Mechanical and Conductive Properties of Cu Matrix Composites Reinforced by Oriented Carbon Nanotubes with Different Coatings

Because of the dilemma that the current industrial Cu enhancement methods lead to a significant decline in conductivity and ductility, Cu matrix composites reinforced by oriented multi-walled carbon nanotubes (MWCNTs) were prepared through sintering, hot extrusion, and cold drawing. Before sintering, Ni, Cu, and Ni&Cu coatings were electroless plated on MWCNTs as the intermediate transition layer, and then they were mixed with Cu powder through a nitrogen bubbling assisted ultrasonic process. By analyzing the composition, microstructure, and formation mechanism of the interface between MWCNTs and the matrix, the influence and mechanism of the interface on the mechanical properties, conductivity, and ductility of the composites were explored. The results indicated that MWCNTs maintained a highly dispersed and highly consistent orientation in the Cu matrix. The coating on Ni@CNT was the densest, continuous, and complete. The Ni@CNTs/Cu composite had the greatest effect, while the Cu composite reinforced by MWCNT without coating had the smallest reduction in elongation and conductivity. The comprehensive performance of the Cu@CNTs/Cu composite was the most balanced, with an ultimate tensile strength that reached 373 MPa, while the ductility and conductivity were not excessively reduced. The axial electrical and thermal conductivity were 79.9 IACS % (International Annealed Copper Standard) and 376 W/mK, respectively.

Results of Studying Strain Relaxation in Steel 25Kh17N2B-Sh (25Х17Н2Б-Ш) and Copper М1 Using Annular Samples of Equal Bending Resistance

The paper introduces the research into stress relaxation of corrosion-resistant steel 25Kh17N2B-Sh (25Х17Н2Б-Ш) at temperatures of 20 and 100 °C, annealed copper M1 of two types --- soft and subjected to preliminary plastic deformation --- at a temperature of 20 °C, used in the manufacture of parts for butt joints of high-pressure pipelines. The research was carried out on annular samples of equal bending resistance according to the method of Oding. The study shows the action of temperature on the rate of stress relaxation in steel 25Kh17N2B-Sh (25Х17Н2Б-Ш), as well as the effect of preliminary plastic deformation of annealed copper on its relaxation characteristics, which is especially noticeable in the first hours after loading. As a result of the analysis of experimental data and by means of nonlinear regression, we determined the numerical values of the parameters of the equations used to describe the process of stress relaxation. Using the obtained expressions, we calculated and plotted the curves of stress relaxation in the materials under study. Furthermore, we compared the stress values calculated using the obtained relaxation model for steel 25Kh17N2B-Sh (25Х17Н2Б-Ш) at a temperature of 20 °C with the results of stress relaxation of a control sample from the same material, the test results of which were not used in the development of a mathematical model. The calculated data showed good similarity with the experimental data obtained on the test sample, which indicates the correct operation of the mathematical model

Influence of Rare Earth and Fe Addition on the Microstructure and Mechanical Properties of Al-B Alloy

In this study, changes in the microstructure, mechanical properties, and electrical conductivity of as-cast and as-extruded Al–B based alloys with the addition of Fe and rare earth (RE) were investigated. The melted aluminum alloy was maintained at 750 °C and then poured into a mould at 200 °C. Aluminum alloys were hot-extruded into a rod that was 12 mm in thickness with a reduction ratio of 39:1. The addition of Fe and RE resulted in the formation of Al11RE3 and Al3Fe intermetallic compounds and the area fraction of these inter-metallic compounds increased with increasing Fe and RE contents. As the amount of Fe and RE increased, the average grain size of the extruded Al alloy decreased to 798.6, 196.1, and 21.9 µm, and the high-angle grain boundaries fraction increased to 24.8, 27.9, and 60.7%. In the case of cast materials, low electrical conductivity was shown by porosity and fine casting defects. As the Fe and RE contents increased, the electrical conductivity of the extruded Al–B alloy decreased to 62.3, 59.6 and 55.0% International Annealed Copper Standard. As the Fe and RE content increased the ultimate tensile strength improved from 90.8 to 112.9 MPa which was attributed to the grain refinement and formation of Al11RE3 and Al3Fe intermetallic compounds by the addition of Fe and RE.

Layer-Thickness Dependence of Hardness and Local Bucking Behavior in Electrodeposited Ni-Co-Cu/Cu Multilayered Films

The effect of layer thickness on hardness and buckling behavior was investigated on Ni-Co-Cu/Cu multilayered films. The Ni-Co-Cu/Cu multilayered films were grown on annealed copper substrates by electrodeposition. We fabricated the multilayered films with various layer thicknesses ranging from 10 nm to 1000 nm. First, dependence of Vickers hardness on the Cu layer thickness was investigated. When the Ni-Co-Cu layer had the constant thickness of 75 nm and the Cu layer thickness was smaller than 75 nm, the hardness increased rapidly with decreasing Cu layer thickness. Subsequently, compressive tests were conducted on the multilayered films having the component layers ranging from100 nm to 1000 nm, where the hardness values did not change rapidly with layer thickness. The copper substrates coated with the multilayered films were compressed until 20% strain. From SEM surface observations after the compressive tests, formations of band-like structures having a certain thickness were recognized. Cross-sectional observation revealed that some band-like structures were formed as a result of local buckling of the multilayered film. The vertical thickness of the bank-like structures increased linearly with increasing component layer thickness.

Эффекты амплитудно-зависимого внутреннего трения в низкочастотном стержневом резонаторе из отожженной поликристаллической меди

Experimental and theoretical studies of the effects of amplitude-dependent internal friction in a low-frequency rod resonator made of annealed polycrystalline copper are carried out. The results of measurements of nonlinear losses and the shift of resonant frequencies at the first three longitudinal modes of the resonator in the kilohertz frequency range from 2 to 11 kHz are presented. The analytical description of the observed effects is carried out in the framework of the rheological model and the equation of state of a microhomogeneous medium with saturation of hysteresis losses and relaxation of its visco-elastic defects. From the comparison of experimental and analytical results, the values of the effective parameters of the hysteresis nonlinearity of the annealed copper sample and their dependence on the frequency are determined.

Microstructure and Properties of Copper–Graphite Composites Fabricated by Spark Plasma Sintering Based on Two-Step Mixing

The microstructure and properties of Copper-Graphite Composites (CGC) prepared by spark plasma sintering (SPS) based on two-step mixing and wet milling were investigated. The results showed that Cu powders were rolled into Cu flakes during milling, and their size significantly decreased from 23.2 to 10.9 μm when the graphite content increased from 1.0 wt.% to 2.5 wt.%. The oxidation of Cu powder was avoided during two-step mixing and wet milling. After spark plasma sintering, the graphite powders of the composites were mainly distributed at Cu grain boundaries in granular and flake shapes. The mean size of Cu grains was 9.4 um for 1.0 wt.% graphite content and reduced slightly with the increasing of graphite content. Compared with other conventional methods, the composite prepared by two-step mixing and SPS achieved higher relative density, electrical conductivity, and micro-hardness, which, respectively, reduced from 98.78%, 89.7% IACS (International annealed copper standard), and 64 HV (Vickers-hardness) to 96.56%, 81.3% IACS, and 55 HV when the graphite content increased from 1.0 wt.% to 2.5 wt.%. As the graphite content increases, the friction coefficient and wear rate of the composite decreases. When the graphite content of CGC is 1.0 wt.%, the main wear mechanism was plastic deformation, delamination, adhesive, and fatigue wear. The adhesive and fatigue wear disappeared gradually with the increasing of graphite content.

Automation of a copper wire manufacturing process using up-casting method – subsystem for induction heating

The aim of the research presented here is to design and implement a system for automatic production of copper wire, by the method of up-casting. The subsystem for induction heating includes automatic control of the temperature of the melted as well as annealed copper, automatic regulation of the induction heating power. The induction coil was designed and made to provide proper heating of the copper wire that is produced, so that the necessary temperature can be reached and its annealing or melting obtained. The coil is made of copper tube and its temperature is regulated using forced oil flow through the tube. The system can be easily adapted to be used in automation of the process of steel wire or iron wire annealing, having in mind the electrical and magnetic properties of the steel and iron. The system was produced, tested and put to work.

The Effect of Mn and Ca Addition on the Microstructure and Mechanical Properties of the Al–Cu–Fe–Si–Zn Based Alloys

High conductivity Al alloys are widely used for electric materials, heat exchangers, and heat dissipation parts such as electric conductors, transmission lines, communication cables, automobile wires and so on. In this study, the effects of Ca and Mn addition on the microstructure and mechanical properties of Al–0.3Cu–0.2Fe–0.15Si–0.15Zn alloys were investigated. The melt was held at 800 °C for 20 minutes and poured into a mold. The cast Al alloy was hot extruded with a rod having a diameter of 12 mm and a reduction ratio of 38:1. Al–0.3Cu–0.2Fe–0.15Si–0.15Zn–0.9Mn–0.4Ca alloy consists of Al, Al–(Fe, Mn)–Si, Al–(Fe, Mn) and Al–(Ca) intermetallic compounds. The formation of the intermetallic compound and this phase was broken in to small particles during extrusion. As the Ca content increased from 0 to 0.4 wt.%, the electrical conductivity of the extruded Al–0.3Cu– 0.2Fe–0.15Si–0.15Zn alloys increased by 57.3, 57.9 and 59.0 %IACS (International annealed copper standard). Al–0.3Cu–0.2Fe–0.15Si–0.15Zn–0.9Mn alloy with element additions of Ca, ultimate tensile strength was decreased from 178.3 to 163.2 and 151.8 MPa. However, the elongation was improved to 18.6, 21.6 and 23.15%.