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Dissatisfactory load transfer has been a critical issue in carbon nanotube (CNT)- and graphene-reinforced metal matrix composites (MMCs) mainly because of the intrinsically unpleasant carbon-metal interfaces. Here we show by introducing in-situ Al 2 O 3 nanoparticles at aluminum (Al)-CNTs interface, the load transfer efficiency can be noticeably enhanced in powder metallurgy CNTs/Al composites. From in-situ tensile tests, the nanoparticle-modified Al-CNTs interfaces result in CNT fracture, a sign of high load transfer efficiency; while clean interfaces without nanoparticles lead to CNT pulling-out. The nanoparticle-induced enhancement of interface strength can be explained by the increased sliding resistance of CNTs in MMCs at the wake of cracks under tensile loading. Our study provides a new strategy for designing strong carbon-metal interfaces to fabricate high-performance nanocarbon-reinforced MMCs. Image 1 • A type of strong Al-CNT interface was studied by TEM and in-situ tensile tests. • Clean Al-CNT interfaces led to CNT pulling-out. • Al-CNT interfaces with in-situ alumina nanoparticles resulted in CNT fracture. • Alumina nanoparticles increased interfacial strength without damaging CNT structure. [ABSTRACT FROM AUTHOR]

In the present work, we studied the effect of the aspect ratio of carbon nanotubes (CNTs) on strengthening aluminum metal matrix composites (Al MMCs). To this end, Al samples reinforced with CNTs of various aspect ratios were produced via three different powder metallurgy methods. Microstructural examination revealed that the CNTs were uniformly dispersed in the materials with a range of aspect ratios from 6.5 to 55. The tensile results showed that the CNTs exhibited a strong strengthening effect in the composites regardless of their aspect ratios. However, the post-loading examination and quantitative analysis indicated that there was a strengthening mechanism transition for CNTs, which was closely associated with the aspect ratio or length of CNTs. The origin of such transition was explored from the viewpoint of dislocation-CNTs interaction under loading. The findings may provide a new insight in understanding the strengthening behaviors of CNT-reinforced MMCs. [ABSTRACT FROM AUTHOR]

Novel Cu-based composites with niobium selenide (NbSe2) and reduced graphene oxide (RGO) were sucessfully fabricated using powder metallurgy method (PM). The physical and tribological behaviors of composites were systematically studied. It was found that compared with copper, Cu-based composites showed increased hardness and decreased density. Besides, Cu-based composites with 18wt.% NbSe2 and 2wt.% RGO possessed the excellent tribological properties among all composites. According to experimental data analysis, a complete and dense tribo-film was formed on the worn surface, mainly composing of Fe2O3, CuO, Nb2O5, RGO and NbSe2 thiner sheets exfoliated. [ABSTRACT FROM AUTHOR]

The tribological properties of Cu-based composites with niobium diselenide (NbSe2) and titanium diboride (TiB2) were investigated systematically by a ball-on-disk multi-functional tribometer, scanning electron microscopy equipped with EDS and Laser Raman Spectrometer. Results showed that the friction-reducing and anti-wear properties of copper matrix composites were enhanced greatly, especially for the simultaneous addition of 10%wt.NbSe2 and 10%wt.TiB2, which was attributed to the synergetic effect of NbSe2 and TiB2. [ABSTRACT FROM AUTHOR]

Many studies have shown that carbon nanotubes (CNTs) have excellent strengthening effect as a reinforcement in pure aluminum (Al). However, it is unknown that whether such merit can be also achieved in strong Al alloys for achieving higher-strength Al matrix composites. In this study, CNTs were incorporated into pure Al and a high-strength Al alloy (AA5083) via the same powder metallurgy route. Results showed that during the dispersion stage, the high energy ball milling process caused different amounts of deformation to pure Al and AA5083, which led to a better dispersion state of CNTs in powders and composites of pure Al. Although the two composites had the same tensile strength coincidentally, the reinforcing effect of CNTs in pure Al composite was more than five folds larger than that in AA5083, suggesting a strong matrix effect on strengthening behavior of CNTs in Al matrix composites. The present finding may show significant guidance for the optimization of fabrication processes and development of high-performance CNTs/Al composites. [Display omitted] • Strengthening behavior of CNTs/pure Al and CNTs/AA5083 composites were compared. • The dispersion states of CNTs in the CNTs/pure Al and CNTs/AA5083 composites were compared especially. • The reinforcing efficiency of CNTs under poor dispersion state and fine dispersion state were discussed. [ABSTRACT FROM AUTHOR]

In this study, a pre-mixing process was applied to assist a high-energy ball milling (HEBM) process to fabricate high-strength aluminium (Al) matrix composites reinforced with carbon nanotubes (CNTs) by powder metallurgy. Effects of initial state on the dispersion quality of CNTs in composites and resultant mechanical properties were investigated using electron microscopy and tensile testing, respectively. Results showed that after pre-mixing, raw CNT agglomerations became flattened CNT clusters, and evolved into individually dispersed CNT fragments on flaky Al powder surface after HEBM for 12 h. However, CNT clusters remained in the same HEBM process without pre-mixing. Both individual CNTs and CNT clusters were observed inside cold-welded Al particles with a prolonged milling time of 24 h. By applying pre-mixing, the reinforcing effect in CNT/Al composites increased by more than 100%. The distinct evolution processes of CNT dispersion during HEBM with different initial states have been discussed. [ABSTRACT FROM PUBLISHER]

• Nano SiCp was used to decorate the FLG-Ti interface in FLG reinforced Ti matrix composite. • The structural integrity of FLG in the composite was protected by SiCp decoration. • The in-situ chemical reaction between FLG and Ti was inhibited by SiCp coating. • The thickness of the in-situ TiC layer on the interface decreased due to the SiCp decoration. • The functionality of SiCp decoration was clarified via thermodynamic and kinetic calculations. [Display omitted] The high reaction tendency between graphene and titanium (Ti) matrix during fabrication of graphene/Ti composites aggravates the structural integrity of graphene and limits its outstanding strengthening potential. In order to solve this problem, in this study, few-layered graphene (FLG) decorated with SiC nanoparticles (SiCp@FLG) was synthesized to reinforce Ti-6Al-4V (Ti64) alloy via a powder metallurgy route. Microstructure and Vickers hardness of the developed SiCp@FLG/Ti64 composites were studied systematically. Results showed that the SiCp decoration changed the morphology of FLG/Ti interface from continuous TiC reaction layer to discontinuous TiC nanoparticles during hot-press sintering. This discontinuous interface not only kept the integrity of FLG by suppressing its reaction with Ti matrix but also led to direct bonding between FLG and Ti. This designing strategy of protecting the reinforcement by secondary particle decoration can be potentially applied to the development of high-performance metal matrix composites. [ABSTRACT FROM AUTHOR]

Abstract: Casting aluminum alloys is a kind of materials containing numerous voids. Assuming these voids are cylindrical or spherical, a representative volume element of the material is isolated and investigated. Through the analysis of the velocity and strain fields of the cylindrical and spherical void-cell models and making use of a nonclassical elastoplastic constitutive relation, the microscopic stress fields of the two kinds of void-cell models are obtained, and it is further transformed to macroscopic stress using the principle of energy coincidence. Combining the evolution of void growth with that of void nucleation, the void evolution rule is obtained. The obtained expression of macroscopic stress and the void evolution rule are embedded in a simple mechanical model, an elastoplastic constitutive description is developed, which can take into account the effect of void evolution and large deformation. The corresponding numerical algorithm and finite element procedure are developed and applied to the analysis of the elastoplastic response and the porosity of casting aluminum alloy A104. The computed results show satisfactory agreement with experiments. [Copyright &y& Elsevier]

In order to study the effect of carbon ion implantation on the aqueous corrosion behavior of ZIRLO alloy, specimens were implanted with carbon ions with fluence ranging from 1 × 1016 to 1 × 1017 ions/cm², using a metal vapor vacuum arc source (MEVVA) at an extraction voltage of 40 kV. The valence states and depth distributions of elements in the surface layer of the samples were analyzed by X-ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES), respectively. Transmission electron microscopy (TEM) was used to examine the microstructure of the carbon-implanted samples. Glancing angle X-ray diffraction (GAXRD) was employed to examine the phase transformation due to the carbon ion implantation. The potentiodynamic polarization technique was employed to evaluate the aqueous corrosion resistance of implanted ZIRLO alloy in a 1 M H2SO4 solution. It was found that a significant improvement was achieved in the aqueous corrosion resistance of ZIRLO alloy implanted with carbon ions. The higher the fluence, the worse is the corrosion resistance. Finally, the mechanism of the corrosion behavior of carbon-implanted ZIRLO alloy was discussed. [ABSTRACT FROM AUTHOR]

The compound Ti3SiC2 is a promising reinforcement for copper, but at a high volume content of Ti3SiC2, densification of Cu/Ti3SiC2 composites becomes difficult. To improve the densification behaviour and microstructure of Cu/Ti3SiC2 composites, Ti3SiC2 particulates were coated with a layer of copper by an electroless plating method before being incorporated into the copper matrix. Results demonstrated that, compared with uncoated Ti3SiC2 reinforced copper, copper coated Ti3SiC2 reinforced composites exhibit both high density and a homogeneous distribution of Ti3SiC2 within the copper matrix. The precoated layer of copper prevents direct contact and agglomeration of Ti3SiC2 particulates. Owing to the improved density and microstructure, the mechanical properties of Cu/Ti3SiC2 composites are also enhanced. Mechanical property investigation revealed that a significant strengthening effect is observed for Cu/Ti3SiC2 composites at both room and high temperatures. [ABSTRACT FROM AUTHOR]

In this study, the origin of the high tensile ductility (>10% strain to fracture) of a new class of high-strength (yield strength >500 MPa) aluminium (Al) metal matrix composites (Al MMCs) co-reinforced by ex-situ carbon nanotubes (CNTs) and in-situ γ−Al 2 O 3 nanoparticles was investigated. The microstructures of these unique Al MMCs prior to and post tensile testing were characterized in detail using high resolution transmission electron microscopy, in order to understand their response to tensile deformation. The pathways to the in-situ formation of γ−Al 2 O 3 nanoparticles were identified and attributed to the high energy ball milling process, and the subsequent spark plasma sintering, which converted the amorphous Al-oxide into γ−Al 2 O 3 nanoparticles. The in-situ γ−Al 2 O 3 nanoparticles and Al matrix exhibited a semi-coherent interface, which led to a markedly increased dislocation density in the matrix around the nanoparticles during tensile deformation. These dislocations were precursors to microvoid formation and consequent dimples on further deformation. The co-operation of CNTs and γ−Al 2 O 3 nanoparticles resulted in a long strain-softening stage and therefore excellent tensile ductility. The results suggested that the exploitation of hybrid reinforcement by ex-situ CNTs and in-situ nanoparticles can enable the fabrication of high-performance metal matrix composites. [ABSTRACT FROM AUTHOR]

In this study, for the first time few-walled carbon nanotubes (FWCNTs) with ∼3 walls were used as reinforcements in fabricating high performance aluminum matrix composites (AMCs). FWCNTs/Al composites and referential Al materials were prepared by a powder metallurgy route consisting of high energy ball milling, spark plasma sintering (SPS) and subsequent hot extrusion. It is found that, by decreasing SPS temperature and time, FWCNTs/Al composites showed reduced grains with an increased dislocation density and improved structural integrity of FWCNTs, leading to an increased tensile strength. Meanwhile, comparatively high strain hardening rates and long strain softening behavior were observed after necking in the sample sintered at 500 °C, which resulted in a tensile elongation of 11.7% with a high yield strength of 382 MPa. The experimental results suggested that, compared with traditional multi-walled carbon nano-tubes (MWCNTs), FWCNTs showed a noticeably enhanced strengthening effect and provided a good balance of strength and ductility in Al composites. It may make FWCNTs a good reinforcement candidate for metal matrix composites to achieve improved mechanical properties. • For the first time FWCNTs were used as reinforcements in Al matrix composites. • FWCNTs/Al have long strain softening stage after necking. • FWCNTs/Al sintered at 500 °C has yield strength of 382 MPa and tensile elongation of 11.7%. • FWCNTs have better strengthening effect than MWCNTs. [ABSTRACT FROM AUTHOR]

• For the first time in-situ high-temperature TEM is performed on a CNT/Al composite. • At elevated temperatures dislocation bands are observed to move. • Dislocations are pinned by CNTs to form low angle grain boundaries (LAGBs). • Abundant dislocations and long CNTs contribute to formation of high fraction LAGBs. In this study, in-situ high-temperature transmission electronic microscopy is performed to investigate the formation mechanism of high-fraction (>50%) low-angle grain boundaries (LAGBs) in carbon nanotubes/aluminum (CNTs/Al) composites with balanced strength and ductility. During heating up the low-temperature-sintered composite, we find that dislocation bands first moves and then they are pinned by CNTs to form LAGBs. Abundant dislocations in the Al matrix and large-aspect-ratio CNTs are clarified as two critical factors for producing LAGBs. This study provides new insight into the effect of CNTs on the microstructural and mechanical properties of metal matrix composites. [ABSTRACT FROM AUTHOR]

Existing aluminium metal matrix composites (Al MMCs) can attain both high tensile yield strength (>500 MPa) and high elastic modulus (>90 GPa) but usually at the expense of tensile strain-to-fracture (~5% or less). Here we report the development of a novel class of Al MMCs that can offer tensile yield strength of 515 ± 17 MPa, elastic modulus of 95.6 ± 1.7 GPa and tensile strain-to-fracture of 10.4 ± 0.8%. Our design hypothesis is to reinforce the Al matrix with ex situ introduced carbon nanotubes (CNTs) for primary strengthening but at the same time we craft a high number density of in situ formed ultrafine γ-Al 2 O 3 nanoparticles to improve dimple fracture. Together they act in concert to render outstanding tensile properties. The strengthening and failure mechanisms of the as-fabricated Al-CNTs-γ-Al 2 O 3 MMCs are characterized in detail. The design concept proposed and validated in this study can be informative for the fabrication of other high-performance carbon-reinforced MMCs. [ABSTRACT FROM AUTHOR]

To keep high structural integrity of carbon nanotubes (CNTs) in titanium (Ti), sintering and sintering-based consolidation processes were widely applied to fabricate CNTs/Ti composites. However, sintering processes were faced with the dilemma between insufficient densification at low sintering temperatures and excessive CNTs-Ti reaction at high temperatures. In this study, a sintering-free process combining cold compaction and hot extrusion (CC-HE) was developed to fabricate CNTs/Ti composites. The CC-HE-processed CNTs/Ti composites achieved superior tensile strength of 1262 MPa, which registered the new record among the pure Ti matrix composites reinforced with CNTs and graphene in available literature. By comparison study on CC-HE and the referential sintered CNTs/Ti composites, it was revealed that the high strength of CC-HE composites was attributed to the improved effects of grain refinement and secondary-phase strengthening, as a result of enhanced CNT integrity. The results provide a facile and large-scale-production pathway to fabricate high-performance carbon/Ti composites, which can be also applicable to other metal matrix composites. [Display omitted] • Developed novel fabrication method combining cold compaction and hot extrusion. • Fabricated CNTs/Ti composite achieved ultimate tensile strength of 1262 MPa. • Cold compaction helps to reserve CNTs integrity and restrain in-situ reaction. • Cold compaction brings larger lattice distortion and finer grain size to matrix. • Cold compaction increases the secondary phase strengthening effect. [ABSTRACT FROM AUTHOR]

In order to study the effect of carbon ion implantation on the aqueous corrosion behavior of ZIRLO alloy, specimens were implanted with carbon ions with fluence ranging from 1 × 1016 to 1 × 1017 ions/cm², using a metal vapor vacuum arc source (MEVVA) at an extraction voltage of 40 kV. The valence states and depth distributions of elements in the surface layer of the samples were analyzed by X-ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES), respectively. Transmission electron microscopy (TEM) was used to examine the microstructure of the carbon-implanted samples. Glancing angle X-ray diffraction (GAXRD) was employed to examine the phase transformation due to the carbon ion implantation. The potentiodynamic polarization technique was employed to evaluate the aqueous corrosion resistance of implanted ZIRLO alloy in a 1 M H2SO4 solution. It was found that a significant improvement was achieved in the aqueous corrosion resistance of ZIRLO alloy implanted with carbon ions. The higher the fluence, the worse is the corrosion resistance. Finally, the mechanism of the corrosion behavior of carbon-implanted ZIRLO alloy was discussed. [ABSTRACT FROM AUTHOR]

Aluminum composites reinforced with carbon-based nano-particles or fibers have been widely studied. Yet, the rate dependence of their properties has been barely reported. In the present study, CNTs-reinforced Al composites with CNTs of two aspect ratios were produced by different powder metallurgy methods, followed by spark plasma sintering and hot extrusion. The mechanical properties and the underlying mechanisms of CNTs-reinforced Al composites at various loading rates were studied, with the aim of exploring the role of CNTs on strengthening, esp. on rate-dependent properties. The mechanical experiments revealed that the addition of CNTs not only increased the strength but also the strain rate sensitivity in comparison with pure Al. It was found that, under dynamic loading, the materials showed an increased strength and elongation-to-failure simultaneously, due to improved strain hardening rates. A careful analysis suggested that the long-range back stress produced at the CNTs-Al interfaces and the geometrically necessary dislocations accumulated due to strain gradient along the interface, mainly contributed to the strain hardening of CNTs/Al composites. A novel microstructure-based model using microscopically non-uniform dispersion of CNTs was proposed to account for the mechanical properties with better prediction than the traditional models. The results might shed some light on understanding metal matrix composites reinforced with nano-particles or fibers. [ABSTRACT FROM AUTHOR]

Homogeneous graphene dispersion and suitable interface bonding are two key challenges to realize the high strengthening potential of graphene in metal matrix composites (MMCs). In this study, graphene nanosheets (GNSs) with deposited nickel (Ni) nanoparticles were synthesized to simultaneously overcome the two challenges. Ni-coated-GNS-reinforced aluminum (Al) MMCs were fabricated by graphene synthesis, Ni decoration and subsequent powder metallurgy. It was revealed that Ni-coated GNSs exhibited noticeably enhanced strengthening effect compared with graphene reinforcements in most previous studies. With the addition of 1.5 wt% Ni-coated GNSs, the composites exhibited 132% higher strength than that of unreinforced aluminum. The enhancement in Vickers hardness and Young's modulus further confirmed the remarkable strengthening effect. The high strength and high Young's modulus were examined by strengthening models, and a comparison between experimental and theoretical values was reached. The main strengthening mechanisms in the Ni-coated GNSs/Al composites were clarified as dislocation-related ones. [ABSTRACT FROM AUTHOR]

Powder metallurgy magnesium (Mg) composites reinforced with multi-walled carbon nanotubes (MWCNTs) were developed by an effective three-step process. CNTs were uniformly dispersed on the Mg powders surface without damaged structure. A large amount of twins appeared in the as-extruded CNT/Mg composites, and the basal texture was weakened comparing to as-extruded pure Mg, which played a positive role in the ambient tensile deformation. The elongation to failure of Mg composite with 0.08 wt% CNTs has increased greatly by 32%. [ABSTRACT FROM AUTHOR]