Performance and surface alloying characteristics of Cu–Cr and Cu–Mo powder metal tool electrodes in electrical discharge machining

The main objective of this study is to investigate the effect of Cu–Cr and Cu–Mo powder metal (PM) tool electrodes on electrical discharge machining (EDM) performance outputs. The EDM performance measures used in the study are material removal rate (MRR), tool electrode wear rate (EWR), average workpiece surface roughness (R_a), machined workpiece surface hardness, abrasive wear resistance, corrosion resistance, and workpiece alloyed layer depth and composition. The EDM performance of Cu–Cr and Cu–Mo PM electrodes produced at three different mixing ratios (15, 25, and 35 wt% Cr or Mo), compacting pressures (P_c = 600, 700, and 800 MPa), and sintering temperatures (T_s = 800, 850, and 900 °C) are compared with those machined with electrolytic Cu and Cu PM electrodes when machining SAE 1040 steel workpiece. Analyses revealed that tool materials were deposited as a layer over the work surface yielding high surface hardness, strong abrasion, and corrosion resistance. Moreover, the mixing ratio, P_c, and T_s affect the MRR, EWR, and R_a values.     

Multi-response optimization of EDM with Al–Cu–Si–TiC P/M composite electrode

The present study investigates the relationship of process parameters in electro-discharge of CK45 steel with novel tool electrode material such as Al–Cu–Si–TiC composite produced using powder metallurgy (P/M) technique. The central composite second-order rotatable design had been utilized to plan the experiments, and response surface methodology (RSM) was employed for developing experimental models. Analysis on machining characteristics of electrical discharge machining (EDM) die sinking was made based on the developed models. In this study, titanium carbide percent (TiC%), peak current, dielectric flushing pressure, and pulse on-time are considered as input process parameters. The process performances such as material removal rate (MRR) and tool wear rate (TWR) were evaluated. Analysis of variance test had also been carried out to check the adequacy of the developed regression models. Al–Cu–Si–TiC P/M electrodes are found to be more sensitive to peak current and pulse on-time than conventional electrodes. The observed optimal process parameter settings based on composite desirability are TiC percent of 18%, peak current of 6 A, flushing pressure of 1.2 MPa, and pulse on-time of 182 μs for achieving maximum MRR and minimum TWR; finally, the results were experimentally verified. A good agreement is observed between the results based on the RSM model and the actual experimental observations. The error between experimental and predicted values at the optimal combination of parameter settings for MRR and TWR lie within 7.2% and 4.74%, respectively.     

Tribological Properties of a C/C–SiC–Cu Composite Brake Disc

A life-size composite brake disc was produced from Si, carbon–carbon composite, copper, and phenol resin. The disc had an outer radius Ø380, inner radius Ø180, and thickness of 36 mm. Chopped carbon fibers were used to reinforce frictional and structural layers. To obtain a preform of each layer, resin and carbon-fibers were mixed and hot-pressed. The preforms were pyrolyzed, and bonded by hot pressing. Finally Si and Cu infiltration in vacuum atmosphere was carried out to obtain a C/C–SiC–Cu _x Si _y composite brake disc. The density of the disc was 2.17 g/cm³. The bending strength was 61 MPa. The heat transfer coefficients in vertical and horizontal directions were 30.7, and 85.2 W/m-°C at 25°C, respectively. Friction coefficients of the C/C–SiC–Cu _x Si _y brake disc were more stable than those of C/C–SiC brake discs. X-ray diffraction analysis showed that Cu formed a compound, Cu₃Si.     

Microstructural evolvement and formation of selective laser melting W–Ni–Cu composite powder

W–Ni–Cu alloy (90 wt% W, 7.5 wt% Ni, and 2.5 wt% Cu) parts were successfully fabricated via selective laser melting method. Phases, microstructure, compositions, and laser forming parameters of laser melted samples were investigated. It was found that the W–Ni–Cu powder system was based on the mechanism of liquid solidification. This process was realized through full melting of W, Ni, and Cu particles under high laser energy input. However, using relatively lower energy input, particle bonding was realized through liquid phase sintering with complete melting of Ni–Cu acting as binder and nonmelting of W acting as structure. Due to the Ni–Cu solid solution phase that appeared in a wide range from 1,084 to 1,455 °C, a coherent matrix interface can be observed after solidification. The microhardness of laser-fabricated specimens varied with different powder layer thicknesses, resulting from the laser-treated condition and ability of trapped air in the loose powder bed to escape. The metallurgical mechanisms were also addressed.     

Influence of matrix hardness on honing engine cylinder liner with Cu–Sn–Fe–Ni diamond stones

In this work, three Cu–Sn–Fe–Ni matrices with different hardness were utilized in the diamond honing stones. Structures of the three matrices were investigated by X-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy, and the results showed that the Cu–Sn–Fe–Ni matrices were composed of the pure copper, pure iron and (Cu, Ni)₄₁Sn₁₁. The wear properties of the matrices were estimated by a pin-on-disk wear machine under dry conditions at room temperature in the air. The influences of hardness on the honing performances were studied in terms of the honed surface aspect, the honing efficiency and the throughput of cylinder liners. Among the three stones, the stone with matrix B (HRB 71) reaches the self-sharpening range in terms of the three aspects mentioned above. Compared this stone with a commercially available product, the former has better honing efficiency.     

Wear analysis of Cu–Al coating on Ti–6Al–4V substrate under fretting condition

Fretting behavior of Cu–Al coating on Ti–6Al–4V substrate was investigated with and without fatigue load. Soft and rough Cu–Al coating resulted in abrasive wear and a large amount of debris remained at the contact surface, which caused an increase in tangential force during the fretting test under gross slip condition. Fretting in the partial slip condition also showed the wear of coating. To characterize wear, dissipated energies during fretting were calculated from fretting loops and wear volumes were obtained from worn surface profiles. Energy approach of wear analysis showed a linear relationship between wear volume and accumulated dissipated energy. This relationship was independent of fatigue loading condition and extended from partial slip to gross slip regimes. As an alternate but simple approach for wear analysis, accumulated relative displacement range was correlated with the wear volume. This also resulted in a linear relationship as in the case of accumulated dissipated energy suggesting that the accumulated relative displacement range can be used as an alternative parameter for dissipated energy to characterize the wear. When the maximum wear depth was equal to the thickness of Cu–Al coating, harder Ti–6Al–4V substrate inhibited further increase in wear depth. Only when a considerable energy was supplied through a large value of the applied displacement, wear in the substrate material could occur beyond the thickness of coating.     

Effect of Micro-scale Y Addition on the Fracture Properties of Al–Cu–Mn Alloy

Rare earth (RE) elements have positive effects on Al alloy, while most research is focused on microstructure and mechanical properties. As important application indices, toughness and plasticity are properties that are sensitive to alloy fracture characteristics, and few research studies have characterized the fracture properties of Al–Cu–Mn alloy on RE elements. The effect of different contents of Y on the fracture properties of Al–Cu–Mn alloy is investigated. T6 heat treatment (solid solution and artificial aging treatment), optical microscope (OM), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) methods are applied to the alloy. Results showed that when Y element is present at 0.1%, the section of the as-cast alloy has smaller sized dimples and the fracture mode presents ductile features. Slight changes in hardness are also observed and maintained at about 60 HV. With increasing content of the RE element Y from 0.1 to 0.5%, the θ phase and Cu atoms in the matrix were reduced and most stopped at Grain boundaries (GBs). Micro-segregation and an enriched zone of Y near the GBs gradually increased. At the same time, the inter-metallic compound AlCuY is aggregated at grain junctions causing deterioration of the micro-structure and fracture properties of the alloy. After T6 treatment, the flatness of the fracture surface was lower than that of all the as-cast alloy showing lots of dimples and teared edges with a significant increase in hardness. When Y content was 0.1%, the strength and hardness of the alloy increased due to refinement of the grain strengthening effect. The content of Y elements segregated in the inter-dendritic zone and GBs is reduced. Plasticity and deformation compatibility also improved, making cracks difficult to form and merge with each other along adjacent grain junctions and providing an increased potential for ductile fracture. This paper proposes the addition of RE Y as an effective and prospective strategy to improve the fracture properties of the Al–Cu–Mn alloy and provide a meaningful reference in terms of improving overall performance.     

Thermo-mechanical treatments of Sc- and Mg-modified Al–Cu alloy welds

High-strength heat-treatable aluminum alloy AA2219 finds application in aerospace industries. Though it has good weldability, with alternating current–tungsten inert gas welding, the joint efficiency obtained is only 40%, particularly in thicker plates. In the present study, an attempt has been made to improve the weld metal properties by modifying the chemistry of fusion zone and post-weld thermo-mechanical treatments. Fillers were made through casting route by melting conventional 2319 filler with Sc and Mg. Two levels of Sc (0.3% and 0.6%) and four levels of Mg (0.3% to 0.6%) were varied. Compressive deformation was done on the fusion zone of the weld to get three levels of percentage of reduction (4%, 8%, and 12%). As welded specimens and welds after compressive deformation, those were subjected to post-weld aging treatments at 190ºC for different periods up to 100 h. Compressive deformation on the welds made with modified filler of 2319 with Sc and Mg resulted in significant improvement in the weld metal strength.     

Effects of Silicon Content on the Mechanical Properties and Lubricated Wear Behaviour of Al–40Zn–3Cu–(0–5)Si Alloys

In this work, one ternary Al–40Zn–3Cu and seven quaternary Al–40Zn–3Cu–(0.25–5)Si alloys were synthesized by permanent mould casting. Their microstructure, mechanical and lubricated wear properties were investigated using appropriate test apparatus and techniques. As the silicon content increased the hardness of the alloys increased, but their elongation to fracture decreased. Tensile strength of the alloys decreased with increasing silicon content following a sharp decrease and a slight increase. Among the silicon-containing quaternary alloys the highest and the lowest tensile strength values (348 and 305 MPa) were obtained with the Al–40Zn–3Cu–2Si and Al–40Zn–3Cu–5Si alloys, respectively, while the base alloy (Al–40Zn–3Cu) exhibited a tensile strength of 390 MPa. However, the volume loss due to wear of the alloys increased with increasing silicon content after showing an initial increase and a sharp decrease. The lowest wear loss was obtained with the alloy containing approximately 2% Si which has the highest tensile strength among the quaternary alloys containing more than 0.25% Si. Wear surfaces of the alloys were characterized mainly by smearing indicating that adhesion is the dominant wear mechanism for the experimental alloys.     

Formation of Laminar Structure Under Unlubricated Friction of Cu–SiO2 Composite

A laminar-structured tribolayer on the worn surface of Cu?CSiO₂ composite in sliding against 1045 steel is observed by etching the longitudinal sections. In morphology, the tribolayer consists of many subunits with different lengths and heights. The subunits are curved or parallel to the contact surface at different depths from bulk to the worn surface. In microstructure, the tribolayer is unconsolidated after etching, and fine Cu grains, as well as few fractured SiO₂ particles, are observed. The main formation mechanism of the laminar-structured tribolayer is grain boundary sliding. Shear localization with large plastic strain is a prerequisite for the formation of laminar structure. The generation and accumulation of frictional heating promote the plastic deformation and decrease the activation energy for grain boundary sliding. The etching effect is contributed to the presentation of the laminar structure.     

Selective laser melting W–10 wt.% Cu composite powders

Tungsten–Copper (W–Cu) alloys are promising materials for electrical and thermal applications. However, its forming method still remains limited in conventional powder metallurgy technique which is not suitable for manufacturing parts with intricate shapes. In this work, selective laser melting technology was introduced for fabricating W–10 wt.% Cu alloys parts. The morphological feature of a single molten track was analyzed. The results show that liquid phase sintering with complete melting of the binder (Cu), but nonmelting of the structural metal (W), acts as the main mechanism in this process. The melting conditions of single layers in different processing parameters were investigated. The results show that a moderate melting zone can be acquired from an established process map. Moreover, investigations on multilayers forming show that the final density increases with the decrease of scan speed until it reaches a plateau due to the insufficient rearrangement in liquid phase sintering and the balling effect.     

Dry Sliding Friction and Wear Properties of Al–25Zn–3Cu–(0–5)Si Alloys in the As-Cast and Heat-Treated Conditions

Dry sliding friction and wear properties of ternary Al–25Zn–3Cu and quaternary Al–25Zn–3Cu–(1–5)Si alloys were investigated using a pin-on-disc test machine after examining their microstructures and mechanical properties. An alloy (Al–25Zn–3Cu–3Si), which exhibited the highest tensile and compressive strengths, was subjected to T7 heat treatment. Surface and subsurface of the wear samples were investigated using scanning electron microscopy (SEM). The hardness and both tensile and compressive strengths of the alloys increased with increasing silicon content, but the trend reversed for the latter ones above 3% Si. It was observed that T7 heat treatment reduced the hardness and both tensile and compressive strengths of the Al–25Zn–3Cu–3Si alloy, but increased its elongation to fracture greatly. Three distinct regions were observed underneath the surface of the wear samples of the Al–25Zn–3Cu–3Si alloy. The formation of these regions was related to the heavy deformation of surface material and mixing, oxidation and smearing of wear material. Al–25Zn-based ternary and quaternary alloys in both as-cast and heat-treated conditions were found to be superior to SAE 660 bronze as far as their mechanical and dry sliding wear properties are concerned.     

Effects of speed sequence on friction properties of sintered Cu–SiO2

Abstract

The effects of the speed sequence and SiO₂ content of Cu–SiO₂, sintered by powder metallurgy method, on friction and wear properties have been investigated at fixed speeds. The results indicate that the sequence of speeds employed in the tests plays great roles in the friction and wear properties. When the tests are executed from a lower speed to a higher speed, friction coefficients decrease and oscillate dramatically as the speed goes up, resulting in a severe wear. On the contrary, as the speed starts from a higher value, the friction coefficients are stable and wear is small. These phenomena can be explained by states of third bodies formed in the friction. The third body formed at lower friction speeds is usually granular, which is responsible for the coefficient oscillations and larger wear loss. At higher speeds, the third body formed is rather dense, leading to stable friction coefficients and lower wear loss.     

Experimental and theoretical analysis of friction stir welding of Al–Cu joints

This paper presents a study of friction stir welding of aluminium and copper using experimental work and theoretical modelling. The 5083-H116 aluminium alloy and pure copper were successfully friction-stir-welded by offsetting the pin to the aluminium side and controlling the FSW parameters. A theoretical analysis is presented along with key findings. The process temperatures are predicted analytically using the inverse heat transfer method and correlated with experimental measurements. The temperature distribution in the immediate surroundings of the weld zone is investigated together with the microstructures and mechanical properties of the joint. This was supported by a finite element analysis using COMSOL Multiphysics. In this study, two rotational speeds were used and a range of offsets was applied to the pin. The microstructure analysis of the joints was undertaken. This revealed some particles of Cu inclusion in the nugget zone. The energy dispersive spectroscopy showed a higher diffusion rate of aluminium towards the interface while copper maintained a straight base line.     

TEM and electron holography analyses of granular and thin layered Cu–Co magnetic materials

The paper shows the examples of application of transmission electron microscopy (TEM) techniques for characterization of two types of copper–cobalt magnetic nanomaterials: Cu-10 wt% Co granular giant magnetoresistance (GMR) thin ribbons and thin nanocrystalline Co films deposited on Cu substrate. Quantitative TEM microstructural analyses were used for determination of Co particle size distributions in GMR ribbons. It was demonstrated that the relative resistivity depends on the mean diameter of the cobalt nanoparticles. For nanocrystalline thin Co layers, off-axis electron holography was used to investigate their magnetic structure. The mean in-plane component of the magnetic field in cobalt was calculated from the phase gradient.     

Pulse current auxiliary TLP diffusion bonding of SiCp/2024Al composite sheet using mixed Al–Cu–Ti powder interlayer

Pulse current auxiliary transient liquid-phase (TLP) diffusion bonding of SiCp/2024Al composite sheet was investigated at 580 °C using mixed Al–Cu–Ti powder interlayer. The optimal process parameters were applied as follows: pulse current density of 1.15?×?10² A/mm², pressure of 0.5 MPa, vacuum of 1.3 ×?10^?3 Pa, and bonding time from 15 to 60 min. The bonding quality is evaluated by microstructure characterization and mechanical properties of the joints. The mechanism of pulse current auxiliary TLP diffusion bonding process is analyzed. The results indicated that the dense joints without cavity consisted of the Al-based solid solution, pure Ti, Al₂Cu, and TiAl₃ intermetallic phase. Microhardness of joints was obviously higher than Cu diffusion zone and substrate materials zone. The shear strength of the joints monotonically increased with bonding time. The maximum value exceeded 154.1 MPa in bonding time of 60 min. Pulse current generated Joule heat, high-temperature spark plasma, and electromigration, which guarantee the feasibility of bonding process and high-quality joint.     

Wear behavior of Cu–La2O3 composite with or without electrical current

A new type Cu–La₂O₃ composite was fabricated by internal oxidation method using powder metallurgy. Sliding wear behavior of the Cu–La₂O₃ composites was studied by using a pin-on-disk wear tester under dry sliding conditions with or without electrical current, rubbing against GCr15 type bearing steel disk at a constant sliding speed of 20 m/s. The influence of varying applied load and electrical current was investigated. The worn surfaces were examined using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) to determine the wear mechanisms. The results showed the Cu–La₂O₃ composites had an electrical conductivity of 81.9% IACS (International Annealed Copper Standard, 100% IACS = 58 MS/m) and a hardness of HV105. The wear rate of the Cu–La₂O₃ composite pins increased with the increase in the electrical current at high sliding speed. The main wear mechanisms of the Cu–La₂O₃ composites were found to be adhesive wear, abrasive wear and arc erosion.     

The Microstructure and Wear Characteristics of Cu–Fe Matrix Friction Material with Addition of SiC

The Cu–Fe matrix continuous braking friction materials using SiC as abrasive were fabricated by powder metallurgy technique, and the effect of content and size of SiC were investigated. The tribological properties of friction materials sliding against AISI 1045 steel ring were carried out on a block-on-ring tester at different loads and sliding speeds. The strengthening effect of nano-SiC (55 nm) was superior to that of micro-SiC (70 μm) of the tribological properties for friction materials. The friction coefficients of friction materials increased with increasing nano-SiC content. However, the wear rates decreased with increasing nano-SiC content and then increased when the content of nano-SiC particle exceeded 10 wt%. The specimen contained 10% nano-SiC had the best tribological properties at different testing conditions.     

Characterisation of the early stages of solute clustering in 1Ni–1.3Mn welds containing Cu

Microstructural characterisation of neutron irradiated low alloy steels is important for developing mechanistic understanding of irradiation embrittlement. This work is focused on the early stages of irradiation-induced clustering in a low Cu (0.03 wt%), high Ni (∼1 wt%) weld. The weld was irradiated at a very high dose rate and then examined by atom probe (energy-compensated position-sensitive atom probe (ECOPoSAP) and local electrode atom probe (LEAP)) with supporting microstructural information obtained by small angle neutron scattering (SANS) and positron annihilation (PALA).