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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

Carbon nanotube reinforced titanium (CNT/Ti) composites with high tensile strength (872 ± 5 MPa) were synthesized by the high pressure torsion process (HPT). Cs-corrected high resolution transmission electron microscopy (TEM) revealed face centered cubic titanium (FCC–Ti) distributed in the grains and at the grain boundaries of a hexagonal close packed titanium (HCP–Ti) matrix, with an orientation relationship of [0002]HCP//[11 1 ¯ ]FCC and {2 1 ¯ 1 ¯ 0}HCP//{011}FCC between FCC-Ti and HCP-Ti. The phase transformation from a HCP-Ti structure to a FCC-Ti structure in the CNT/Ti composites during the HPT process made a significant impact on the mechanical properties. Combining experimental results with density functional theory calculations, the stability of FCC-Ti and HCP-Ti under external pressure were analyzed. Moreover, the nucleation and growth mechanisms of FCC-Ti phase in HCP-Ti matrix were identified. The results showed that the stress-induced phase transformation from HCP-Ti to FCC-Ti in the CNT/Ti composites during the HPT process is associated with the source of Shockley partial dislocations. This work helps to the better understanding of the phase transformation mechanism from a HCP-Ti structure to a FCC-Ti structure in CNT/Ti composites.

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.

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.

B2 CuZr exhibits a stress-induced martensitic transformation from a B2 to a B19 structure during tensile deformation, and that is believed to be the reason for the pronounced ductility and work hardening of CuZr-based bulk metallic glass (BMG) composites. In order to gain a better insight into the structural transformation of CuZr precipitates, the phase stabilities as well as the anisotropic elastic and thermodynamic properties of both B2 cubic (CsCl-type) CuZr and B19 (β-AuCd-type) CuZr structures under hydrostatic pressures up to 30 GPa are investigated by first principles calculations. Moreover, the effects of the hybridization between the electronic orbitals of the constituent atoms on the variation of the elastic properties of the B2 CuZr structure are discussed. The results show that the Young's modulus (E), bulk modulus (B) and shear modulus (G) increase significantly with increasing pressure. Noticeably, for pressures up to 30 GPa, the B2 CuZr structure shows a stronger anisotropy along the (1 1 0) plane than for the (1 0 0) plane. Under high pressure, the stability of both B2 CuZr and B19 CuZr phases decrease while the Helmholtz free energy (F) and the formation enthalpy (H) of B2 CuZr increase monotonically. However, the different stability decreasing trajectories of both B2 and B19 CuZr phases result in a high propensity of martensitic transformation from the B2 to B19 structure. Our results may have implications for better understanding the phase stability of B2 and B19 CuZr structures under high pressure and can shed light on the structure-property relationships of BMG composites reinforced with shape-memory crystals.

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.

Powder forged connecting rods have the problem of non-uniform density distributions because of their complex geometric shape. The densification behaviors of powder metallurgy (PM) connecting rod preforms during hot forging processes play a significant role in optimizing the connecting rod quality. The deformation behaviors of a connecting rod preform, a Fe-3Cu-0.5C (wt pct) alloy compacted and sintered by the powder metallurgy route (PM Fe-Cu-C), were investigated using the finite element method, while damage and friction behaviors of the material were considered in the complicated forging process. The calculated results agree well with the experimental results. The relationship between the processing parameters of hot forging and the relative density of the connecting rod was revealed. The results showed that the relative density of the hot forged connecting rod at the central shank changed significantly compared with the relative density at the big end and at the small end. Moreover, the relative density of the connecting rod was sensitive to the processing parameters such as the forging velocity and the initial density of the preform. The optimum forging processing parameters were determined and presented by using an orthogonal design method. This work suggests that the processing parameters can be optimized to prepare a connecting rod with uniform density distribution and can help to better meet the requirements of the connecting rod industry.

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.

Copper vanadate materials have a higher gravimetric capacity and energy density than those of the traditional vanadium oxide or vanadate electrodes because of the multistep oxidation-reduction reactions. This work presents the synthesis of nano-structured copper vanadates using ion-exchange reaction of sodium vanadate nanowire arrays in an aqueous solution, containing copper acetate or copper nitrate. The morphology, crystal structure, composition and lithium-storage performance of the materials are measured and characterized thoroughly. Due to the dissolution effect of the acetate anion on the sodium vanadate nanowire arrays, copper vanadate spheres composed of nanosheets are produced. By contrast, after the ion-exchange reaction in the copper nitrate solution, the sample maintains its original nanowire arrays structure. The copper vanadate nanowire arrays synthesized in copper nitrate solution for 48 h followed with calcination at 300 °C for 2 h exhibit a remarkably high storage capacity of up to 997.76 mAh g−1 in 3–0.01 V versus Li/Li+, thus showing a great potential for application in lithium-ion batteries.

Powder-forged connecting rod with a complex geometry shape always has a problem with nonuniform density distribution. Moreover, the physical property of preform plays a critical role for optimizing the connecting rod quality. The flow behavior of a Fe-3Cu-0.5C (wt pct) alloy with a relative density of 0.8 manufactured by powder metallurgy (P/M, Fe-Cu-C) was studied using isothermal compression tests. The material constitutive equation, power dissipation (η) maps, and hot processing maps of the P/M Fe-Cu-C alloy were established. Then, the hot forging process of the connecting rod preforms was simulated using the material constitutive model based on finite element method simulation. The calculated results agree well with the experimental ones. The results show that the flow stress increases with decreasing temperature and increasing strain rate. The activation energy of the P/M Fe-Cu-C alloy with a relative density of 0.8 is 188.42 kJ/mol. The optimum temperature at the strain of 0.4 for good hot workability of sintered Fe-Cu-C alloy ranges from 1333 K to 1380 K (1060 °C to 1107 °C). The relative density of the hot-forged connecting rod at the central part changed significantly compared with that at the big end and that at the small end. These present theoretical and experimental investigations can provide a methodology for accurately predicting the densification behavior of the P/M connecting rod preform during hot forging, and they help to optimize the processing parameters.

A novel carbonized polymer dots (CPD)/copper (Cu) composite was successfully synthesized via molecular level mixing (MLM) and spark plasma sintering (SPS) process. Microstructure analysis shows that the CPD clusters are well dispersed at the Cu grain interfaces by forming an amorphous carbon (AC) network with a large number of inserted graphene carbon dots (some of them show the typical graphene microstructure). Mechanical properties of the CPD/Cu composite are remarkably higher than that of pure Cu sample, which increases initially with CPD wt.% and then decreases. 0.4 wt% CPD/Cu composite obtains ~47% higher strength than that of pure Cu matrix. Meanwhile, the thermal conductivity is improved from 305 W/m·K to 360 W/m·K without any adverse impact on the mechanical properties. This study provides new insights into the preparation of the advanced Cu composite with enhanced comprehensive performance.

As a hybrid reinforcement, interconnected architecture of carbon nanotubes (CNT)/Tungsten (W) composite powder was designed and fabricated by spraying pyrolysis (SP) method. Subsequently, CNT-W/copper (Cu) composites were fabricated successfully by low energy ball milling (LEBM) and spark plasma sintering (SPS). The electronic conductivity, mechanical properties, micro-morphology and interface microstructure of CNT-W/Cu composites were evaluated and characterized. The results revealed that CNT with attached W were dispersed uniformly in the Cu matrix and W particles played a “pinning” role of the CNT. The 0.6 wt%CNT-W sample exhibited ultimate tensile strength 226 MPa and the elongation 33%, which were 14% and 83% higher than that of pure Cu, respectively. Besides, the 0.8 wt% CNT-W sample exhibited electrical conductivity 92.3%IACS, which is very close to that of Cu matrix (92.6%IACS). Finally, the strengthening and electric conductivity mechanisms of CNT-W in Cu matrix were considered. This study inspires a new way of synergistically reinforced metal matrix composites.