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In terms of aluminum alloy matrix composites, the effect of reinforcement on precipitation is worth investigating. In this work, the silicon carbide nanoparticles-reinforced 7075Al (SiCnp/7075Al) composite was fabricated through a series of powder metallurgy procedures, shift-speed ball milling, hot pressing, and hot extrusion, and the precipitation behavior of SiCnp/7075Al composite was compared with that of 7075Al alloy after T6 treatment. The results show that only a small addition (1 vol%) of SiCnp modifies the morphology and dispersion of precipitates. The uniformly dispersed small precipitates (η′ phase) and increased dislocation density have a positive influence on the mechanical properties of composites. Based on the fracture surface and element composition, a fracture mode dominated by precipitated phase-induced crack initiation was proposed. This study suggests a promising approach to design the alloy matrix composites through controlling the behavior of precipitated phases with nano-reinforcement. [ABSTRACT FROM AUTHOR]

The microstructure design of graphene based reinforcement is an effective route to obtain graphene/aluminum composites with good mechanical properties. In this study, alumina anchored on graphene nanosheets hybrid (Al2O3@GNS) was in situ synthesized by a sodium chloride template-assisted high-temperature calcination strategy. Al2O3@GNS was used as a reinforcement to fabricate aluminum matrix composites (Al2O3@GNS/Al) by flake powder metallurgy (FPM) route. It was found that Al2O3@GNS was homogenously distributed and a relatively obvious synergistic strengthening effect was acquired by employing Al2O3@GNS as reinforcement of the composites. ∼1.0 vol%-Al2O3@GNS/Al composite obtained the maximum tensile strength of 359 MPa, an ∼131.6% improvement superior to pure Al. The strengthening efficiency of Al2O3@GNS is higher than those reinforced by individual GNS, Al2O3 or its simple mixture. An elongation of 11.2% was achieved in the ∼ 1.0 vol%-Al2O3@GNS/Al composite, exhibiting a favorable strength-ductility synergy. The synergistic strengthening effect was attributed to the formation of an interlocked network of Al2O3@GNS, which was beneficial to improve the load transfer efficiency from the matrix to reinforcement in the composites. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) reinforced Al composite foams with different CNT contents are fabricated through an improved powder metallurgy approach by combining in-situ chemical vapor deposition (CVD), short time ball-milling, and space-holder method. The CNTs are uniformly dispersed on the surface of Al particles by in-situ CVD process, followed by a short time ball-milling process enabling an excellent interfacial bonding between CNTs and the Al matrix. The pore size and microstructures of the composite foams can be well tailored by the carbamide particle templates. The yield strength and energy absorption capacity of composite foams reach 18.1 MPa and 15.8 MJ m−3 with 3.0 wt% CNT addition, which are ≈1.3 and ≈3.6 times higher than those of pure Al foam, respectively. The energy absorption efficiency of the CNT/Al composite foams achieves a maximum of ≈0.86, when the CNT content is up to 3.0 wt%. Additionally, compressive and energy absorption properties of the CNT/Al composite foams increase with the increment of relative density. The failure mode of the Al foam changes from plastic mode to brittle mode combined with ductile mode, as a result of CNT addition. [ABSTRACT FROM AUTHOR]

In this work, few-layered MoS2 (FLM) nanosheet-reinforced Al matrix composites are developed through powder metallurgy and hot extrusion. The microstructure, mechanical properties, and strengthening mechanisms have been systematically investigated. It is found that Al12Mo and Al2S3 can be formed in-situ during the sintering process, resulting in the improvement of interfacial bonding between FLM and Al matrix. With 1.5 wt.% of FLM addition, an improved tensile strength of 234 MPa with a high elongation of 17% can be obtained. Moreover, the strengthening mechanisms are also demonstrated to be grain refinement, dislocation strengthening, and load transfer, and the calculation indicates that load transfer is the main contribution factor. This work will inspire more new designs of metal matrix composites with balanced strength and ductility. [ABSTRACT FROM AUTHOR]

Highlights • A novel and efficient method to fabricate CNTs reinforced Al alloy matrix composite foams is put forward. • CNTs are homogeneously dispersed in the matrix. • The effects of CNTs on pore structure during foaming process is discussed. Abstract Uniformly dispersed carbon nanotubes (CNTs) reinforced aluminum (Al) alloy matrix composite foams were successfully fabricated by the combination of in-situ chemical vapor deposition and powder metallurgy using titanium hydride as a blowing agent. The effects of CNTs on the pore structure were systematically studied. The results showed that compared to the Al alloy foam, the introduction of CNTs could significantly improve the pore uniformity and reduce the pore size. As a result, the compressive property of composite foam had an obvious increase. The reasons for the enhanced pore structure mainly lie in that the CNTs increased nucleation sites for the decomposed hydrogen and the limited the movements of bubbles in the melt during foaming process. [ABSTRACT FROM AUTHOR]

Abstract: Carbon nanotubes (CNTs) with diverse structures (tubular and herringbone) reinforced Al matrix composites were fabricated by a combination of in situ growth process of CNTs in Al powders and powder metallurgy (PM) process. The enhancement efficiency of CNTs with different structures and the interfacial phenomenon between CNTs and Al matrix were investigated. The results showed that herringbone CNTs with more defects reacted with Al matrix slightly and a thin intermediate layer (Al4C3) of about 1–4nm was formed between herringbone CNTs and Al matrix. Nevertheless, the interface between tubular CNTs and Al matrix was close-knit and no obvious transition layer (new phase) was found. The mechanical performance of the composites indicated that the enhancement efficiency of herringbone CNTs in Al matrix composites was lower than that of tubular CNTs, due to the formation of the brittle intermediate layer of Al4C3, implying that tubular CNTs should be more suitable to reinforce Al matrix composite. [Copyright &y& Elsevier]

Abstract Nano-MgAl 2 O 4 particles and Mg x Al (1-x) B 2 whiskers co-reinforced Al matrix composites were prepared through powder metallurgy and hot working processes, involving ball-milling, cold pressing, sintering, repressing, and hot extrusion. The microstructure, tensile strength and hardness of the composites, the phase composition of the particles and the whiskers, and the interface between the whisker and the aluminum matrix were investigated systemically. The results show that during the hot extrusion, the reinforcements are uniformly distributed in the matrix, and the whiskers are arranged in the direction of extrusion. The whiskers are hexagonal prisms with close-packed hexagonal crystal structure and all the inner angles are 120°. Besides, the whisker elongates along the [0001] crystal orientation, and the six planes of the sidewalls belong to the {10 1 ¯ 0} family of crystal planes. As the content of reinforcement increases, the strength and hardness of the composites increase, while the elongation decreases. The composite contained 25.2 wt% reinforcements has a tensile strength of 400 MPa and a hardness of 124 HV. [ABSTRACT FROM AUTHOR]

This work presents an in-situ chemical vapor deposition (CVD) method to synthesis carbon nanotube (CNT) on Al powders in a vertical tube furnace. The carbon nanotube reinforced Al matrix composites (CNT/Al composites) were fabricated by a new powder metallurgy (PM) approach associated with vacuum induction melting technique. It was shown that CNT was homogenously distributed in the Al matrix, and an interfacial transiting layer of Al 4 C 3 was formed between Al matrix and CNT in the bulk material. The tensile test showed that 1.5 vol% CNT/Al composites exhibited the largest tensile strength of 191 MPa as well as an excellent elongation of 32.6%. The strengthening efficiency of the 1.5 vol% CNT/Al composites improved by ~ 80% compared to the unreinforced pure Al. The strengthening mechanisms were mainly attributed to the load transfer of CNT, Al 4 C 3 and dislocation strengthening. The Al 4 C 3 transiting layer was beneficial to increase the interfacial shear strength and prolong the slide deformation of dislocation by forming an orientation relationship of Al 4 C 3 <001> // Al <111> and CNT (002) // Al 4 C 3 (001) according to the transmission electron microscope (TEM) observation. Besides, the thermocycling measurement enriched and deepened the understanding of the effect of Al 4 C 3 on improving the interfacial bonding, degrading the interfacial thermal mismatch between CNT and the Al matrix and increasing the compactness of the CNT/Al composites. [ABSTRACT FROM AUTHOR]

Graphene nanosheets (GNS) have attracted lots of attention as an ideal reinforcement in Al matrix composites. However, there are still challenges limiting the performance of the composites, such as the homogenous distribution of GNS in Al matrices, the structural integrity of GNS after ball-milling, and the interfacial bonding between GNS and Al matrices. This work presents a new approach to grow GNS on Al powders at 600 °C by in-situ chemical vapor deposition (CVD) process, using methane as the carbon source, and Cu as the catalyst. The GNS coated Cu reinforced Al matrix bulk composites (Cu@GNS/Al) from the composite powders was fabricated by powder metallurgy (PM) technique. It was found that Cu 2+ from CuCl 2 can easily anchor onto the surfaces of Al particles uniformly though a nanoscale-disperse-method in alcohol, enabling the homogenously dispersion of Cu particles in Al matrices after being reduced from Cu 2+ in hydrogen. With the assistance of Cu particles, network-liked GNS was successfully synthesized in-situ and strongly bonded with Al, resulting in a good mechanical performance of the composites. It is indicated that the tensile strength of the composites was improved by ~ 200% compared to the unreinforced pure Al. The strengthening mechanism was mainly ascribed to the load transfer of GNS, precipitation strengthening of Al 2 Cu compounds after 400 °C annealing and dislocation strengthening. [ABSTRACT FROM AUTHOR]

Aiming to develop a new generation of lightweight, high-strength, and heat-resistant structural materials, BNNSs/Al composites were fabricated based on powder metallurgy process. TEM results demonstrated that BNNSs were mainly distributed at grain boundaries, forming BNNSs-AlN-Al transition interface during the sintering process. The Al grains of BNNSs/Al composites maintained stable at temperatures up to 573 K and achieved unprecedented high-temperature tensile strength of about 329 ± 6 MPa. The experimental and simulation results revealed that the reduction of tensile strength of Al matrix at high temperature was due to the decrease of grain boundary stability, which led to grain rotation and stress concentration near grain boundary. However, BNNSs with unique two-dimensional morphology can effectively suppress grain boundary diffusion and grain boundary motion, which retarded the softening of Al grains. More importantly, the strongly bonded BNNSs-AlN-Al transition interface can enhance drag effect of BNNSs, which effectively limits the grain rotation during the high-temperature deformation and stimulates the coordinated intragranular plastic deformation of Al grains. Thus, the BNNSs/Al composite maintained a high level of deformability and efficient load transfer even at 573 K. Our findings provide a promising route to extending the application of Al matrix composites in the field of high-temperature structures. [Display omitted] [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) reinforced Al composite foams were successfully fabricated by the combination of an in-situ chemical vapor deposition (CVD), short-time ball-milling and space-holder method. The CNTs are homogeneously dispersed and embedded in the Al foam matrix after 90 min ball-milling while maintaining the structural integrity. Both compressive properties and energy absorption capacity of the composite foams increase with the increment of CNT content but decrease with the temperature rising between 25 and 250 °C. The compressive yield strength and the plateau stress of 3.0 wt%-CNT/Al composite foams maintain 16.8 and 20.2 MPa at 150 °C, respectively, which are much higher than the corresponding yield stress (5.7 MPa) and plateau stress (8.6 MPa) of the pure Al foam. Especially, the energy absorption capacity of the 3.0 wt%-CNT/Al composite foams reaches 19.8 MJ/m 3 at 150 °C, which is ~2.5 times higher than that of pure Al foam. Fracture analysis shows that the failure mode of the Al foam changes from ductile type to brittle type combined with ductile type, as a result of the CNT addition in the matrix. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) reinforced Al matrix composites were produced by a modified powder metallurgy route, including in-situ synthesis of CNTs on Al powders by chemical vapor deposition and subsequent ball-milling process. The influence of CNT content (0–4.5 wt%) on the microstructure, mechanical and coefficient of thermal expansion (CTE) performance of CNT/Al composites was systematicly investigated. During the fabrication process, well dispersed CNTs with integrated structure are deeply embedded in Al matrix to form an effective interface bonding. The hardness and tensile strength of CNT/Al composites monotonically increase with the increment of CNT content. The 4.5 wt%-CNT/Al composites exhibit largest hardness and tensile strength, which is 2.3 and 2.4 times higher than that of starting Al, respectively. The CTEs of the composites decrease with the increase of CNT content at the temperature range of 100–300 °C. The CTE of the 4.5 wt%-CNT/Al composites reduces as much as 17% compared with that of starting Al at 100 °C. Thus, we offer a large variety of mechanical and CTE properties which depend on the CNT content in CNT/Al composites, all of them might be good alternatives depending on the application purpose. [ABSTRACT FROM AUTHOR]

Al composite foams reinforced by in-situ generated MgAl 2 O 4 spinel whiskers were fabricated via sintering and dissolution processes, using sodium chloride particles as a space holder material. The MgAl 2 O 4 spinel whiskers with diameters ranging from 50 to 300 nm were uniformly distributed in the composite foams and formed well-bonded interface with the Al matrix. The mean pore sizes and the average thickness of the cell wall are about 450 μm and 20 μm, respectively, while the relative density is 0.3. Compressive tests verified that the plateau stress is in the range of 5.4–18.7 MPa at the pore size of 0.45 mm, while the relative density increases from 0.2 to 0.5. Especially, the composite foams showed superior plateau stress (18.7 MPa) and energy absorption capacity (17.5 MJ/m 3 ) by adding 10 wt% Mg powder in starting materials. [ABSTRACT FROM AUTHOR]

In-situ synthesized carbon nanotubes (CNTs) reinforced aluminum–copper (Al–Cu) composites have been prepared by powder metallurgy. The strengthening effect of CNTs reinforcement and precipitation hardening of Al–Cu matrix has been investigated. CNTs and Cu nanoparticles are homogeneously embedded into Al powders through the process of in-situ preparation and ball milling. XRD results show that Cu elemental phase is converted to Al 2 Cu phase during the procedure of sintering. Raman spectra indicate that CNTs could maintain its structural integrity during powder metallurgy. In T6 heat treatment, the aging time of peak hardness has been reduced from 9 h to 3 h, demonstrating accelerated aging of the composite. Besides, the ultimate tensile strength of CNTs/Al–Cu composites have a 33.9% increase compared with that of Al–Cu alloy, and a further increase could be achieved (20.3%) after T6 heat treatment. The strengthening mechanism of CNTs/Al–Cu composites combines two synergistic factors: CNTs reinforcement and precipitation hardening of Al–Cu alloy. [ABSTRACT FROM AUTHOR]

In-situ generated MgAl 2 O 4 nanowhiskers, with diameters ranging from 30 to 200 nm, reinforced 6061 aluminum alloy composites have been successfully synthesized by reaction hot pressing under a relatively low temperature (600 °C). The effects of temperature and pressure on the morphology of MgAl 2 O 4 whiskers, as well as microstructure, densification and mechanical properties of the composites were investigated in detail. The results indicate that the MgAl 2 O 4 nanowhiskers with aspect ratio about 10–50 are uniformly distributed and firmly bonded with the matrix. Most of the nanowhiskers acting as bridges penetrate into the Al particles to form a framework bearing and transferring extrinsic loads. The high-resolution transmission electron microscope observation reveals that the MgAl 2 O 4 /Al interface is clean, smooth and free from interfacial product, and the whiskers have well-bonded interfaces with matrix. Additionally, the composites, prepared by sintering at 600 °C under the pressure of 50 MPa, exhibit the optimal performance. [ABSTRACT FROM AUTHOR]

• High temperature mechanical behavior of MgAlB 4 w/Al was studied. • UTS of 20 wt% MgAlB 4 w/Al composite at 300 °C can reach up to 166 MPa. • The failure behavior changes from the whisker fracture to interfacial debonding. High temperature tensile properties and fracture mechanism of the MgAlB 4 w/Al composites. [Display omitted] Aiming at developing high temperature resistance aluminum matrix composites for both structural and functional purposes, the novel MgAlB 4 whisker reinforced Al matrix composites with directional distributed reinforcement were fabricated using powder metallurgy followed by hot extrusion. The microstructure characterization demonstrated that Al grains exhibited a distinct< 111 > Al texture and MgAlB 4 whiskers aligned along the extrusion direction in the as-extruded composites. The high temperature tests indicate that UTS of the 20 wt% MgAlB 4w /Al composite at 200 °C and 300 °C can reach up to 266 MPa and 166 MPa, respectively, with a CTE of 23.7 × 10−6 K−1 at 300 °C. The whiskers distributed within the grains have a pinning effect on the dislocation movement and the whiskers distributed on the grain boundaries impede the grain boundaries sliding and migration. Additionally, the failure behavior changes from MgAlB 4 whiskers fracture to interfacial debonding of MgAlB 4w -Al matrix as the temperature increases. [ABSTRACT FROM AUTHOR]

Abstract: An approach was developed to fabricate carbon nanotube (CNT)-reinforced Al composites. In a typical process, the Co catalyst was evenly deposited on the surface of Al powder by impregnation route, and then the CNTs were grown in the Al powder by chemical vapor deposition to obtain CNT/Al powders. After ball-milling of the obtained powders for a short time, the CNT/Al composites were fabricated by compacting, sintering and hot extrusion of the ball-milled powders. During this process, the well dispersed CNT reinforcement is deeply embedded in the Al powder forming an effective interface bonding with matrix. As a result, the CNT/Al composites containing 2.5wt.% CNTs exhibit the ultimate tensile strength of 334MPa which is 1.7 times higher than that of unreinforced Al, and good ductility of ∼18% elongation to failure. Thus, well-balanced strength and ductility are achieved in CNT-reinforced Al composites. [Copyright &y& Elsevier]

Abstract: In this study, a novel MgAl2O4 spinel whisker reinforced composite was synthesized in situ in an Al matrix by a powder metallurgy technique. In MgAl2O4/Al composite, the whisker content was varied from 3% to 15% in weight and each one was completely investigated. The as-produced MgAl2O4/Al composites were hot extruded and MgAl2O4/Al composites rods with high relative density were obtained. Both the hardness and the softening temperature of the composites increased with increasing content of MgAl2O4 whisker. The dilatometric measurements show that MgAl2O4 whisker reinforced Al composites exhibit better thermal stability and lower thermal expansion coefficient than aluminum alloys. Moreover, wear resistance is also enhanced due to the formation of the whisker-formed network structure which is capable of bearing and transferring abrasion effect. Thus, the enhanced properties of the composites could be obtained. [Copyright &y& Elsevier]

Simultaneously achieving high strength and ductility is a critical issue for graphene reinforced aluminum matrix composites, which couldn't be resolved by the conventional mechanical milling-powder metallurgy technology due to the following reasons. On one hand, the low addition of graphene in the matrix traceable to its poor dispersibility limits the further strength improvement. On the other hand, the introduced graphene tends to distribute into grain boundaries rather than inside grains, which would result in stress concentrations at grain boundaries and localized strains, leading to the poor ductility of graphene/Al composites. In this work, intragranular nano-sized graphene nanoplates with high-content were dispersed in the matrix uniformly by a modified ball milling strategy, which induces that the strength and uniform elongation of the composites were simultaneously enhanced due to the improved work hardenability. Furthermore, the strengthening and toughening mechanisms were also discussed. This work offers a new insight into the fabrication and design of graphene/Al composites with both high strength and ductility. [ABSTRACT FROM AUTHOR]

For nanocarbon reinforced aluminum matrix composites (AMCs), the architecture design of reinforcements is an effective route to obtain superior mechanical performances. In this work, a novel AMC reinforced by CNTs wrapped with γ-Al 2 O 3 (CNTs@Al 2 O 3) reinforcement with balanced strength and toughness was fabricated by powder metallurgy methods. The wrapping structure of γ-Al 2 O 3 was synthesized through the in-situ reactions of Al matrix and boric acid decorated CNTs, thus improving the interface coupling of the composite. The CNTs@Al 2 O 3 /Al composite with the addition of 0.5 wt% CNTs and 10 wt% in-situ Al 2 O 3 exhibited a mean ultimate tensile strength of 404 MPa, which is significantly higher than unreinforced pure Al (183 MPa) and those reinforced by individual CNTs (207 MPa) or Al 2 O 3 (289 MPa). An improvement of ductility was also achieved in CNTs@Al 2 O 3 /Al composites compared with the Al 2 O 3 /Al composites with the same Al 2 O 3 content. The synergistic strengthening and toughening effects are ascribed to the ingenious in-situ CNTs@Al 2 O 3 wrapped structure, which highlights the importance of architecture design of reinforcements in AMCs, and sheds new light on the development of CNT-reinforced AMCs. Image 1 • A CNTs wrapped with in-situ γ-Al 2 O 3 reinforcement structure (CNTs@Al 2 O 3) was achieved. • Synergistic strengthening effect between CNTs and Al 2 O 3 was attributed to the unique wrapped structure. • The enhanced interfacial coupling improves load-transfer capability and hinders crack propagation. • The superior mechanical performance with balanced strength-toughness was obtained. [ABSTRACT FROM AUTHOR]