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Multi-wall carbon nanotube (MWNT)-reinforced alumina composites were prepared by a sol-spray process combined with a vacuum hot press process. The relative densities of all the samples were higher than 97%. Scanning electron microscopy (SEM) results showed that the MWNTs were well-dispersed in the alumina matrix; specifically, most of them were distributed along the grain boundaries in the form of networks, whereas the others were located in the grains. For 0.5 wt.% MWNTs, the Vicker hardness and fracture toughness were 32.1% and 75.6% higher than those of pure alumina, and the average increment of the thermal diffusivity under different test temperatures is ~ 26.2%. When the content of MWNTs is higher than 0.5 wt.%, the composites showed conductor properties. Moreover, the percolation threshold of the prepared composites was 0.37 wt.% with the nonlinear fitting of conductivity data, which indicates that the MWNTs were well dispersed in the alumina matrix.

Strengthening effect of carbon nanotubes (CNTs) reinforced metal matrix composites (MMCs) mainly depends on the interfacial bonding strength which has a decisive influence on comprehensive properties of the composites. However, in CNTs reinforced Cu matrix composites, poor interface bonding due to the lack of wettability between CNTs and Cu matrix has become a bottleneck problem restricting the load-transfer capacity of CNTs. Different from the conventional thoughts of producing interfacial carbides by in-situ reaction with CNTs which will lead to deterioration of structural integrity of CNTs, a novel strategy is used by forming TiC on the surface of intact CNTs through solid phase reaction between the pre-milled CNTs and the Ti powders. The mechanical properties of the composites can be regulated by tailoring the morphology and amount of TiC decorated at the interface. Strong interfacial bonding achieved due to the specially designed interface structure which contributes to the dramatic improvement of strengthening efficiency of CNTs and benefits the plastic deformation of Cu matrix. Consequently, a simultaneous enhancement of tensile strength (281 MPa) and tensile elongation (20.1%) is achieved in the composite with TiC decorated at the interface, and a super high strengthening efficiency (135.8) is realized. The tactic used in our study can provide a reference for the preparation of other CNTs/MMCs.

Using high-efficiency bead milling dispersion technology, weakly agglomerated mixed nanoparticles were dispersed into a high solid content and low viscosity ITO slurry consisting of uniform single particles. The rheological properties of the slurry were studied as a function of the change in solid content and dispersant amount. The green ITO compacts with more uniform microstructure were prepared by mixing the slurry with high solid loading. Densification activation energies of the ITO compacts in different sintering atmospheres and different heating rate conditions were calculated by the MSC method based on shrinkage data. Finally, ITO ceramic targets with a grain size range of 3–6 μm were obtained by the two-step sintering method, and their phase structure was uniformly distributed.

In the development of copper-based composite materials, the dilemma of improving the mechanical properties without affecting the electrical properties is an important issue that must be solved. Here, carbonized polymer dot (CPD), as a novel reinforcement, was employed to fabricate CPD/Cu (pure copper) composite via powder metallurgy technique for the first time. The microstructure analysis revealed that the CPD was uniformly dispersed in the copper matrix in the form of nanoclusters, and the nanoclusters of CPD are composed of a three-dimensional amorphous carbon (AC) network structure and inserted carbon dots (some of them have a typical graphene structure, while others not). More importantly, excellent interface combination between the CPD and copper matrix is observed due to the existing of plenty of chemical functional groups. Based on this special microstructure, our prepared CPD/Cu composite achieves excellent mechanical and electrical conductivity simultaneously. Compared to pure Cu, the ultra-tensile strength of 0.2CPD/Cu composite is increased by about 17.0%, while the elongation is only ~ 2% lower. The electrical conductivity of the composite is ~ 98% IACS, which is much higher than that of pure copper prepared under the same condition (only ~ 92% IACS). New insights into how to prepare advanced copper matrix composites with simultaneously improved overall performance will be found from our research.

Pure Cu matrix composite reinforced by CrxOy-CNT hybrid was prepared via powder metallurgy in the present work. Microstructural analysis revealed that the formation of Cu2O nanoparticles at the interface is contributed to the interfacial bonding. The CrxOy-CNT/Cu composite of 1.0 vol% hybrid reinforcement exhibited excellent ultimate strength of 402.6 MPa, which was ~ 90.0% higher than that of unreinforced Cu (211.9 MPa). Meanwhile, the ultimate strength of the hybrid reinforcement was much higher than those of the separate components, which were 238.4 MPa of 1.0 vol% CNT/Cu composite and 339.1 MPa of 1.0 vol% CrxOy/Cu composite, respectively. Furthermore, the quantitative analysis indicated that Orowan looping system contributed the most to strength in CrxOy/Cu and CrxOy-CNT/Cu composites, whereas load transfer then contributed the most strength for CNT/Cu composite.

WC-6Co cemented carbide with super mechanical properties and excellent corrosion resistance was successfully prepared by optimizing Mo2C content. The structure, mechanical and anti-corrosion behaviors of cemented carbide were evaluated via a series of professional tests and measurements. The results revealed that the alloy phase of cemented carbide with various Mo2C contents was identical. Nevertheless, the content of Mo element in Co binder phase was higher than that in WC phase owing to the Mo2C dissolution in Co binder phase. The average grain size of WC displayed a downtrend after adding Mo2C additive. Differently, the Vickers hardness was increased after adding Mo2C additive and reached the maximum when the Mo2C content was 1.0%. In addition, the corrosion resistance of cemented carbide in 0.1 M HCl and NaOH solutions was improved by adding proper Mo2C additive. This was due to the synergistic effect of the optimized relative density, the modification of Co binder phase and the formation of passive film.

Alumina and zirconia ceramic particles exhibit high hardness and excellent wear resistance at high temperature, and hence are used as ceramic reinforcement phases in some plasma sprayed coatings. In this study, the interface evolution of a zirconia/alumina eutectic ceramic and the phase transition of zirconia in a plasma-sprayed coating were investigated. Scanning electron microscopy and transmission electron microscopy combined with focused-ion beam and energy dispersive X-ray were used to analyze the microstructure and composition of the ceramic interface. The results showed that the eutectic ceramic particles consisted of alumina (outer) and columnar zirconia (inner) before and after the plasma spraying process. The inner zirconia part showed the martensitic transformation of t-type zirconia to stripe-like m-type zirconia. After the plasma spraying, the interface between alumina and zirconia changed significantly, which formed a new oxide layer. The phase transition mechanism in the ceramic particle and oxide layer formation mechanism at the alumina/zirconia interface were investigated.

Aluminum (Al) matrix composites gain tremendous attention as candidates for lightweight structural materials. Interfaces between the matrix and reinforcements, long-standing concerns, are critical in determining the mechanical properties of Al matrix composites. Unlike the conventional thoughts that focus on raising the interfacial wettability, a novel interfacial nano-decoration strategy is reported to enhance the interfacial adhesion by forming a diffusion interface between Al and carbon nanotubes (CNTs) through copper (Cu) coating on the surface of CNTs. The resulted Cu-rich nanolayers through this strategy compromise the large interfacial misfit strain between Al and CNTs. Such unique interfacial structure improves the strengthening efficiency of CNTs and benefits the plastic deformation of the Al matrix, and thus contributes to a simultaneous increase in strength and ductility and breaks the ubiquitous strength-ductility trade-off dilemma in the structural material design. Consequently, we achieve an exceptional combination of tensile strength (391 MPa) and tensile elongation (15.7%) for our composite that surpasses its counterparts. The present tactic thus paves a new way to process high-performance Al matrix composites.

The intrinsic properties and the damage behavior of powder metallurgy (P/M) connecting rod preform have significant effects on its metal flow behavior during flashless forging into its final complex shape with substantial densification. The P/M material constitutive equation were established using isothermal compression tests, and then used to study the metal flow behavior of a P/M connecting rod preform during flashless forging based on finite element modelling (FEM). Moreover, the preform geometry was designed based on these metal flow mechanisms. Experiments and flashless forging of P/M connecting rod preforms were performed in order to verify the accuracy of the simulations. The simulated results are well consistent with the experimental results. Results showed that the shank is much more prone to cracking due to the higher deformation rate and the faster cooling rate. The optimal dimensions of the P/M preform were obtained. When the preform geometry are optimized, the average density of the connecting rod increases homogeneously, and becomes superior to that of the original shape. This work suggests that the geometry of the preform can be designed efficiently based on our models. This work can help to derive a P/M connecting rod preform optimization methodology, which can offer the possibility of improving the quality of the connecting rods efficiently. Keywords: Connecting rod, Numerical simulation, Optimization, Powder metallurgy

The density and phase structure uniformity of the IZO ceramic target would have an effect on the optoelectronic properties of the sputtered film. In this work, a uniformly dispersed IZO slurry was used to obtain high-density green IZO compacts by the slip casting process. Based on the grain size and shrinkage data of IZO ceramics, the densification process was investigated, while the apparent activation energy and growth activation energy were also calculated. The results of XPS showed that sintering in an oxygen atmosphere can increase the concentration of oxygen vacancies of IZO ceramic to improve its electrical properties. Finally, IZO ceramics with a grain size of 3-6 μm and resistivity of 1.5 mΩ·cm were obtained by a two-step sintering method.

Copper matrix composites with carbon nanotubes/Cu composite foams as the reinforcing skeletons (CNTs/Cuf®Cu) were prepared by electrodeposition and spark plasma sintering. The microstructure and tribological properties of the composites were studied. The CNTs reinforcements with the content up to 0.283 vol% remained uniformly distributed in the skeleton zone and led to quite different structure and properties as compared to the pure copper zone. Significant reduction of the friction coefficient and wear rate was shown with CNTs reinforcements in the skeleton up to a certain content. The wear surface morphology was analyzed and the possible wear mechanism was discussed for the composites with such an inhomogeneous structure.

Carbon nanotubes (CNTs) reinforced double-layered Cu-Ni composite foams (Cu-Ni/CNT foams) were prepared through chemical plating and electrodeposition, for the purpose of combining enhanced mechanical and electromagnetic shielding properties. The microstructure characterization revealed a quite uniform dispersion of the CNTs embedded in the metal layers, even after heat treatments. The property testing showed the compressive strength, energy absorption capacity and electromagnetic shielding effectiveness (SE) of Cu-Ni/CNTs foams were significantly improved, as compared to Cu-Ni foams. The heat treatments of the composite foams resulted in an interdiffusion of the Cu and Ni layers, causing an increase of compressive strength and a slight decrease of average SE. The possible mechanisms of the property evolution are discussed.

In this work, we investigated FeCrMo coatings with 35 wt% ceramic, which were produced on a cylinder surface by an internal rotating plasma spraying and oxidized in air. The ceramic particles consisted of 80 wt% alumina and 20 wt% zirconia, which can improve the mechanical properties of the coating. For microstructural characterization, scanning electron microscopy was combined with energy dispersive X-ray analysis and electron probe micro analysis, and the nanomechanical properties were measured by a nanoindentation tester. The structure of Fe-base coating matrix consists of Al 2 O 3 , ZrO 2 and a small amount of mixed Fe–Cr oxides, and the ceramic particles exhibit a uniform distribution. During oxidation, a mixed oxide layer containing Fe 2 O 3 and Fe 3 O 4 forms on the surface of the Fe-base coating, and the thickness of the oxide layer increases with increasing oxidation temperature. Due to the in-situ oxidation, the nanohardness and Young's modulus of the Fe-base coating decreased with increasing oxidation temperature. The nanohardness evolution of Fe-base coatings oxidized at different temperatures is discussed.

Novel core-shell-shell Fe@SiO 2 @(MnZn)Fe 2 O 4 soft magnetic composites (SMCs) with low core loss and high permeability were fabricated by a facile continuous chemical co-precipitation route and subsequent powder metallurgy technique. The typical double-shell structure for Fe@SiO 2 @(MnZn)Fe 2 O 4 powders was composed of a SiO 2 −(MnZn)Fe 2 O 4 mixed outer layer and an SiO 2 inner network embedded with trace amounts of (MnZn)Fe 2 O 4 . In comparison with Fe@SiO 2 SMCs, the Fe@SiO 2 @(MnZn)Fe 2 O 4 SMCs presented a notable flat high frequency characteristic up to 1 MHz, much higher permeability, and lower core loss which reduced with decreasing (MnZn)Fe 2 O 4 layer thickness. Fe@SiO 2 @(MnZn)Fe 2 O 4 SMCs prepared with 4 mL (MnZn)Fe 2 O 4 solution exhibited stable permeability of 64.0–63.5 up to 1 MHz and low core loss of 0.9–30.6 W/kg in 1–150 kHz. The strong magnetic coupling between the thin (MnZn)Fe 2 O 4 layer and Fe cores effectively reduced the air-gap thickness and demagnetization field giving rise to a high permeability. The low core loss could be attributed to the full separation of Fe core by thin dielectric−electrically insulating magnetic coupled with a SiO 2 /(MnZn)Fe 2 O 4 insulating layer. Our findings might shed insight on the design of novel SMCs with low core loss and high permeability.

Fe–Ni alloys with low thermal expansion coefficients were deposited on carbon fiber reinforced carbon matrix composite (C/C composite) as metallization coatings via ultrasound-assisted electrodeposition. The interface was compact at the micrometer scale, and the micro-cracks and pores on the composite surface were fully filled with the deposited alloy. The interface shear strength reached 16.24 MPa, which was a significant improvement in comparison with that of the conventional electrodeposition. These results may have been due to the residual stress reduction, the joining area increasement, and the pinning effect enhancement.

Copper foams reinforced by embedded Carbon nanotubes (CNTs) with uniform dispersion were prepared through composite electrodeposition on melamine foam templates. The microstructure, compression performance and electromagnetic shielding properties were characterized or tested by XRD, Raman, SEM, tensile tester and vector network instrument, respectively. The results showed significant improvements of the compressive strength, energy absorption and electromagnetic shielding properties of the composite foams with CNTs reinforcements, as compared to the copper foam counterparts. Such composite foams are potential light-weighted materials for shock resistance and electromagnetic shielding.

Nonuniform dispersion and weak interfacial bonding between carbon nanotubes (CNTs) and Cu matrix are two critical issues for achieving high strength and good ductility of CNT/Cu composites. Here, acid-treated CNTs precoated with Ni coatings were used to enhance the dispersion uniformity of CNTs and interfacial bonding between CNTs and Cu matrix in the CNT/Cu composites fabricated through spark plasma sintering and subsequently cold rolling. Scanning electron microscopy analysis revealed the homogeneous dispersion of Ni-coated CNTs (Ni-CNTs) in the composite compared with uncoated CNTs. Transmission electron microscope observation indicated that Cu2O nanoparticles were in situ formed at the interface in Ni-CNT/Cu composite, where CNTs were uncovered by Ni coatings. After rolling, the distribution of Ni-CNTs transformed into ribbons aligning along the rolling direction. The ultimate tensile strength (UTS) of 261 MPa was achieved in rolled 1 vol% Ni-CNT/Cu composite, which was 24.3% higher than that before rolling. The UTS of 2 vol% Ni-CNT/Cu composite obviously decreased, which could be attributed to the agglomeration of Ni-CNTs in the Cu matrix due to the increased volume content.

Strong interface bonding and effective load-transfer are the guarantees for developing high strength metal matrix composites (MMCs). Herein, the effect of residual oxygen in functionalized carbon nanofillers (CNFs) on the interface structure and the synergistic strengthening behavior of carbon nanotube-reduced graphene oxide (CNT-RGO) hybrids were investigated in Cu matrix composites. It was demonstrated that disordered areas and Cu2O nanoparticles were in-situ formed at the CNF Cu interface in the oxygen-poor and oxygen-rich areas through diffusion of oxygen, respectively. Cu2O was grown from the Cu matrix by means of cube-on-cube to obtain the minimum interfacial energy, under which equivalent planes and directions of Cu2O and Cu matrix are matched across the Cu2O Cu interface. A possible formation/evolution mechanism of the disordered areas and Cu2O involving oxygen content and sintering temperature was proposed. The ultimate tensile strength of 412 MPa was achieved in 1.5 vol% CNT-RGO/Cu composite sintered at 1023 K, which is significantly higher than that of CNT/Cu and RGO/Cu composites (231 and 263 MPa, respectively). Synergistic strengthening effect of CNT-RGO hybrids was investigated and analyzed based on strengthening models, and the trade-off between Orowan strengthening and load-transfer effect in CNF/MMCs was discussed to understand the synergistic strengthening behavior of CNT-RGO hybrids.

Carbon Nanotubes (CNTs)/Cu-Ti composites with strong interfacial bonding were successfully prepared by Molecular Level Mixing (MLM) combined with Spark Plasma Sintering (SPS) method. The relationship between interface evolution and mechanical properties was carefully investigated by High Resolution Transmission Electron Microscopy (HRTEM). It was found that three typical transition interfaces (Ti8C5, Ti8C5+TiC, TiC) were formed between the CNTs and the Cu-Ti matrix when 0.3 wt% CNTs/Cu-Ti composite powder was sintered at 1073 K for 10min, 20min and 30min respectively. Strong interfacial bonding and well-preserved CNTs structure were simultaneously realized in the sample which was sintered at 1073 K for 10min. The interface evolution phenomenon of the Ti8C5 to the TiC interface transition phase and a parallel orientation relationship ((219)Ti8C5//(111)TiC) were observed under a sintering time of 20 min at 1073 K. The 0.3 wt% CNTs/Cu-Ti composites sintered at 1073 K for 10 min exhibited yield strength of 368 MPa and tensile strength of 512 MPa, which were 59% and 51% higher than that of unreinforced Cu-Ti, 27% and 25% higher than that of 0.3 wt% CNTs/Cu composites without alloying. This study provides some new insights into the interfacial regulation of the CNTs/Cu composites with strong interfacial bonding and reinforcing effects.

Novel core@shell@shell structured carbonyl iron powder (CIP)@SiO2@ Mn0.6Zn0.4Fe2O4 ferrite composites having great microwave absorption characteristics were successfully synthesized using chemical co-precipitation. The microstructure, morphology and microwave absorption performance of CIP@SiO2@Mn0.6Zn0.4Fe2O4 ferrite composites were systematically investigated. The results show that both coating layers of SiO2 and Mn0.6Zn0.4Fe2O4 are uniform and fine. The prepared CIP@SiO2@Mn0.6Zn0.4Fe2O4 composites in this study display better dielectric loss and frequency characteristic at high frequency than CIP, CIP@SiO2 and CIP@Mn0.6Zn0.4Fe2O4. The results of electromagnetic parameters also indicate that the enhanced microwave absorption performance primarily originates from the substantial contributions of magnetic loss to reflection loss. The optimal value of reflection loss of CIP@SiO2@Mn0.6Zn0.4Fe2O4 having the thickness of 2 mm can reach up to −44.24 dB at 11.57 GHz as well as the bandwidth (RL ≤ −10 dB) from 9.04 to 16.16 GHz among the frequency range from 2 to 18 GHz. In addition, the greatly enhanced microwave absorption performance is attributed to good wave impedance matching, high attenuation constant, multi-relaxation processes and multiple interfacial polarization.

Carbon nanotubes-reinforced aluminum matrix (CNTs/Al) composites possess wide application prospects in many fields, and how to achieve a high performance is always a research hot spot. In this study, a novel high-performance Al matrix nanocomposite reinforced with short CNTs and in situ Al4C3 nanorods was fabricated by combining ball milling and hot extrusion, and they exhibit excellent comprehensive mechanical properties. The 2 wt% CNTs/Al composite reached a tensile strength of 312 MP and an elongation of 15.8%, showing an 102% strength improvement compared with the pure aluminum prepared by the same process. The remarkable improvement of the mechanical properties originates from the synergistical enhancement of fine-grained strengthening and dispersion strengthening of in situ Al4C3 nanorods and short CNTs.

In this paper, in situ Al4C3 and carbon nanotubes (CNTs) hybrid-reinforced aluminum matrix composites were prepared by a two-step ball milling (TSBM), consisting of a 24-h long-time ball milling (LTBM) and a 6-h short-time ball milling (STBM). During LTBM, most of the CNTs were seriously damaged, and many amorphous carbon atoms derived from these damaged defects would react with Al powder to form in situ Al4C3 nanorods. Subsequently, 1 wt% CNTs were added into the composite powders for STBM to uniformly disperse CNTs into the composite powders. Compared with that of the composite prepared by one-step ball milling, the comprehensive mechanical properties of the composite prepared by the TSBM are improved obviously due to the synergistic effects of in situ Al4C3 and CNTs, and the tensile strength and elongation reached 258 MPa and 19.5%, respectively. The strengthening mechanisms of TSBM composite include fine-grained strengthening, dispersion strengthening by in situ Al4C3, and load transfer from matrix to CNTs.

Silver composites with an inhomogeneous structure have been designed and prepared through spark plasma sintering (SPS) with carbon nanotubes reinforced Cu foams (CNTs/Cuf) as the reinforcing 3-dimentional skeletons. The composites simultaneously exhibit enhanced strength, good ductility and high conductivity, with the ultimate tensile strength (UTS) of 198.8 MPa, the fracture elongation of 38.5% and electrical conductivity of 98.53% IACS, respectively. After subsequent heat treatments, diffusion layers have formed with the thickness of about 10 μm at the interface between skeletons and the silver matrix, causing further improvements of the UTS and slight reduction of the ductility and conductivity. The structures, properties and possible mechanisms of the composites are studied and discussed in this paper.

The combination of active materials and carbon nanotubes (CNTs) provides an effective way to enhance battery capacity and optimize cycle performance. In the present study, the powder electrodeposition technology is employed to synthesize the NiO-Ni/CNTs composite for the first time. This technique contains the following steps. The CNTs are negatively charged by pre-discharge in lithium-ion batteries. Then, the negatived CNTs are uniformly dispersed in the NiCl2 plating solution by electrostatic repulsion, and the Ni ions are in situ reduced and deposited onto the CNTs. The close combination of CNTs and NiO-Ni improves the overall conductivity and structural stability. As electrode of lithium-ion battery, the reversible capacity is improved due to the coordination of the Ni metal in the mixture of the composite electrode. Besides, the reversible capacity of the composite electrode is 851 mAh g-1 at 50 mA g-1 after 50 cycles. The “Powder Electrodeposition” method in the current work provides a new way for the preparation of other similar powder composite materials. Furthermore, the problem that the traditional electrodeposition process is difficult to apply in the powder materials will be solved.

Silica/Cu composites generally fail to achieve the high strength due to the weak interfacial bonding between SiO2 and Cu. In the current work, the first use of silica quantum dots (SiO2 QDs) as a copper-based composite reinforcement. Silicon quantum dots (Si QDs) and copper acetate are employed as raw materials for spray pyrolysis to obtain an interconnected structure of SiO2 QDs/Cu2O, which achieve well-dispersion of the reinforcement and good interface combination in one step. The SiO2 QDs/Cu2O composite block is obtained by ball milling, hydrogen reduction, and SPS sintering. Micro interface structure and strengthening mechanism of the composites are investigated and presented in detail. Microstructural analysis discovers the Cu2O transition layer between SiO2 QDs and Cu matrix and well-dispersed SiO2 QDs in the Cu matrix. The good bonding of grain interface can significantly enhance the mechanical properties. The 1.2 wt% SiO2 QDs/Cu composite block exhibits an excellent ultimate tensile strength of 456.63 MPa, which is 101.68% higher than that of unreinforced Cu (227.39 MPa). Furthermore, the composite block maintains the high conductivity (83.27% IACS) and elongation (8.86%). Moreover, this work can promote the development of Cu matrix composites using ceramic reinforcement with an improved interface bonding.

Uniform dispersion and suitable interface are two critical issues to realize the high strengthening potential of carbon nanotubes (CNTs) in metal based composites. In this work, surface modification of CNTs was applied to simultaneously overcome these two challenges in Al matrix composites by a chemical oxidization method. It was found that the functional groups, such as hydroxyl and carboxyl groups, can be successfully decorated on the surface of CNTs by chemical oxidization, thus improving the dispersion of CNTs in ethanol. Concurrently, the morphology of oxidized CNTs and the Al-CNTs interface depend strongly on the activity of the applied oxidants. The mixture of sulphuric acid and hydrogen peroxide can slightly etch the outer walls of CNTs, which benefits the anchoring bonding between the CNTs inner walls and Al matrix, and improves the interface stability, hence exploits the load bearing capacity of the CNTs inner walls and eventually leads to the effective load transfer between Al and CNTs. The outstanding reinforcing effect of surface-modified CNTs was investigated and discussed by the strengthening models. This work provides a new approach to uniformly disperse CNTs and improve interfacial bonding for CNTs reinforced composites simultaneously.

The strengthening effects in nano-/ultrafine-grained carbon nanotube reinforced-titanium (CNT/Ti) composites are investigated based on the dislocation punched zone (DPZ) model from two aspects: CNT reinforcement and matrix grain refinement. Considering the geometrically necessary dislocations constrained in DPZs, the CNT/Ti composites are treated as three-phase composites consisting of CNTs, the DPZs, and the pure matrix. By using the Clyne method, the overall true stress–true strain relations of the CNT/Ti composites are predicted by finite element modeling. The predictions agree well with the experimental results. Then, the influences of the diameter, the aspect ratio, and the volume fraction of CNTs, as well as the matrix grain size, on the strengthening mechanisms in CNT/Ti composites are investigated. The results show that the grain refinement of the matrix increases the overall strength and simultaneously decreases the thermal expansion mismatch strengthening induced by CNTs. It can be concluded that the strength of CNT/Ti composites can be enhanced by increasing the aspect ratio and the volume fraction of CNTs, as well as by decreasing the matrix grain size and the diameter of CNTs. This work presents a method to easily allow the use of readily available finite element software to obtain the overall mechanical response of composites and helps to design composites with excellent mechanical properties.

Carbonyl iron powder (CIP) and reduced iron powder (RIP) were homogeneously coated with an SiO2 insulating layer by a controlled in-suit chemical deposition procedure and used as raw materials to fabricate CIP/SiO2-RIP/SiO2 (C-R) soft magnetic composites (SMCs) by powder metallurgy techniques. Compared with RIP/SiO2 powders, CIP/SiO2 powders possess a higher SiO2 content and more stable Si-O covalent network. The addition of CIP/SiO2 to the C-R SMCs leads to a significantly increase in the resistivity due to the full electrical isolation of the RIP/SiO2 particles. Transmission electron microscopy analysis confirms that a SiO2 amorphous layer approximately 100–400 nm in thickness grows with a high packing density and adheres tightly to the iron grains, resulting in the effective constraint of electron transfer between the Si and O atoms. Annealed C-R SMCs containing 15–20 wt% CIP/SiO2 have optimum properties with a high resistivity of 4980–6383 μΩ·m and a low core loss of 19.08–23.66 W/kg (50 mT, 100 kHz). The results of this present study provide a significant method to improve resistivity and reduce core loss.

Interface between carbon nanotubes (CNTs) and copper matrix is generally weak mechanical bonding due to the lack of wetting and interaction between them. In the present study, the homogeneous distribution of CNTs in copper matrix was realized through a novel mixing method and spark plasma sintering (SPS). The interface structures of CNTs/Cu composites were optimized by using decorated CNTs. Transmission electron microscopy (TEM) observation revealed the formation of interfacial products, amorphous transition areas and interfacial stress zones at the decorated-CNT/Cu interfaces. The compressive tests showed that the composite containing 2 vol% of Ni-coated CNTs has a maximum compression yield strength of 554 MPa, which was increased by 55% and 30% compared with that of pure Cu and the composite reinforced with pristine CNTs, respectively. The strong strengthening effects of the decorated CNTs can be attributed to their interaction with Cu matrix. The strengthening mechanisms, load transfer efficiency and interfacial shear strength were also discussed from the point of interface structure. This work underscores the importance of the surface state of CNTs on the interface structure in metal matrix composites, and may provide insights into the composites where reinforcements and matrix are lack of wetting and interactions.

In this work, the effects of aluminum carbide (Al4C3) on the mechanical properties and thermal behaviors of Al based composites reinforced by SiC and carbon nanotubes (CNTs) were investigated. The formation of Al4C3 was precisely controlled in the temperature range from 530 °C to 630 °C (80%–95% of the Al melting point) during the post heat treatment. Microscopy observations revealed that Al4C3 rods are originated from CNTs instead of SiC particles. Quantity and size of Al4C3 are highly dependent on the heat treatment temperature. It was found that the mechanical properties of the Al based composites were significantly affected by the size of Al4C3. Moreover, the formation of Al4C3 helps to decrease the coefficient of thermal expansion (CTE) of the composites due to the consumption of Al and the enhanced interfacial bonding. This study provides a potential approach for ameliorating the mechanical and thermal performances of CNTs reinforced metal matrix composites.

Acquiring metal matrix composites with high strength and large ductility simultaneously is a critical issue, which determines their potential applications in industrial field. In this study, we reported that the well balanced high strength and ductility of Cu/CNTs composites can be achieved by combined effects of full densification, uniform dispersion of CNTs, strong interfacial bonding and suitable Cu matrix features. The interfacial bonding in Cu/CNTs composites is highly dependent on the sintering temperature and CNTs content. The related strengthening and toughening mechanisms were discussed according to the microstructure and related model. This study provides a new insight in fabricating CNTs-reinforced metal matrix composites with high strength and large ductility.

In this study, a novel mixing method that combines wet mixing and conventional ball milling followed by spark plasma sintering (SPS) was used to fabricate carbon nanotube (CNT)-reinforced Cu-matrix composites. The samples were characterized using scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray diffraction. In the CNT/Cu composites produced, the CNTs were uniformly dispersed whilst maintaining their integrity. Consequently, a combination of high strength, ductility, and electrical conductivity was achieved by a 2.5 vol% CNT/Cu composites (ultimate tensile strength 280 MPa, elongation 41.7%, and electrical conductivity (IACS%) 91.6%). These results could potentially be used to effectively ameliorate the issue of strength-ductility and strength-conductivity trade-offs in metal-matrix composites.

In this paper, effect of dispersion state of carbon nanotubes (CNTs) on electrical conductivity of copper (Cu)-matrix composites was investigated. While, it is interestingly found that composite with homogeneous dispersion CNTs has the lowest electrical conductivity (90.47 ± 0.34 IACS% (International Annealed Copper Standard)) and that one with aggregation CNTs has the best conductivity (93.45 ± 0.17 IACS%). This phenomenon was attributed to interconnected conductive networks of Cu damaged by adding dispersed CNTs through interface scattering between CNTs and Cu. Thus, it can be concluded that the dispersion of CNTs is not the key point to obtain high electrical conductivity of CNT/Cu composites.

Mono-dispersed and homogeneous carbon nanotube (CNT)/copper (Cu) composite powders were fabricated by spraying pyrolysis (SP) method successfully. Subsequently, CNT/Cu composites were obtained by spark plasma sintering (SPS) at sintering temperature ranged from 1023 to 1223 K (70–90% melting point of pure Cu). The mechanical properties, micro-morphology and interface microstructure of CNT/Cu composites were measured and characterized. The results reveal that Cu nano-particles (NPs) coated on the CNT surface are conducive to improving the wettability of CNT within matrix and reducing the interface energy between matrix and CNT, and finally stable interface structure is established. The traditional trade-off tendency between strength and ductility is balanced in the CNT/Cu composites, which are sintered at 1223 K. The ultimate tensile strength (UTS) shows 344 MPa and the elongation is 19.6%, which owing to the improvement of CNT–Cu interface bonding. At last, the role of interfacial bonding extent played in determining the load transfer efficiency of CNT is discussed.

Functionally graded materials (FGM) are a group of promising materials but demand efficient and reliable manufacturing approaches. We report a novel method utilizing microwave (MW) processing to fabricate functionally graded W/Cu composites. In the present work, the MW sintering set-up was designed to allow a potent heat flux and significant thermal gradient during the sintering. W skeletons with porosity gradient were synthesized first by using MW selective sintering. The W skeletons were subsequently infiltrated with Cu and W-Cu compositional graded composites were obtained. Corresponding to the compositional gradient, the composites showed gradients in hardness and electric conductivity. In addition, the graded microstructure and composition can be tailored by adding sintering activator such as Ni. This route provides an effective fabrication method of both porosity-gradient and compositional graded materials W/Cu composite.

Nano-/ultrafine-grained carbon nanotube-reinforced titanium (CNT/Ti) composites were synthesized by ball milling and high pressure torsion (HPT) at room temperature. The effects of the number of HTP rotations and the weight fraction of CNTs on the microstructure, hardness and tensile properties of the CNT/Ti composites were investigated. Transmission electron microscopy (TEM) revealed that elongated grains with an average length of 100–250 nm parallel to the compression axis of HPT and a thickness of 10–25 nm are formed in CNT/Ti composites when CNT contents ranging from 0.3 wt% to 1.0 wt%. With increasing CNT contents, the grain size of Ti is refined, and the microhardness and tensile properties of the composites increase. Evaluating the mechanical properties of the CNT/Ti composites with 0.7 wt% CNTs after 20 rotations indicates a high tensile strength of 872 ± 5 MPa. Cs-corrected high resolution TEM of the interfaces between Ti and the CNTs after HPT reveals a gradual transition from the lattice planes of hexagonal Ti to those of the CNTs. The strengthening mechanisms are discussed from the aspects of matrix grain refinement, distribution of the CNTs and the CNT-Ti interfaces obtained during ball milling and HPT processing.

Carbon nanotubes reinforced silver composites (CNTs-Ag composites) are considered as a promising candidate for high-performance contact materials with the potential properties of low contact resistance, high thermal conductivity and excellent mechanical performance. While at present the dispersion of CNTs in silver matrix and the interfacial bonding of the composites remain problems to be resolved or enhanced. In this study, silver nanoparticles coated carbon nanotubes (Ag@CNTs) were synthesized through an improved electroless plating method assisted by ultrasonic spray atomization, which inhibited excessive growth of silver particles and led to much more uniform nanometer grain-sized coating. The Ag@CNTs were solution ball-milled (SBM) with Ag powders and then were densified by spark plasma sintering (SPS). The composites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS). The results showed the CNTs dispersion in Ag matrix was improved benefitting from the homogeneous Ag nanoparticles distribution on CNTs, and correspondingly, the hardness and electrical conductivity were significantly improved. The mechanism may result from the combination of more homogeneous CNTs dispersion and tighter interface bonding in composite materials.

Unique architecture of reinforcement is explored for developing advanced metal matrix composites (MMCs). In the present study, Cu matrix composites reinforced by carbon nanofillers with reticulate structure were prepared by powder metallurgy. It was found that the high-efficiency strengthening effect was achieved by employing the hybrids of carbon nanotubes (CNTs) and reduced graphene oxide (RGO) as reinforcements in the Cu matrix. The tensile test results showed that the ultimate tensile strength of ~ 409 MPa was achieved in Cu matrix composite with 1.5 vol% of CNT-RGO hybrids, which is significantly higher than that reinforced with individual CNTs or RGO (~ 226 and ~ 259 MPa, respectively). Strengthening mechanisms including grain refinement, generation of dislocations by thermal mismatch, load transfer and Orowan looping system were discussed to understand the strengthening behaviors of CNT-RGO hybrids in MMCs. This work underscores the importance of interconnected architecture of reinforcements for improving mechanical properties of the composites and provides an insight to understand the strengthening behaviors of reticulate reinforcements in the composites.

By hybridizing carbon nanotubes (CNTs) into SiC reinforced Al matrix composites, a novel composite was fabricated to achieve excellent mechanical properties and low coefficient of thermal expansion simultaneously. The study demonstrated that the CNTs can help to acquire the uniform dispersion of SiC particles in the Al matrix, because of their interaction during ball milling and hot rolling processes. In addition, the results revealed that such design optimizes both the mechanical and thermal properties, due to homogeneous microstructure as well as tight and uniform interfaces induced by the addition of CNTs. Strengthening mechanism and Sideridis's model were used to discuss the effects of the CNTs on the mechanical and thermal properties. This study opens up an unexplored avenue for simultaneous improvement of the mechanical and thermal properties of metal matrix composites.

Cu/buckypaper composites were prepared through electrodeposition of Cu onto buckypaper from a Cu sulfate electrolyte. The oxygen-containing functional groups were introduced to the surface of carbon nanotubes (CNTs) through acidification and oxidation. Incorporation of functional groups was shown to facilitate the spontaneous reduction of Cu ions on the surface of CNTs during immersion treatment. Under small deposition current density of 1 mA cm−2, Cu ions could penetrate into the reticulate structure of buckypaper and nucleate homogeneously on the CNTs, which led to the formation of a thicker transition layer. Functionalization also increased the nucleation rate of Cu on the CNTs. When the current density was 1 mA cm−2, the electrical conductivity of Cu/oxidized buckypaper composite reached the maximum value of 4.09 × 105 S cm−1 which was 76% of pure Cu. The ampacities of all the composites were obviously improved compared with electrodeposited pure Cu. The Cu/oxidized buckypaper composite had the maximum ampacity of 15437 A cm−2, which was 65% and 14% higher than that of pure Cu and Cu/original buckypaper composite, respectively. Good interface bonding and reticulate structure of CNTs formed in the transition layers are responsible for the relatively high electrical conductivities and high ampacities of Cu/buckypaper composites.

The poor dispersion of carbon nanotubes (CNTs) in a copper matrix and the weak interfacial bonding between CNTs and the Cu matrix critically hinders the engineering applications of their composites. Herein, we obtained a well-dispersed and tight interfacial bonding between CNTs and Cu matrix in the Cu/CNTs composites fabricated via spark plasma sintering and subsequently hot rolling. Microstructural characterization shows that the small grain size of Cu matrix, the uniform dispersion of CNTs, and the good wettability and interfacial bonding between the CNTs and Cu significantly improved the mechanical properties of the Cu/CNTs composite. This work provides an innovative fabrication process for the development of high performance Cu/CNTs composites with excellent interfacial bonding strength.

Microlaminated carbon nanotubes (CNTs) reinforced Cu matrix composites were prepared by combination of composite electrodeposition and spark plasma sintering (SPS). Interdiffusion transition regions formed between CNTs and Cu matrix under high sintering temperature, which were responsible for the balanced strength and ductility of the composites.

Carbonized polymer dots/copper (CPD/Cu) composites were successfully prepared by a powder metallurgy process. An exhaustive comparison with reduced graphene oxide (RGO)/Cu and carbon nanotubes (CNT)/Cu composites in terms of properties, microstructure and strengthening mechanism reveal the simultaneous increase in strength and toughness of the CPD/Cu composite, which is mainly due to the CPD structure in the form of “nano-CPD ball with shell”. Meanwhile, an obtained transition area can perfectly solve the problem of dispersion and interfacial bonding of carbon reinforcements in the Cu matrix. Our results cast a new light on preparation and development of carbon nanomaterial/Cu composites.

Copper (Cu) matrix composites reinforced with 0.3, 0.5, 1.0, and 2.0 vol% multi-wall carbon nanotubes (MWCNTs) were processed by ultrasonication and high-energy attritor milling of pure copper powder with carbon nanotubes (CNTs), followed by spark plasma sintering and annealing. Microstructural characterization shows that the CNTs are well-dispersed in Cu-0.5 vol% CNTs composite, and the aggregation of CNTs increases with the increase in the volume fraction of carbon nanotubes. Raman spectroscopy results indicate that there is an increase in the number of defects in the nanotube after milling and sintering of the composite. Mechanical property and strengthening mechanism analysis indicates that the grain size effect, hindering effect of dislocations interacting with the grain boundary, and load transfer effect are the main mechanisms affecting the mechanical properties of composites, and the experimental strength of the composite can be close to 81% of the theoretical strength.

Micron-sized CNTs/Cu 2 O composite powder prepared by Molecular Level Mixing (MLM) was mixed with flaked Cu-1.0 wt% Ti (Cu-1.0 Ti) matrix powders by low-energy ball milling. After reduction and hot pressing, CNTs/Cu-Ti composites were fabricated. Microstructure and mechanical properties of the composites were characterized by SEM, EDS, HRTEM, hardness and tensile tests, etc. The results showed that mechanical properties of the CNTs/Cu-Ti composites were enhanced compared with alloy matrix, which were ascribed to the well-distributed of CNTs and strong bonding interface with the matrix by the formation of a transition layer of TiC. Finally, strengthening mechanisms were discussed.

Inspired by cocklebur's design principle, an innovative three-dimensional (3D) interface design was proposed to strengthen the interface bonding of graphene nanoplatelets reinforced Ti matrix composites (GNPs/TiMCs). To elucidate the growth mechanisms of in-situ TiB array with oriented assignment configuration, the novel pressureless spark plasma sintering (PL-SPS) followed by heat treatment (HT) were performed on the TiB2@GNPs/Ti powders. It was found that TiB nanocrystals epitaxially grown at GNPs wrinkle sites with typical orientation relationship of TiB (101)//GNPs (200), as determined by the nanobeam diffraction mode of TEM. Moreover, the special symbiosis structure between in-situ TiC and TiB was also observed in the growth densification stage, which was beneficial for the TiC-TiB bonding. Finally, the heteroepitaxial mechanism of TiB has inspired the 3D interface configuration in bulk GNPs/Ti, and simultaneously enhanced strength and ductility were achieved as compared to the conventional GNPs/Ti composites.

Carbon nanotube-graphene (CNT-GP) hybrids are directly synthesized on the surface of Cu powders through CVD by using Cu as both the catalyst and metal matrix. The sintered composites show a good combination of strength and ductility, which can be attributed to the interconnected architecture of chemically hybridized CNT-GP hybrids.

Strength and ductility are often a paradox in carbon nanotubes (CNTs) reinforced Cu matrix composite, as well as strength and electrical conductivity. Interface and characteristics of CNTs are critical factors in determining the mechanical properties and conductivity of Cu matrix composites. In the present study, a novel tactic by surface and intratube decoration of CNTs is adopted to break the above mentioned dilemmas. By decorating the surface of CNTs with CuO nanoparticles and taking advantage of the good wettability between CuO and Cu matrix, uniform dispersion of CNTs is realized through ball milling. In the final composite, CuO nanoparticles on the surface of CNTs are reduced to Cu. High density interfacial dislocations and interfacial disordered areas are formed between Cu matrix and CNTs, thus forming a strong interfacial bonding. By decorating the inner walls of CNTs with Cu nanoparticles, the interfacial shear stress between Cu matrix and CNTs is improved due to the extrusion effect of Cu nanoparticles on the inner walls. Moreover, the Cu filled inside the tubes can also reduce the intra-tube resistivity of CNTs by increasing their conducting cross-section. Consequently, the Cu matrix composite with simultaneous improvement of strength (272 MPa), ductility (14.3%) and conductivity (93.6% IACS) is achieved in our present study. This tactic provides a new idea to deal with the strength-ductility and strength-conductivity dilemmas in CNTs reinforced metal matrix composites.

Carbon nanotubes reinforced pure aluminum (CNT/Al) composites were fabricated by combined ball milling and powder metallurgy (PM) techniques. The distribution of CNTs, the evolution of the average Al grain size of the powder mixtures and as-prepared composite bulks were investigated, and the mechanical properties of the composites were also tested. With increasing ball milling time, the entangled CNTs were broken, gradually achieving a uniform dispersion within the Al matrix. The microstructure became denser and the Al grains in the powder mixture and extruded composites got significantly refined. Some small-sized Al 4 C 3 needles along the Al grain boundaries were observed using transmission electron microscopy (TEM). The in-situ formed Al 4 C 3 rods have an orientation relation with the Al matrix as Al 4 C 3 [110]//Al [ 1 ¯ 12 ], which strongly improved the Al-CNT interface bonding. The yield and the ultimate tensile strength of the composites significantly increased, when the ball milling time increased from 2 to 12 h, finally reaching about 210 ± 4.2 MPa and 253 ± 3.7 MPa, respectively, for the composite milled for 12 h. The enhancement of mechanical properties mainly stems from the uniform distribution of CNTs, the grain refinement of the Al matrix and the in-situ formed Al 4 C 3 .