurred over a longer duration for charges that contained moderate 10 μm Al.

Process−microstructure−properties relationship in Al−CNTs−Al2O3 nanocomposites manufactured by hybrid powder metallurgy and microwave sintering process

Al−2CNTs−xAl2O3 nanocomposites were manufactured by a hybrid powder metallurgy and microwave sintering process.The correlation between process-induced microstructural features and the material properties including physical and mechanical properties as well as ultrasonic parameters was measured.It was found that physical properties including densification and physical dimensional changes were closely associated with the morphology and particle size of nanocomposite powders.The maximum density was obtained by extensive particle refinement at milling time longer than 8 h and Al2O3 content of 10 wt.%.Mechanical properties were controlled by Al2O3 content,dispersion of nano reinforcements and grain size.The optimum hardness and strength properties were achieved through incorporation of 10 wt.%Al2O3 and homogenous dispersion of CNTs and Al2O3 nanoparticles(NPs)at 12 h of milling which resulted in the formation of high density of dislocations and extensive grain size refinement.Also both longitudinal and shear velocities and attenuation increase linearly by increasing Al2O3 content and milling time.The variation of ultrasonic velocity and attenuation was attributed to the degree of dispersion of CNTs and Al2O3 and also less inter-particle spacing in the matrix.The larger Al2O3 content and more homogenous dispersion of CNTs and Al2O3 NPs at longer milling time exerted higher velocity and attenuation of ultrasonic wave.

Preparation and properties of graphene nanoplatelets reinforced aluminum composites

5.0 vol.% graphene nanoplatelets(GNPs) and aluminum powders were mixed to prepare GNPs/Al composites via high-energy ball milling(HEBM). The mixed powders were subjected to spark plasma sintering(SPS) and subsequent hot extrusion. The microstructure and mechanical properties of extruded composites were investigated by X-ray photoelectron spectroscopy(XPS), transmission electron microscopy(TEM) and tensile tests. In the extruded composites, 5.0 vol.% GNPs were dispersed homogeneously and no serious GNP-Al interfacial reaction occurred. As a result, the yield strength and ultimate tensile strength of the extruded GNPs/Al composites reached 462 and 479 MPa, which were 62% and 60% higher than those of the extruded Al matrix, respectively. The enhanced mechanical properties were attributed to the effective load transfer capacity of dispersed GNPs. This demonstrated that it may be promising to introduce dispersed high-content GNPs via HEBM, SPS and hot extrusion techniques and GNP-Al interfacial reaction can be controlled.

Microstructural and mechanical behavior of blended powder semisolid formed Al7075/B_4C composites under different experimental conditions

This work aimed to fabricate B4C reinforced aluminum matrix composites via blended powder semisolid forming that is an implementation of the benefits of semisolid forming to the powder metallurgy. Al7075 elements were incrementally added to ethanol solution under mechanical mixing. Al7075 constituents and B4C particles were blended in a high energy ball mill. Cold compacted Al7075/B4C blends were pressed at semisolid state. The effects of the size of the matrix（20, 45 and 63 μm）, reinforcing volume fraction（5%, 10% and 20%） and semisolid compaction pressure（50 and 100 MPa） on the morphology, microstructure, density, hardness, compression and bending strength were thoroughly analyzed. Experimental results revealed that the highest microstructural uniformity was achieved when large B4C particles（45 μm） were distributed within the small particles（20 μm） of the matrix phase. Composites with matrix particles larger than reinforcing phase indicated agglomerations in loadings more than 10%（volume fraction）. Agglomerated regions resisted against penetration of the liquid phase to the pores and lowered the density and strength of these composites. Composites with 20 μm Al7075 and 20%（volume fraction） 45 μm B4C powder pressed under 100 MPa exhibited the highest values of hardness（HV 190） and compressive strength（336 MPa）.

Microstructure,mechanical and wear properties of aluminum borate whisker reinforced aluminum matrix composites

The microstructural features and the consequent mechanical properties were characterized in aluminium borate whisker(ABOw)(5, 10 and 15 wt.%) reinforced commercially-pure aluminium composites fabricated by conventional powder metallurgy technique. The aluminium powder and the whisker were effectively blended by a semi-powder metallurgy method. The blended powder mixtures were cold compacted and sintered at 600 ℃. The sintered composites were characterized for microstructural features by optical microscopy(OM), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), transmission electron microscopy(TEM) and X-ray diffraction(XRD) analysis. Porosity in the composites with variation in ABOw contents was determined. The effect of variation in content of ABOw on mechanical properties, viz. hardness, bending strength and compressive strength of the composites was evaluated. The dry sliding wear behaviour was evaluated at varying sliding distance at constant loads. Maximum flexural strength of 172 MPa and compressive strength of 324 MPa with improved hardness around HV 40.2 are obtained in composite with 10 wt.% ABOw. Further increase in ABOw content deteriorates the properties. A substantial increase in wear resistance is also observed with 10 wt.% ABOw. The excellent combination of mechanical properties of Al-10 wt.%ABOw composites is attributed to good interfacial bonds, less porosity and uniformity in the microstructure.

Microstructure and Tensile Properties of Yttria Coated-Alumina Particulates Reinforced Aluminum Matrix Composites

The liquid-phase coating method was used to deposit Y2O3 ceramic on the surface of α-Al2O3. The coated-Al2O3p/6061AI composites were produced using squeeze casting technology. The microstructure and tensile properties of the composites were analysed and studied. The results showed that the coated AI2O3 particles are able to disperse homogeneously in the aluminum liquid. The microstructure of the composites is more even in comparison with that of as-received powders. The tensile testing indicated that mechanical properties of the coated-AI2O3p/6061AI composites are better than those of uncoated particles. In the composite with 30% volume fraction, the tensile strength, yield strength as well as elongation is increased by 29.8%, 38.4% and 10.3%, respectively. The SEM analysis of fracture indicated that the dimples of the coated-Al2O3p/6061Al composites are more even.

Mechanical properties of aluminum-based nanocomposite reinforced with fullerenes

The strengthening effect of fullerenes in aluminum matrix composites was investigated. The composites are produced using a two-step ball-milling technique combined with a hot rolling process. First, fullerene aggregates, where fullerene molecules initially come together to form giant particles(~200 μm in diameter) via van der Waals bonding, are shattered into smaller particles(~1 μm in diameter) by planetary milling. Second, primarily ball-milled fullerenes are dispersed in aluminum powder via attrition milling. Finally, aluminum/fullerene composite powder is consolidated by hot-rolling at 480 °C. For the composite sheet, grain refinement strengthening and dispersion hardening by fullerenes are accomplished at the same time, thereby exhibiting HV ~222 of Vickers hardness(e.g., ~740 MPa of yield strength) with only 2%(volume fraction) of fullerenes.

Microstructure of Ni–Al powder and Ni–Al composite coatings prepared by twin-wire arc spraying

Ni–Al powder and Ni–Al composite coatings were fabricated by twin-wire arc spraying（TWAS）. The microstructures of Ni-5wt%Al powder and Ni-20wt%Al powder were characterized by scanning electronic microscopy（SEM） and energy dispersive spectroscopy（EDS）. The results showed that the obtained particle size ranged from 5 to 50 μm. The morphology of the Ni–Al powder showed that molten particles were composed of Ni solid solution, NiAl, Ni_3Al, Al_2O_3, and NiO. The Ni–Al phase and a small amount of Al_2O_3 particles changed the composition of the coating. The microstructures of the twin-wire-arc-sprayed Ni–Al composite coatings were characterized by SEM, EDS, X-ray diffraction（XRD）, and transmission electron microscopy（TEM）. The results showed that the main phase of the Ni-5wt%Al coating consisted of Ni solid solution and Ni Al in addition to a small amount of Al_2O_3. The main phase of the Ni-20wt%Al coating mainly consisted of Ni solid solution, Ni Al, and Ni_3Al in addition to a small amount of Al and Al_2O_3, and Ni Al and Ni_3Al intermetallic compounds effectively further improved the final wear property of the coatings. TEM analysis indicated that fine spherical NiAl_3 precipitates and a Ni–Al–O amorphous phase formed in the matrix of the Ni solid solution in the original state.

Preparation of CNT/AlS i10Mg composite powders by high-energy ball milling and their physical properties

This study investigated the effects of carbon nanotube （CNT） concentration on the micro-morphologies and laser absorption proper- ties of CNT/AlSi10Mg composite powders produced by high-energy ball milling. A scanning electron microscope, X-ray diffractometer, laser particle size analyzer, high-temperature synchronous thermal analyzer, and UV/VIS/NIR spectrophotometer were used for the analysis of micro- graphs, phases, granulometric parameters, thermal properties, and laser absorption properties of the composite powders, respectively. The results showed that the powders gradually changed from flake- to granule-like morphology and the average particle size sharply decreased with in- creases in milling rotational speed and milling time. Moreover, a uniform dispersion of CNTs in AlSi10Mg powders was achieved only for a CNT content of 1.5wt%. Laser absorption values of the composite powders were also observed to gradually increase with the increase of CNT concentration, and different spectra displayed characteristic absorption peaks at a wavelength of approximately 826 nm.

Micromechanical simulation and experimental investigation of aluminum-based nanocomposites

Ceramic reinforced metal matrix nanocomposites are widely used in aerospace and auto industries due to their enhanced mechanical and physical properties.In this research,we investigate the mechanical properties of aluminum/Nano-silica composites through experiments and simulations.Aluminum/Nanosilica composite samples with different weight percentages of silica nanoparticles are prepared via powder metallurgy.In this method,Nano-silica and aluminum powders are mixed and compressed in a mold,followed by sintering at high temperatures.Uniaxial tensile testing of the nanocomposite samples shows that adding one percent of Nano-silica causes a considerable increase in mechanical properties of nanocomposite compared to pure aluminum.A computational micromechanical model,based on a representative volume element of aluminum/silica nanocomposite,is developed in a commercial finite element software.The model employs an elastoplastic material model along with a ductile damage model for aluminum matrix and linear elastic model for nano-silica particles.Via careful determination of model parameters from the experimental results of pure aluminum samples prepared by powder metallurgy,the proposed computational model has shown satisfactory agreement with experiments.The validated computational model can be used to perform a parametric study to optimize the microstructure of nanocomposite for enhanced mechanical properties.

3D printed aluminum matrix composites with well-defined ordered structures of shear-induced aligned carbon fibers

Carbon fiber reinforced aluminum composites with ordered architectures of shear-induced aligned carbon fibers were fabricated by 3D printing.The microstructures of the printed and sintered samples and mechanical properties of the composites were investigated.Carbon fibers and aluminum powder were bonded together with resin.The spatial arrangement of the carbon fibers was fixed in the aluminum matrix by shear-induced alignment in the3D printing process.As a result,the elongation of the composites with a parallel arrangement of aligned fibers and the impact toughness of the composites with an orthogonal arrangement were 0.82%and 0.41 J/cm^(2),respectively,about 0.4 and 0.8 times higher than that of the random arrangement.

Study on the Physical and Mechanical Properties of Al-Powder Reinforced Bioactive Glass: Ceramic Composite Material

Glass-ceramic samples, having composition of SiO2-35, CaO-45, Na2O-10 and P2O5-10 in weight ratio were prepared through sintering route. Glass powder was reinforced by Al powder. The strength of glass-ceramic composite was found to be temperature dependent, and it varies with the addition of Al powder. Flexural strength increases with the increase of powder addition and sintering temperature, however, decreases with the increase of sintering time. There is an optimum temperature (>1100℃) above which flexural strength of all samples decreases. Bulk density changes to a higher value as the addition of Al-powder increases up to 3% by weight above which density decreases slowly. On the other hand, apparent porosity and water absorption decrease with the increase of percentage of Al powder added. Porosity and water absorption also showed a dependent characteristic on sintering time and sintering temperature.

Microstructural characterization and mechanical properties of friction surfaced AA2024-Ag composites

The effects of Ag on the microstructure, mechanical properties, and electrical conductivity of AA2024 aluminum alloy coating were investigated. It was fabricated by friction surfacing as an additive manufacturing process. To carry out this investigation, Ag was added by 5.3, 10.6, and 16.0 wt.% to an AA2024 consumable rod by inserting holes in it. It was found that due to the strengthening by solid solution and the formation of precipitates and intermetallic containing Ag, the driving force for grain growth is reduced and consequently the grain size of the coating is decreased. After artificial aging heat treatment, the electrical conductivities of the coatings containing 0 and 16.0 wt.% Ag are increased by 4.15%(IACS) and decreased by 2.15%(IACS), respectively. While considering a linear relationship, it can be proposed that for a 1 wt.% Ag increase, the strength and hardness of the coating will be increased by 1.8% and 1.0%, respectively. It was established that the effect of Al6(Cu,Ag)Mg4 precipitate formation on strengthening is greater than that of Ag-rich intermetallic.

Exploration of Al-based matrix composites reinforced by hierarchically spherical agents

Al-based composites reinforced with A1-Ti intermetallic compounds/Ti metal hierarchically spherical agents were successfully fabricated by powder metallurgy. This kind of structure produces strongly bonded interfaces as well as soft/hard/soft transition regions between the matrix and reinforced agents, which are beneficial to load transfer during deformation. As expected, the resultant composites exhibit promising mechanical properties at ambient temperature. The underlying mechanism was also discussed in this paper.

Phase Composition Analysis of TiN-AI_2O_3Synthesized from Aluminum-containing Dross and Rutile by Aluminothermic Reductionnitridation Method

TiN- Al2O3 composite powder was prepared by aluminothermic reduction- nitridation method with starting materials of aluminum-containing dross and rutile,and metallic aluminum in the aluminum-containing dross as reducer. The influences of synthesis temperature（600-1 400 ℃） and aluminum-containing dross addition（20% lower than theoretical value,theoretical value,20% higher than theoretical value,and 50% higher than theoretical value） on phase compositions and microstructure of the composites were investigated,and the reaction mechanism was analyzed. The results show that（1） TiN- Al2O3 composite powder can be synthesized under the experimental conditions; the main phases are TiN,α-Al2O3,a little bytownite,and MgAl2O4;（2）enhancing synthesis temperature or increasing aluminumcontaining dross addition favors the reaction of aluminothermic reduction- nitridation;（3） in the synthesized products,α-Al2O3 is platy or columnar; TiN is sub-micron granular,which reinforces and toughens the composite.

Mechanical Properties of a Low-thermal-expansion Aluminum/Silicon Composite Produced by Powder Metallurgy

AI matrix composite containing high volume fraction silicon has been promising candidate for lightweight and low-thermal-expansion components. Whereas, optimization of its mechanical properties still is an open challenge. In this article, a flexile powder metallurgy processing was used to produce a fully dense AI-4.0Cu （wt%） alloy composite reinforced with 65 vol.% Si particles. In this composite, Si particles were homogenously distributed, and the particle size was refined to the range of 3-15 μm. Tensile and flexural strength of the composite were 282 and 455 MPa, respectively, about 100% and 50% higher than the best properties reported in literature. The measured fracture toughness of the composite was 4.90 MPa m1/2. The improved strength of 65%Si/AI was attributed to the optimized particle characteristics and matrix properties. This investigation is expected to provide a primary understanding of the mechanical behaviors of Si/AI composites, and also promote the structural applications of this low-thermal-expansion material.

建筑铝合金模板的表面改性与耐蚀耐磨性能研究

为了提升建筑铝合金模板的表面耐蚀性和耐磨性,在6061铝合金模板表面制备了聚氨酯/Al(Ni基非晶合金)涂层,研究了Ni基非晶合金粉替代Al粉比例对复合涂层表面形貌、截面形貌、硬度、耐磨性和耐蚀性的影响。结果表明:随着Ni基非晶合金粉替代率的升高,复合涂层表面孔洞数量减少,孔洞等缺陷所占面积分数有所减小,不同Ni基非晶合金粉体积分数的复合涂层的厚度都约为125μm。在涂层中加入Ni基非晶合金粉后,复合涂层的显微硬度、耐磨性有不同程度提高,与基体的结合强度有不同程度减小,且随着复合涂层中Ni基非晶合金粉体积分数的增加,复合涂层的显微硬度逐渐增大,与基体的结合强度和磨损率逐渐减小。添加Ni基非晶合金粉的复合涂层的腐蚀速率都小于未添加Ni基非晶合金粉的T0涂层,且Ni基非晶合金粉体积分数为45%的复合涂层具有较高的硬度、耐磨性及最佳耐蚀性能。

激光粉末床熔融成形金刚石增强铝基复合材料

添加质量分数3%金刚石颗粒并利用激光粉末床熔融技术制备6061铝基复合材料。采用光学显微镜、扫描电子显微镜、X射线衍射仪、电子密度计、电子式万能试验机对3%金刚石/6061铝基复合材料的微观组织、相对密度和拉伸性能进行了表征与分析。结果表明:金刚石与Al基体反应生成了针状Al4C3相,并沉积在α-Al基体上,导致晶界位错密度增加,强度提高,抗失效能力增强。金刚石的添加促使6061铝基体中热裂纹消失,但存在孔洞缺陷。较低的扫描速度增加了激光光斑与被加工材料接触的时间,导致金刚石颗粒部分石墨化,铝基体部分蒸发,进而形成内部缺陷,降低了复合材料的相对密度(97%)。金刚石的加入显著提高了激光粉末床熔融技术成形金刚石/6061铝基复合材料的抗拉强度,当激光功率为350 W、扫描速度为800 mm·s-1时,复合材料的极限抗拉强度达到最大值244.2 MPa,屈服强度211.6 MPa,伸长率2.1%。

粉末冶金(SiCp+B_(4)C)/6061Al复合材料组织与性能研究

采用热等静压工艺制备了体积分数为40%的(SiCp+B4C)/6061Al复合材料,研究固溶时效处理对40%(SiCp+B_(4)C)/6061Al复合材料显微组织、热导率、线膨胀系数、力学性能和微屈服强度的影响。结果表明:热等静压法制备的铝基复合材料组织致密;热等静压态复合材料的平均线膨胀系数为13.1×10^(-6) K^(-1),热导率为165.3 W/(m·K);固溶时效态复合材料的平均线膨胀系数为13×10^(-6) K^(-1),热导率为146.4 W/(m·K);与热等静压态相比,固溶时效态复合材料的抗拉强度提高了88%,为477 MPa,抗弯强度为644 MPa,微屈服强度为236 MPa,具有较高的力学性能和尺寸稳定性。本文采用的材料设计方法与热等静压成形技术,为高品质高体积分数颗粒增强铝基复合材料低成本制造提供基础。

颗粒增强铝基复合材料热等静压近净成形有限元模拟

目的建立可靠的模拟方法,以更高效地预测颗粒增强铝基复合材料(PRAMC)粉末热等静压中的形状变化和不同部位致密度的差异,解决传统实验试错方法适用性差且费时费力的问题,满足批量应用的需求。方法以45%(体积分数)SiCp/6092Al复合材料为研究对象,构建了能预测粉末热等静压成形过程的有限元模型。使用Gurson-Tvergard-Needleman(GTN)模型作为粉末本构模型,建立了粉末尺度的代表性体积单元(RVE)对GTN模型进行修正。结果通过对比GTN模型计算结果与实验结果,发现修正后的GTN模型能更准确地预测模型的最终变形尺寸,与修正前相比,相对误差降低了1.6%~2.9%。使用修正后的GTN模型对杯形回转体零件的热等静压成形过程进行预测,最终形状的计算结果与实验结果的相对误差仅为0.2%~3.1%,致密度分布的相对误差在0.5%以内。在探究包套厚度对热等静压过程的影响时发现,随着包套厚度的增大,热等静压过程中的屏蔽作用增强,内部粉体致密度下降。结论为PRAMC热等静压近终形制备的形状和致密度控制问题提供了有限元预测工具,辅助优化了热等静压工艺和包套设计,降低了颗粒增强铝基复合材料热等静压近净成形过程开发的试错成本。