The research works of graphene-reinforced metal matrix composites will be summarised in this pape... more The research works of graphene-reinforced metal matrix composites will be summarised in this paper. Comparatively, much less research works have been undertaken in this field. Graphene has been thought to be an ideal reinforcement material for composites due to its unique two-dimensional structure and outstanding physical and mechanical properties. It is expected to yield structural materials with high specific strength or functional materials with exciting thermal and electrical characteristics. This paper will introduce all kinds of graphene-reinforced metal matrix composites that have been studied. The microstructure and mechanical properties, processing techniques, graphene dispersion, strengthening mechanisms, interfacial reactions between graphene and the metal matrix and future research works in this field will be discussed.
objects with higher indentation resistance, such as body armors, shock absorbers, and packing mat... more objects with higher indentation resistance, such as body armors, shock absorbers, and packing materials. Since the pioneering work of Lakes on the negative Poisson's ratio of foam structures in 1987, many natural objects or designed artifi cial systems such as bucklicrystals, tailored 2D graphene, CNT sheets, 2D/3D metallic lattices, ceramic sponges, cork stoppers, and dip-in direct-laserwriting 3D nanostructures have demonstrated negative Poisson's ratios effects. Moreover, metamaterials with re-entrant structures exhibit higher negative Poisson's ratio and much larger indentation resistance under longitudinal compression than those of conventional porous scaffolds because these anomalous properties primarily depend on topological microstructures rather than material compositions. Some reported graphene monoliths have exhibited large compressibility and high loading-to-weight ratios (≈40 000) as soft materials but poor tensile resistance due to intrinsic brittleness and weak antisliding stability of interface between graphene sheets. Such graphene monoliths often present early fracture, low stiffness, and poor fatigue resistance as long as suffering a large tensile strain, which have greatly limited their applicability in engineering. However, a negative Poisson's ratio response causes transverse contraction during longitudinal compression, leading to triaxial compression states and larger volume shrinkage, and even compressive strain in the whole bulks. Such metamaterials can exhibit superior mechanical properties (e.g., energy absorbing capacity, indentation/fracture resistance, ultimate strength, maximum elastic strain, and fatigue life). To further benefi t mechanical robustness and to overcome the challenge of poor tensile resistance of graphene monoliths, signifi cant attention is warranted to develop a scalable graphene metamaterial (GM) with a reentrant microstructure and negative Poisson's ratio response. In this article, we highlight the synthesis of GM with wellordered hyperbolic pattern and hierarchical honeycomb-like scaffold of microstructure by a modifi ed hydrothermal approach and subsequent oriented freeze-casting process. The designed local oriented 'buckling' responses of multilayer graphene cellular walls in the microstructure generate a tremendously large macroscopic negative Poisson's ratio ( ν = −0.38) that is tunable by adjusting the structural porosity ( λ ) or effective bulk density ( ρ e ) of the GM (where ρ e defi nes as ρ e = ρ 0 /(1−| ε 11 |) during compression, ρ 0 is the density of GM at free state). The impacts of freeze-casting orientation and macroscopic aspect ratio (height, L, to diameter, D : L/D ) on the Poisson's ratio are systematically elucidated. Moreover, the mechanisms of negative Poisson's ratio and compressive strain mapping of GM are investigated by in situ observations of microstructural evolution 3D macroscopic graphene monoliths such as microlattices, hydrogels, sponges, petal arrays, and aerogels offer a promising combination of lightweight (<10 mg cm −3 ), large specifi c surface area (≈200 m 2 g −1 ), outstanding electrical conductivity (≈20 S cm −1 ) and excellent thermal insulating capacity (≈15 mW m −1 K −1 ). Such 3D graphene functional materials have demonstrated their widespread applications in scientifi c and engineering fi elds, including stretchable electronics, energy storages, magnetic actuated elastomers, and electrochemical catalysis. Most contemporary reports focus on mechanical compressibility, electric conductivity, and electrochemical performance, but few on Poisson's ratio,
To realize this goal, we developed a novel 3D printing technique, as illustrated in , by integrat... more To realize this goal, we developed a novel 3D printing technique, as illustrated in , by integrating 3D printing ice and freeze casting to print GA. Different from other 3D printing processes where the materials are heated up or extruded out at room temperature, our 3D printing technique, illustrated in a, rapidly freezes the water based GO suspension and selectively solidifi es the aqueous droplets into ice crystal on a cold sink (−25 °C), well below water's freezing point. Therefore, the water, shown in b, and low viscous Newtonian GO suspension, shown in c, can be printed by drop-on-demand mode, where the material is ejected drop by drop only if needed. The dilute pure aqueous GO suspension, with low GO density (1 mg mL −1 ), offers lower density and larger surface area for printed GA when compared with the-state-of-the-art printing technique for GA. In traditional continuous deposition based 3D printing, physical properties of printed parts are negatively infl uenced by insuffi cient bonding at the interface driven by intermolecular diffusion and the undesirable voids between the adjacent fi laments. In our printing process, when liquid solution is deposited on top of previously frozen material, the not-yet-frozen material melts the already frozen surface. These two materials are mixed and refrozen together under low temperature (−25 °C). Because the remelted aqueous material possesses low viscosity, the voids between layers are instantly fi lled by the liquid material under surface tension and gravity. Since the deposited materials freeze and fi rmly bond together with the previous layer via hydrogen bond, high structural integrity of the fi nal assembled GA can be achieved, as further confi rmed in the mechanical test section. The pure water serves as a supporting structure to build complex architecture with overhang features. As shown in , the post processing includes immersion of 3D printed architectures in liquid nitrogen, freeze drying to remove the water, and thermal annealing to achieve a 3D printed ultralight GA truss. As shown in g, 2.5 D (left) and truly 3D truss (right), GO aerogel structure can be printed. We also printed grid GO aerogel structures with various wall thicknesses, decreasing from left to right in h, in order to demonstrate the printing ability. -c (Supporting Information) illustrates more 3D printed GO aerogels on catkin and -f (Supporting Information) shows various design and structures with different wall thicknesses. Compared to the continuous printing mode, the drop-on-demand technique achieves higher precision and is easier to extend for printing multiple materials with multinozzles, paving the way for fabrication of multifunctional aerogel materials in myriad applications.
A new method to generate large scale and highly dense nanoholes is presented in this paper. By th... more A new method to generate large scale and highly dense nanoholes is presented in this paper. By the pulsed laser irradiation under water, the hydrogen etching is introduced to form high density nanoholes on the surfaces of AISI 4140 steel and Ti. In order to achieve higher nanohole density, laser shock peening (LSP) followed by recrystallization is used for grain refinement. It is found that the nanohole density does not increase until recrystallization of the substructures after laser shock peening. The mechanism of nanohole generation is studied in detail. This method can be also applied to generate nanoholes on other materials with hydrogen etching effect.
This study investigates the fundamental mechanism of fatigue performance enhancement during a nov... more This study investigates the fundamental mechanism of fatigue performance enhancement during a novel hybrid manufacturing process, which combines laser sintering of superhard nanoparticles integrated nanocomposites and laser shock peening (LSP). Through laser sintering, TiN nanoparticles are integrated uniformly into iron matrix to form a nanocomposite layer near the surface of AISI4140 steel. LSP is then performed on the nanocomposite layer to generate interaction between nanoparticles and shock waves. The fundamental mechanism of fatigue performance enhancement is discussed in this paper. During laser shock interaction with the nanocomposites, the existence of nanoparticles increases the dislocation density and also helps to pin the dislocation movement. As a result, both dislocation density and residual stress are stabilized, which is beneficial for fatigue performance.
A general approach to generate dense nanostructure on various substrates has been investigated in... more A general approach to generate dense nanostructure on various substrates has been investigated in this paper. During this process, so called pulsed laser induced confined vapor deposition (PLCVD), a pulsed laser irradiation with a transparent confinement was applied to various surfaces, such as gold thin film on silicon wafer, AA6061 alloy and silicon wafer. When a 20 nm thick Au film was irradiated by 3 kHz pulsed laser, a short-range ordered thin layer of nanoparticles with average diameter of 9.0 ± 3.5 nm and density of 43.8 × 1010 cm−2 is observed. Highly dense alumina nanoparticles were deposited on surface of AA6061 alloy by PLCVD process. Several silicon nanostructures, such as nanoparticles and microrings, can be produced under different experimental conditions. The formation mechanisms of these nanostructures were also discussed.
Uniform distribution of carbon nanotubes (CNTs) in metal matrix during additive manufacturing of ... more Uniform distribution of carbon nanotubes (CNTs) in metal matrix during additive manufacturing of nanocomposites is always a challenge since the CNTs tend to aggregate in the molten pool. In this study, Multiwall carbon nanotubes (MWNTs) were separated and distributed uniformly into iron matrix by laser sintering process. MWNTs and iron powders were mixed together by magnetic stir, coated on steel 4140 surface, followed by laser sintering. Due to the fast heating and cooling rate, the CNTs are evenly distributed in the metal matrix. The temperature field was calculated by multiphysics simulation considering size effects, including size dependent melting temperature, thermal conductivity, and heat capacity. The SEM, TEM, and XRD were used to understand the laser sintering of CNT integrated nanocomposites. The results proved the feasibility of this technique to synthesize MWNTS integrated metal matrix nanocomposites.
Highly dense 2D nanostructures are desirable in photocatalysis, water treatment and energy storag... more Highly dense 2D nanostructures are desirable in photocatalysis, water treatment and energy storage, due to their high surface to volume areas. This paper describes a novel approach combining thermal stress and magnetic force to generate highly dense α-Fe2O3 nanosheets on the surface of various iron substrates, including plates and powders. This technique involves the thermal oxidation of iron substrates on a hot plate with a magnetic field. The Lorentz force acting on the ions induced by the magnetic field facilitates the lateral growth of nanosheets. This effect results in a highly porous nanostructure consisting of dense 2D nanosheets with extremely large BET surface areas. The application of these nanosheets is explored in water treatment. Electron microscopic studies indicate that these nanosheets show a parabolic relation with time of thermal oxidation for the growth in the width direction. A comparison of heavy metal (As, Cr) ion adsorption of nanosheets and nanowires was also performed, which shows that nanosheets have a much better adsorption rate than nanowires.
Current three-dimensional (3D) printing techniques enable the fabrication of complex multifunctio... more Current three-dimensional (3D) printing techniques enable the fabrication of complex multifunctional structures that are unimaginable in conventional manufacturing. In this Perspective, we outline recent progress in materials and manufacturing and propose challenges and opportunities for the future development of 3D printing of functional materials. The success of future 3D printing relies not only on multifunctional materials and printing techniques but also on smart design of complex systems. Engineers need to understand advanced materials, additive manufacturing, and, more importantly, creative design. Fortunately, we can learn from many structures that exist in nature and adapt them to engineered structures.
This study investigates the integration of single-layer graphene oxide (GO) powders with iron mat... more This study investigates the integration of single-layer graphene oxide (GO) powders with iron matrix by laser sintering and its effects on mechanical strength and fatigue life. A laser-based additive manufacturing process is used to sinter GO and iron powders, and form GO–Fe nanocomposite materials. The aggregation of GO powders was prevented by the fast laser heating and cooling process. In addition, the evaporation of polyvinyl alcohol, which acted as a dispersing agent, from the cross-section helps align the GOs vertically in the cross-section. An energy-dispersive X-ray spectroscopy map from cross-sectional scanning electron microscopy images and Raman patterns together demonstrate the reduction of GOs after laser sintering. The GO–matrix interfacial structure was investigated by transmission electron microscopy. GOs were found to be stretched due to the rapid heating and cooling process during laser irradiation. Strengthening mechanisms of tensile strength and Young’s modulus were developed based on the laser sintering results. Surface microhardness was increased by 93.5% by laser sintering of 2 wt.% GO. The improvement in the fatigue life after laser sintering of GO-reinforced iron matrix nanocomposites was also investigated.
This paper reports a methodology of half-embedding nanoparticles into metallic materials. Transpa... more This paper reports a methodology of half-embedding nanoparticles into metallic materials. Transparent and opaque nanoparticles are chosen to demonstrate the process of laser assisted nanoparticle embedding. Dip coating method is used to coat transparent or opaque nanoparticle on the surface of metallic material. Nanoparticles are embedded into substrate by laser irradiation. In this study, the mechanism and process of nanoparticle embedding are investigated. It is found both transparent and opaque nanoparticles embedding are with high densities and good uniformities.
The research works of graphene-reinforced metal matrix composites will be summarised in this pape... more The research works of graphene-reinforced metal matrix composites will be summarised in this paper. Comparatively, much less research works have been undertaken in this field. Graphene has been thought to be an ideal reinforcement material for composites due to its unique two-dimensional structure and outstanding physical and mechanical properties. It is expected to yield structural materials with high specific strength or functional materials with exciting thermal and electrical characteristics. This paper will introduce all kinds of graphene-reinforced metal matrix composites that have been studied. The microstructure and mechanical properties, processing techniques, graphene dispersion, strengthening mechanisms, interfacial reactions between graphene and the metal matrix and future research works in this field will be discussed.
objects with higher indentation resistance, such as body armors, shock absorbers, and packing mat... more objects with higher indentation resistance, such as body armors, shock absorbers, and packing materials. Since the pioneering work of Lakes on the negative Poisson's ratio of foam structures in 1987, many natural objects or designed artifi cial systems such as bucklicrystals, tailored 2D graphene, CNT sheets, 2D/3D metallic lattices, ceramic sponges, cork stoppers, and dip-in direct-laserwriting 3D nanostructures have demonstrated negative Poisson's ratios effects. Moreover, metamaterials with re-entrant structures exhibit higher negative Poisson's ratio and much larger indentation resistance under longitudinal compression than those of conventional porous scaffolds because these anomalous properties primarily depend on topological microstructures rather than material compositions. Some reported graphene monoliths have exhibited large compressibility and high loading-to-weight ratios (≈40 000) as soft materials but poor tensile resistance due to intrinsic brittleness and weak antisliding stability of interface between graphene sheets. Such graphene monoliths often present early fracture, low stiffness, and poor fatigue resistance as long as suffering a large tensile strain, which have greatly limited their applicability in engineering. However, a negative Poisson's ratio response causes transverse contraction during longitudinal compression, leading to triaxial compression states and larger volume shrinkage, and even compressive strain in the whole bulks. Such metamaterials can exhibit superior mechanical properties (e.g., energy absorbing capacity, indentation/fracture resistance, ultimate strength, maximum elastic strain, and fatigue life). To further benefi t mechanical robustness and to overcome the challenge of poor tensile resistance of graphene monoliths, signifi cant attention is warranted to develop a scalable graphene metamaterial (GM) with a reentrant microstructure and negative Poisson's ratio response. In this article, we highlight the synthesis of GM with wellordered hyperbolic pattern and hierarchical honeycomb-like scaffold of microstructure by a modifi ed hydrothermal approach and subsequent oriented freeze-casting process. The designed local oriented 'buckling' responses of multilayer graphene cellular walls in the microstructure generate a tremendously large macroscopic negative Poisson's ratio ( ν = −0.38) that is tunable by adjusting the structural porosity ( λ ) or effective bulk density ( ρ e ) of the GM (where ρ e defi nes as ρ e = ρ 0 /(1−| ε 11 |) during compression, ρ 0 is the density of GM at free state). The impacts of freeze-casting orientation and macroscopic aspect ratio (height, L, to diameter, D : L/D ) on the Poisson's ratio are systematically elucidated. Moreover, the mechanisms of negative Poisson's ratio and compressive strain mapping of GM are investigated by in situ observations of microstructural evolution 3D macroscopic graphene monoliths such as microlattices, hydrogels, sponges, petal arrays, and aerogels offer a promising combination of lightweight (<10 mg cm −3 ), large specifi c surface area (≈200 m 2 g −1 ), outstanding electrical conductivity (≈20 S cm −1 ) and excellent thermal insulating capacity (≈15 mW m −1 K −1 ). Such 3D graphene functional materials have demonstrated their widespread applications in scientifi c and engineering fi elds, including stretchable electronics, energy storages, magnetic actuated elastomers, and electrochemical catalysis. Most contemporary reports focus on mechanical compressibility, electric conductivity, and electrochemical performance, but few on Poisson's ratio,
To realize this goal, we developed a novel 3D printing technique, as illustrated in , by integrat... more To realize this goal, we developed a novel 3D printing technique, as illustrated in , by integrating 3D printing ice and freeze casting to print GA. Different from other 3D printing processes where the materials are heated up or extruded out at room temperature, our 3D printing technique, illustrated in a, rapidly freezes the water based GO suspension and selectively solidifi es the aqueous droplets into ice crystal on a cold sink (−25 °C), well below water's freezing point. Therefore, the water, shown in b, and low viscous Newtonian GO suspension, shown in c, can be printed by drop-on-demand mode, where the material is ejected drop by drop only if needed. The dilute pure aqueous GO suspension, with low GO density (1 mg mL −1 ), offers lower density and larger surface area for printed GA when compared with the-state-of-the-art printing technique for GA. In traditional continuous deposition based 3D printing, physical properties of printed parts are negatively infl uenced by insuffi cient bonding at the interface driven by intermolecular diffusion and the undesirable voids between the adjacent fi laments. In our printing process, when liquid solution is deposited on top of previously frozen material, the not-yet-frozen material melts the already frozen surface. These two materials are mixed and refrozen together under low temperature (−25 °C). Because the remelted aqueous material possesses low viscosity, the voids between layers are instantly fi lled by the liquid material under surface tension and gravity. Since the deposited materials freeze and fi rmly bond together with the previous layer via hydrogen bond, high structural integrity of the fi nal assembled GA can be achieved, as further confi rmed in the mechanical test section. The pure water serves as a supporting structure to build complex architecture with overhang features. As shown in , the post processing includes immersion of 3D printed architectures in liquid nitrogen, freeze drying to remove the water, and thermal annealing to achieve a 3D printed ultralight GA truss. As shown in g, 2.5 D (left) and truly 3D truss (right), GO aerogel structure can be printed. We also printed grid GO aerogel structures with various wall thicknesses, decreasing from left to right in h, in order to demonstrate the printing ability. -c (Supporting Information) illustrates more 3D printed GO aerogels on catkin and -f (Supporting Information) shows various design and structures with different wall thicknesses. Compared to the continuous printing mode, the drop-on-demand technique achieves higher precision and is easier to extend for printing multiple materials with multinozzles, paving the way for fabrication of multifunctional aerogel materials in myriad applications.
A new method to generate large scale and highly dense nanoholes is presented in this paper. By th... more A new method to generate large scale and highly dense nanoholes is presented in this paper. By the pulsed laser irradiation under water, the hydrogen etching is introduced to form high density nanoholes on the surfaces of AISI 4140 steel and Ti. In order to achieve higher nanohole density, laser shock peening (LSP) followed by recrystallization is used for grain refinement. It is found that the nanohole density does not increase until recrystallization of the substructures after laser shock peening. The mechanism of nanohole generation is studied in detail. This method can be also applied to generate nanoholes on other materials with hydrogen etching effect.
This study investigates the fundamental mechanism of fatigue performance enhancement during a nov... more This study investigates the fundamental mechanism of fatigue performance enhancement during a novel hybrid manufacturing process, which combines laser sintering of superhard nanoparticles integrated nanocomposites and laser shock peening (LSP). Through laser sintering, TiN nanoparticles are integrated uniformly into iron matrix to form a nanocomposite layer near the surface of AISI4140 steel. LSP is then performed on the nanocomposite layer to generate interaction between nanoparticles and shock waves. The fundamental mechanism of fatigue performance enhancement is discussed in this paper. During laser shock interaction with the nanocomposites, the existence of nanoparticles increases the dislocation density and also helps to pin the dislocation movement. As a result, both dislocation density and residual stress are stabilized, which is beneficial for fatigue performance.
A general approach to generate dense nanostructure on various substrates has been investigated in... more A general approach to generate dense nanostructure on various substrates has been investigated in this paper. During this process, so called pulsed laser induced confined vapor deposition (PLCVD), a pulsed laser irradiation with a transparent confinement was applied to various surfaces, such as gold thin film on silicon wafer, AA6061 alloy and silicon wafer. When a 20 nm thick Au film was irradiated by 3 kHz pulsed laser, a short-range ordered thin layer of nanoparticles with average diameter of 9.0 ± 3.5 nm and density of 43.8 × 1010 cm−2 is observed. Highly dense alumina nanoparticles were deposited on surface of AA6061 alloy by PLCVD process. Several silicon nanostructures, such as nanoparticles and microrings, can be produced under different experimental conditions. The formation mechanisms of these nanostructures were also discussed.
Uniform distribution of carbon nanotubes (CNTs) in metal matrix during additive manufacturing of ... more Uniform distribution of carbon nanotubes (CNTs) in metal matrix during additive manufacturing of nanocomposites is always a challenge since the CNTs tend to aggregate in the molten pool. In this study, Multiwall carbon nanotubes (MWNTs) were separated and distributed uniformly into iron matrix by laser sintering process. MWNTs and iron powders were mixed together by magnetic stir, coated on steel 4140 surface, followed by laser sintering. Due to the fast heating and cooling rate, the CNTs are evenly distributed in the metal matrix. The temperature field was calculated by multiphysics simulation considering size effects, including size dependent melting temperature, thermal conductivity, and heat capacity. The SEM, TEM, and XRD were used to understand the laser sintering of CNT integrated nanocomposites. The results proved the feasibility of this technique to synthesize MWNTS integrated metal matrix nanocomposites.
Highly dense 2D nanostructures are desirable in photocatalysis, water treatment and energy storag... more Highly dense 2D nanostructures are desirable in photocatalysis, water treatment and energy storage, due to their high surface to volume areas. This paper describes a novel approach combining thermal stress and magnetic force to generate highly dense α-Fe2O3 nanosheets on the surface of various iron substrates, including plates and powders. This technique involves the thermal oxidation of iron substrates on a hot plate with a magnetic field. The Lorentz force acting on the ions induced by the magnetic field facilitates the lateral growth of nanosheets. This effect results in a highly porous nanostructure consisting of dense 2D nanosheets with extremely large BET surface areas. The application of these nanosheets is explored in water treatment. Electron microscopic studies indicate that these nanosheets show a parabolic relation with time of thermal oxidation for the growth in the width direction. A comparison of heavy metal (As, Cr) ion adsorption of nanosheets and nanowires was also performed, which shows that nanosheets have a much better adsorption rate than nanowires.
Current three-dimensional (3D) printing techniques enable the fabrication of complex multifunctio... more Current three-dimensional (3D) printing techniques enable the fabrication of complex multifunctional structures that are unimaginable in conventional manufacturing. In this Perspective, we outline recent progress in materials and manufacturing and propose challenges and opportunities for the future development of 3D printing of functional materials. The success of future 3D printing relies not only on multifunctional materials and printing techniques but also on smart design of complex systems. Engineers need to understand advanced materials, additive manufacturing, and, more importantly, creative design. Fortunately, we can learn from many structures that exist in nature and adapt them to engineered structures.
This study investigates the integration of single-layer graphene oxide (GO) powders with iron mat... more This study investigates the integration of single-layer graphene oxide (GO) powders with iron matrix by laser sintering and its effects on mechanical strength and fatigue life. A laser-based additive manufacturing process is used to sinter GO and iron powders, and form GO–Fe nanocomposite materials. The aggregation of GO powders was prevented by the fast laser heating and cooling process. In addition, the evaporation of polyvinyl alcohol, which acted as a dispersing agent, from the cross-section helps align the GOs vertically in the cross-section. An energy-dispersive X-ray spectroscopy map from cross-sectional scanning electron microscopy images and Raman patterns together demonstrate the reduction of GOs after laser sintering. The GO–matrix interfacial structure was investigated by transmission electron microscopy. GOs were found to be stretched due to the rapid heating and cooling process during laser irradiation. Strengthening mechanisms of tensile strength and Young’s modulus were developed based on the laser sintering results. Surface microhardness was increased by 93.5% by laser sintering of 2 wt.% GO. The improvement in the fatigue life after laser sintering of GO-reinforced iron matrix nanocomposites was also investigated.
This paper reports a methodology of half-embedding nanoparticles into metallic materials. Transpa... more This paper reports a methodology of half-embedding nanoparticles into metallic materials. Transparent and opaque nanoparticles are chosen to demonstrate the process of laser assisted nanoparticle embedding. Dip coating method is used to coat transparent or opaque nanoparticle on the surface of metallic material. Nanoparticles are embedded into substrate by laser irradiation. In this study, the mechanism and process of nanoparticle embedding are investigated. It is found both transparent and opaque nanoparticles embedding are with high densities and good uniformities.
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