During the past decade, considerable research effort has been directed towards the development of in situ metal matrix composites (MMCs), in which the reinforcements are formed in situ by exothermal reactions between elements or between elements and compounds. Using this approach, MMCs with a wide range of matrix materials (including aluminum, titanium, copper, nickel and iron), and second-phase particles (including borides, carbides, nitrides, oxides and their mixtures) have been produced. Because of the formation of ultrafine and stable ceramic reinforcements, the in situ MMCs are found to exhibit excellent mechanical properties. In this review article, current development on the fabrication, microstructure and mechanical properties of the composites reinforced with in situ ceramic phases will be addressed. Particular attention is paid to the mechanisms responsible for the formation of in situ reinforcements, and for creep failure of the aluminum-based matrix composites.

One-dimensional carbon nanotubes and two-dimensional graphene nanosheets with unique electrical, mechanical and thermal properties are attractive reinforcements for fabricating light weight, high strength and high performance metal-matrix composites. Rapid advances of nanotechnology in recent years enable the development of advanced metal matrix nanocomposites for structural engineering and functional device applications. This review focuses on the recent development in the synthesis, property characterization and application of aluminum, magnesium, and transition metal-based composites reinforced with carbon nanotubes and graphene nanosheets. These include processing strategies of carbonaceous nanomaterials and their composites, mechanical and tribological responses, corrosion, electrical and thermal properties as well as hydrogen storage and electrocatalytic behaviors. The effects of nanomaterial dispersion in the metal matrix and the formation of interfacial precipitates on these properties are also addressed. Particular attention is paid to the fundamentals and the structure roperty relationships of such novel nanocomposites.

One of the fabrication methods for functionally graded materials (FGMs) is a centrifugal solid-particle method, which is an application of the centrifugal casting technique. However, it is the difficult to fabricate FGMs containing nano-particles by the centrifugal solid-particle method. Recently, we proposed a novel fabrication method, which we have named the centrifugal mixed-powder method, by which we can obtain FGMs containing nano-particles. Using this processing method, Cu-based FGMs containing SiC particles and Al-based FGMs containing TiO2 nano-particles on their surfaces have been fabricated. In this article, the microstructure and mechanical property of Cu/SiC and Al/TiO2 FGMs, fabricated by the centrifugal mixed-powder method are reviewed.

61Complicated interfacial reactions occurred in B4C/6061Al composites.61Reactions involving Mg and Si were divided into oxidation of Mg and other reactions.61Al/B4C reaction produced free B and then activated B/Mg reactions.61B/Mg reactions rather than Mg oxidation were main reasons for Mg consumption.61Interfacial reactions definitely deteriorate age-hardening ability of composites.

For a particle-reinforced composite, strain attribute at both sides of the interface is a critical factor influencing the mechanical properties. Here, we applied transmission electron microscope (TEM) and geometrical phase analysis (GPA) to Ti 5 Si 3 /TiAl composites, and demonstrated that strain compatibility and geometric continuity of these two components primarily relied on interfacial shear deformation. This approach is expected to be applied in other traditional composites for nanoscale strain analysis and performance optimization.

Since the 1960s, it has been a common practice worldwide to pursue a homogeneous distribution of reinforcements within a matrix material, discontinuous metal matrix composites (DMMCs) in particular. Taking an overview of the worldwide activities in DMMC research, despite many favourable attributes such as improved specific strength, stiffness and superior wear resistance, DMMCs with a homogeneous microstructure tend to exhibit a very low room temperature damage tolerance even with a highly ductile matrix material such as aluminium. In this review, a range of uniquely multi-scale hierarchical structures have been successfully designed and fabricated by tailoring reinforcement distribution for DMMCs in order to obtain superior performance. A variety of specific microstructures that were developed in Al, Mg, Cu, Fe, Co and TiAl matrices indicate that there must be adequate plastic regions among the reinforcements to blunt or deflect cracks if one wants to toughen DMMCs. Following this path, aided by theoretical analyses, the most recent success is the design and fabrication of a network distribution of in situ reinforcing TiB whiskers (TiBw) in titanium matrix composites (TMCs), where a tailored three-dimensional (3D) quasi-continuous network microstructure displays significant improvements in mechanical properties. This resolves the brittleness surrounding TMCs fabricated by powder metallurgy. It is the large reinforcement-lean regions that remarkably improve the composite ductility by bearing strain, blunting the crack and decreasing the crack-propagation rate. The fracture, strengthening and toughening mechanisms are comprehensively elucidated in order to further understand the advantages of such an inhomogeneous microstructure, and to justify the development of novel techniques to produce such inhomogeneous microstructures. This approach opens up a new horizon of research and applications of DMMCs and can be easily extended to general multi-phase composites with enhanced physical and mechanical properties.

Nano-SiC particulates (n-SiCp) reinforced Mg-8Al-1Sn (AT81) composites with different volume fractions (0, 0.25, 0.5 and 1.002vol.%) were fabricated by powder metallurgy process (P/M) combined with hot

The aging-hardening kinetics of powder metallurgy processed 2014Al alloy and its composite have been studied. The existence of n-SiC particulates leads to the increase of peak hardness. Interestingly, the aging-hardening peak of the composite takes place at earlier time than that of the unreinforced alloy. Transmission electron microscopy (TEM) studies indicated that the major precipitation phases are Al5Cu2Mn3and θ′ (Al2Cu). Besides, Ω phase appeared in both specimens at peak hardening condition, which has been rarely observed previously in aluminum metal matrix composites without Ag. Accelerated aging kinetics and increased peak hardness may be attributed to the higher dislocation density resulted from the mismatch of coefficients of thermal expansion between n-SiC and 2014Al matrix. The results are beneficial to fabricating high performance composites for the application in automobile field such as pistons, driveshaft tubes, brake rotors, bicycle frames, railroad brakes.

Nano-SiC particulates (n-SiCp) reinforced 2014Al matrix composites with different reinforcement volume fractions (0, 0.25, 0.5 and 1 vol.-%) were fabricated by powder metallurgy combined with hot extrusion. The effect of volume fraction of n-SiCp on mechanical properties of composites was studied at both ambient and elevated temperatures. The increase of n-SiCp content led to an increase in yield strength (YS) and ultimate tensile strength (UTS) and a slight decrease in elongation which is much better than the composites reinforced with micro-SiCp. The 0.5 vol.-% n-SiCp/2014Al composite observed the highest YS and UTS of 090804378 and 090804573 MPa at room temperature and of 090804303 and 090804409 MPa at 473 K. The enhancement of the properties is suggested to be induced by uniformly dispersed and well-bonded n-SiCp reinforcements as well as the age-hardening effect of the more and finer precipitates.

Reinforcing aluminum matrix with much smaller particles, submicron or nano-sized range, is one of the key factor in producing high-performance composites, which yields improved mechanical properties. High-energy ball milling was successfully employed to synthesize nano-crystalline Al7075 alloy powders reinforced with 1, 3 and 5 vol.% Al2O3 at nano-size level. Hot pressing was employed to consolidate the green powder metallurgy products. The nano-composite powders were characterized by SEM, TEM, and XRD. Using Williamson-Hall equation, crystallite size and lattice strain of various Al7075 composite powders were estimated with broadening of XRD peaks. XRD results showed that the crystallite size of aluminum reached 42.30, 36.25 and 32.22 nm, respectively, after 20 h milling in case of Al7075/1, 3, and 5 vol.% Al2O3 nano-composite powder with uniform particle size distribution. TEM observation confirmed the nano-crystalline nature of Al7075/5 vol.% Al2O3 milled powder. Mechanical measurements showed that the hardness and ultimate tensile strength of the Al7075-nano Al2O3 tend to increase with increasing nano Al2O3 volume content at the expense of tensile ductility. (C) 2012 Elsevier B.V. All rights reserved.

A flake powder metallurgy route consists of a slurry based dispersion process and a short time ball milling process was proposed to fabricate strong and ductile CNT/Al composites reinforced with high content CNTs. To improve the interfacial bonding, the CNT/Al nanoflake powders prepared through slurry based dispersion process would go through a short time high energy ball milling process to break native Al 2 O 3 skin and embed CNTs into Al matrix. With the dispersion homogeneity and well-maintained structural integrity of CNTs achieved by the slurry based dispersion, and improvement of interfacial bonding from non-bonding to physical bonding/diffusion assisted bonding and partial reaction bonding through the short time ball milling, an enhancement of tensile strength from 298 to 40662MPa and ductility from 1.9 to 8.8% was obtained for the 262h ball-milled 362vol.% CNT/Al composites, compared to the composites fabricated by sole slurry based dispersion process. It also outperformed that fabricated by direct high energy ball milling, indicating the flake powder metallurgy method could provide a good coordination between the CNT dispersion homogeneity, structural integrity and interfacial bonding.

The uniform dispersion of carbon nanotubes (CNTs) is usually accompanied by severe grain refinement of Al matrix, which leads to the low ductility of CNT/Al alloy composites. To accommodate this dilemma, a flake powder metallurgy route via elemental alloying was proposed to fabricate CNT/Al-Zn-Mg-Cu composites with improved ductility and high strength. CNT/Al flake powders were firstly obtained by ball milling at a low speed to achieve uniform dispersed of CNTs, and then milled with Zn, Mg and Cu elemental flake powders at a high speed to achieve lamellar CNT/Al-Zn-Mg-Cu particles, which were consolidated and homogenized to obtain bulk CNT/Al-Zn-Mg-Cu composites. Compared with the CNT/AA7075 counterparts fabricated by directly using CNTs and atomized AA7075 powders, the CNT/Al-Zn-Mg-Cu composites exhibited improved ductility with high modulus and strength, due to the well-protected and uniformly aligned CNTs, and good dislocation storage capability of the elongated ultrafine grains.

A novel hybrid and multiple-dimensioned ceramic particles (TiB, TiC and Nd 2O 3) reinforced titanium matrix composites were in situ synthesized utilizing the reaction between Ti, C, Nd and B 2O 3 through homogeneously melting in a non-consumable vacuum arc remelting furnace. The thermodynamic of in situ synthesis reaction was analyzed. The phases in the composites were identified by X-ray diffraction (XRD). The microstructures of the composites were observed by means of scanning electron microscopy (SEM), backscattered electron microscopy and second-electron microscopy. Three kinds of reinforcements were found in the titanium matrix: micron-sized TiB whiskers, micron-sized TiC particles and both micron-sized and nano-sized Nd 2O 3 particles. Reinforcements were homogeneously distributed in the matrix. (TiB + TiC + Nd 2O 3)/Ti composites obtained higher mechanical property than TiC/Ti composites.

A range of laminated Ti–TiBw/Ti composites with layer thicknesses of 300μm, 400μm and 500μm were successfully fabricated by reaction hot pressing. The stress–strain curve of the laminated composites with 300μm layer thickness exhibits superior tensile elongation (24.5%) and similar strength compared with the laminated composites with 400μm and 500μm layer thicknesses. The higher elongation is characterized by a prolonged strain softening stage and “non-catastrophic fracture” behavior. The fractography of laminated Ti–TiBw/Ti composites comprises two fracture modes; Ti layers exhibit shear fracture with many shear bands accompanying with micro-voids. However, TiBw/Ti composite layers reveal ductile fracture initiated by nucleation, growth and coalescence of micro-cracks. The difference on fracture mechanisms between Ti layer and TiBw/Ti composite layer is determined by the TiBw reinforcement, while high elongation of the laminated Ti–TiBw/Ti composites with thinner layer thickness is probably attributed to the effective size effect. Meanwhile, with the increase of stress and strain during the plastic deformation process, Ti layer and TiBw/Ti composite layer reveal interaction and mutual competing fracture damage behaviors.

A three-dimensional network-woven architecture made of TiB nanowires has been designed and realized in the matrix of a Ti6Al4V alloy. The architecturally nanostructured design was achieved by dispersing nanoparticles of B 4 C or B onto the surfaces of spherical Ti6Al4V powder particles via mechanical mixing and subsequent consolidation by spark plasma sintering. The as-sintered nanostructured Ti6Al4V-TiB composites demonstrated excellent tensile strengths and ductility that are required for critical applications. The in situ formed TiB nanowires with aspect ratios up to 300 contributed to the high tensile strengths while the architectural design of the TiB nanowires ensured the good tensile ductility.

In this work, Mg matrix composites reinforced with 2.5 wt% nanosized TiB2 particles are fabricated by adding Al-TiB2 master alloy prepared by the chemical reaction of Al-K2TiF6-KBF4 system into molten magnesium. The size distribution of TiB2 particles extracted from the master alloy and their effects on the microstructure and mechanical properties of AZ91 matrix are investigated. The results show that the TiB2 particles display a dominant number of particles less than 100 nm and a uniform distribution in the composites. Also, the grain size of composites is decreased compared with AZ91 alloy. The high resolution TEM reveals that the interface between nanosized TiB2 particles and matrix is clear and bonds well. Besides, the yield strength, ultimate tensile strength and elongation to fracture of composites are improved by 49.4%, 25.5% and 51.1% respectively. Among the strengthening mechanisms of nanosized particles reinforced Mg matrix composites, dislocation strengthening and Orowan strengthening play a more important role in increasing the strength. It is noteworthy that the elongation to fracture of the composites is higher than that of AZ91 matrix, which is contrary to other works.

TiC ceramic particulates locally reinforced aluminum matrix composites were successfully fabricated via self-propagating high-temperature synthesis (SHS) reaction of Al–Ti–C system during aluminum melt casting. The SHS reaction could be initiated when Al contents in the green compacts ranged from 20 wt.% to 40 wt.%. With increasing Al contents, the ignition delay time was prolonged and the adiabatic combustion temperature was lowered. Using XRD and DSC analysis, the SHS reaction characteristic was discussed. The result showed that Al serves not only as a diluent but also as an intermediate reactant participating in the SHS reaction, determining the reaction process and its final producsts. The SEM images revealed a relatively uniform distribution and nearly spherical morphology of TiC particulates in the locally reinforced region, and excellent adhesion and gradient distribution between the TiC particulates reinforced region and Al-matrix. The size of the TiC particulates decreased obviously with increasing Al contents in the blends.

The high mechanical properties of the TiC particle reinforced Al–Cu matrix composites are highly desirable for a wide range of critical applications. However, a long-standing problem for these composites is that they suffer from low ductility and limited formability. Here we fabricated the nano-sized TiC particle reinforced Al–Cu matrix composites by dispersing the nano-sized TiC particles into molten Al–Cu alloy. The tensile strength and ductility were significantly improved with the addition of the nano-sized TiC particles. The tensile strength and elongation of the 0.5wt% nano-sized TiC particle reinforce Al–Cu matrix composite can reach to 540MPa and 19.0%, increased by 11.08% and 187.9% respectively, than those of the Al–Cu matrix alloy (485MPa and 6.6%).

A modified BC route, noted as BC-m, was designed and employed to process an Al g2Si composite in an effort to improve the ductility of the composite. The modification was implemented to improve the effectiveness of particle redistribution of the conventional BC route while maintaining its high grain refinement efficiency. The experimental results demonstrated that route BC-m was strongly effective in redistributing particles while maintaining a comparable microstructural refinement efficiency relative to route BC, which led to an increase in ultimate tensile strength and much higher ductility in the composite. Additionally, the use of route BC resulted in higher yield strength because of its stronger work-hardening effect compared to route BC-m.

以铝基复合材料为代表的金属基复合材料,具有高的比强度、比模量及优异的导热、导电性能,在航空航天、汽车制造、机械电子及其它民用领域具有广泛的应用前景。近年来,碳纳米相作为复合材料的增强体凭借其优异的力学性能和物理性能以及自身结构特点,引起人们极大关注而成为铝基复合材料研究领域的新热点。本文从不同维度结构的碳纳米相(零维碳纳米洋葱、一维碳纳米管、二维石墨烯等)为增强相的角度,概述了这些碳纳米相增强铝基复合材料的制备方法及其在力学性能方面的研究进展,阐述了从单一相增强到多元多维度混杂增强的铝基复合材料在力学性能方面的优势,旨在阐明通过碳纳米相的结构设计和空间构筑实现高强韧性铝基复合材料的设计思路,并展望了高强韧轻金属基复合材料未来的研究趋势。

以铝基复合材料为代表的金属基复合材料,具有高的比强度、比模量及优异的导热、导电性能,在航空航天、汽车制造、机械电子及其它民用领域具有广泛的应用前景。近年来,碳纳米相作为复合材料的增强体凭借其优异的力学性能和物理性能以及自身结构特点,引起人们极大关注而成为铝基复合材料研究领域的新热点。本文从不同维度结构的碳纳米相(零维碳纳米洋葱、一维碳纳米管、二维石墨烯等)为增强相的角度,概述了这些碳纳米相增强铝基复合材料的制备方法及其在力学性能方面的研究进展,阐述了从单一相增强到多元多维度混杂增强的铝基复合材料在力学性能方面的优势,旨在阐明通过碳纳米相的结构设计和空间构筑实现高强韧性铝基复合材料的设计思路,并展望了高强韧轻金属基复合材料未来的研究趋势。

The development of novel nanomaterials brings new opportunity and challenge for high sensing detection of biomolecules. The authors describe the preparation of 3-dimentional hollow graphene balls (3D HGBs) using nickel nanoparticles (Ni-NPs) as the template. The Ni-NPs were synthesized by chemical reduction of nickel chloride and then graphene was coated onto their surface via carburization... [Show full abstract]

O/Al composites. Nanoflake Al powders with native AlO skins were used as building blocks to rapidly assemble into biomimetic nanolaminated structures via compacting and extrusion, giving rise to strong and ductile composites with tensile strength of 26202MPa and plasticity of 22.9%. Thus, it is evidenced that well-balanced strength and ductility can be achieved in biomimetic metal–matrix composites by flake PM.

Laminated composites consisting of alternating layers of TiB w /Ti and Ti(Al) were prepared, and exhibited a superior elongation to fracture that is nearly 20 times higher than that of bulk TiB w /Ti composites. Coupling two- and three-dimensional fracture characterizations of TiB w /Ti-Ti(Al) laminated composites show distinct fracture characteristics including crack distribution, formation of tunnel cracks, and suppression of crack propagation. These experimentally observed fracture characteristics are intimately correlated with in situ monitored strain evolution process, by which we observed that strain localization is effectively suppressed by laminated structure, thus lowering the stress intensity near the crack tip as well as the driving force for crack propagation. As a consequence, laminated composites are not so sensitive to the early cracking, and exhibit a good strength-ductility combination.

Abstract The prospect of extending natural biological design to develop new synthetic ceramic-metal composite materials is examined. Using ice-templating of ceramic suspensions and subsequent metal infiltration, we demonstrate that the concept of ordered hierarchical design can be applied to create fine-scale laminated ceramic-metal (bulk) composites that are inexpensive, lightweight and display exceptional damage-tolerance properties. Specifically, Al(2)O(3)/Al-Si laminates with ceramic contents up to approximately 40 vol% and with lamellae thicknesses down to 10 microm were processed and characterized. These structures achieve an excellent fracture toughness of 40 MPa radicalm at a tensile strength of approximately 300 MPa. Salient toughening mechanisms are described together with further toughening strategies.

The effect of spark plasma sintering (SPS) temperature on the microstructure and mechanical properties of a bulk ultrafine structured Ti 2AlC/TiAl composite prepared by SPS of a mixture of mechanically alloyed Ti–Al powder with a composition of Ti–50Al (at%) and 10 vol% carbon nanotubes (CNTS) has been investigated. X-ray diffraction analysis showed that the sintered bulk material mainly composed of γ-TiAl and Ti 2AlC phases. The microstructures of the samples were examined using scanning electron microscopy and transmission electron microscopy. It was found that when an SPS temperature of 950 °C was used, the bulk Ti 2AlC/TiAl composite had a high density of 98.3%, and a microstructure consisting of a continuous interpenetrating network of Ti 2AlC phase and equiaxed TiAl grains with an average size of 300 nm. The compressive yield strength and hardness of the sintered samples reached 2058 MPa and 6.12 GPa respectively. With increasing the SPS temperature up to 1150 °C, the TiAl grains became significantly coarsened, leading to clearly reduced mechanical properties.

In order to better understand the relationship of structure echanical properties of TiBw/Ti6Al4V (TiBw/Ti64) composites with a network microstructure and deduce the upper limit of TiBw volume fraction, the effects of volume fraction on the microstructure and tensile properties were further investigated. The equation calculating the optimal and maximum volume fractions of reinforcement for the composites with a network microstructure was deduced. For the present system, the optimal and maximum volume fractions were verified to be 5.1vol.% and 10.2vol.%, respectively, by calculation, microstructure observation, tensile properties. When the volume fraction was equal and lower than 5.1vol.%, the coarse TiBw formed, or else, the fine TiBw, the cluster TiBw and the block TiBw, even unhealed pores formed. The tensile strength of TiBw/Ti64 composites increases and then hastily decreases, while the ductility keeps on decreasing with increasing volume fractions of TiBw reinforcement.

金属材料超塑性一般要求具有均匀细小的等轴晶粒,并且在高温超塑变形过程中能够保持晶粒尺寸稳定性,避免晶粒快速长大。轻合金的超塑性不仅要具备等轴细晶组织,还需要通过引入第二相或合金元素等来保证材料的高温组织稳定性,这也是当前金属材料超塑性的研究热点之一。目前提高超塑性材料细晶组织稳定性的策略主要包括：析出第二相粒子钉扎晶界,双相合金的相结构之间抑制彼此生长,复合材料的增强体抑制晶粒长大以及单相合金的溶质原子偏聚等。本文概述了含析出第二相合金、双相合金、金属基复合材料和单相合金等轻合金超塑性组织稳定性的研究现状,并从工业应用需求及降低生产成本的角度,提出了超塑性材料的发展趋势。

金属材料超塑性一般要求具有均匀细小的等轴晶粒,并且在高温超塑变形过程中能够保持晶粒尺寸稳定性,避免晶粒快速长大。轻合金的超塑性不仅要具备等轴细晶组织,还需要通过引入第二相或合金元素等来保证材料的高温组织稳定性,这也是当前金属材料超塑性的研究热点之一。目前提高超塑性材料细晶组织稳定性的策略主要包括：析出第二相粒子钉扎晶界,双相合金的相结构之间抑制彼此生长,复合材料的增强体抑制晶粒长大以及单相合金的溶质原子偏聚等。本文概述了含析出第二相合金、双相合金、金属基复合材料和单相合金等轻合金超塑性组织稳定性的研究现状,并从工业应用需求及降低生产成本的角度,提出了超塑性材料的发展趋势。

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The overall aim of engineering design is to improve on technology and way of life. Here, we show how the tensile properties of magnesium have been improved using concentric alternating macro-ring design. Specifically, Mg-nanoAl 2O 3 layered hybrid nano-composites were fabricated. These nano-composites were then hot extruded into fairly concentric hybrid alternating Mg and Mg-nanoAl 2O 3 macro-ring structures (having stressed micro-interface). We also show the first instance of mechanical property improvement by careful simultaneous design of macrostructure and microstructure in a composite. Here, we focus on the effects of varying the thickness of the pre-extrusion layers. The 0.2%YS, UTS and ductility of the ring structured hybrid nano-composites peaked at 3 mm pre-extrusion layer thickness, where the corresponding properties of monolithic Mg were significantly inferior in comparison. Further, our method of ring structured hybrid composite synthesis may possibly enable significant reduction in time and cost of manufacturing superconducting cables. [All rights reserved Elsevier].

Uniaxial compression tests were carried out on micro-pillars fabricated from nanolaminated graphene (reduced graphene oxide, RGO)-Al composites of different RGO concentrations and laminate orientations (the angle between laminate planes and the pillar axis). It was found that the strengthening capability of RGO can be enhanced by either orienting the RGO layers parallel with the loading direction or raising the RGO concentration. The stress train response of the micro-pillars was populated with discrete bursts, and the stress increments of the bursts scaled with the RGO concentration, regardless of the laminate orientation relative to the loading direction. These observations were interpreted by the variation in the load-bearing capacity of RGO in different laminate orientations, the dislocation annihilation at the RGO/Al interface, and a crack deflection mechanism provided by the robust RGO/Al interface that toughened the composites. This work underscores the importance of structural design and control in the stiffening, strengthening, and toughening of metal matrix composites, and the methodology developed may be applied to other composites with microstructural heterogeneity to probe their specific mechanical behaviors and structure-property correlations.