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The near-dry electrical discharge machining processes have been conducted using air-mist or gas mist as a dielectric fluid to minimize the environmental impacts. In this article, near-dry electrical discharge machining (NDEDM) experiments have been performed to improve machining performance using an oxygen-mist dielectric fluid, a copper composite electrode, and Cu-Al-Be polycrystalline shape memory alloy (SMA) work materials. The copper composite electrode is made up of 12 wt% silicon carbide and 9 wt% graphite particles. The oxygen-mist pressure (Op), pulse on time (Ton), spark current (Ip), gap voltage (Gv), and flow rate of mixed water (Fr) were used as process parameters, and the material removal rate (MRR), tool wear rate (TWR), and surface roughness (SR) were used as performance characteristics. The global optimal alternative solution has been predicted by the PROMETHEE-II (Preference Ranking Organization METhod for Enrichment Evaluations-II) optimization technique. The best combinations of process parameters have been used to examine the microstructure of composite tools and SMA-machined surfaces by scanning electron microscopy (SEM) analysis. The best global optimum settings (oP: 9 bar, Ip: 60 µs, Ip: 12 A, Gv: 40 V, and Fr: 12 ml/min) are predicted to attain optimum machining performance (MRR: 39.049 g/min, TWR: 1.586 g/min, and SR: 1.78 µm). The tool wear rate of the NDEDM process has been significantly reduced by the copper composite electrode due to increasing microhardness, wear resistance, and melting point. When compared to the pure copper electrode tool, the MRR of NDEDM is improved to 21.91%, while the TWR and SR are reduced to 46.66% and 35.02%, respectively. [ABSTRACT FROM AUTHOR]

Metal matrix composites have significant applications in the engineering field. During service, the fracture is one of the most typical failure modes. In this study, the digital image-based technique (DIT) combined with a micro-scale damage cohesive finite element model (CFEM) was employed to reconstruct the microstructures of metal matrix composites with the arbitrary morphology of particles. The cohesive finite element in this model can predict the process of crack initiation and propagation spontaneously, and the effectiveness of the model was verified by the in-situ tensile tests of the compacted graphite iron (CGI) sample. We found that the morphology and distribution of the graphite particles play important roles in crack initiation and propagation under tensile and compressive loadings. The relationship between the graphite particle size and yield strength was established, and an optimal graphite particle size was found for the maximum yield strength, which is different from the previous results. The relationship between microstructures and tensile properties of CGI could contribute to the design and development of metal matrix composites with optimal mechanical properties.

Cast iron is an important engineering material, used extensively in industrial applications. Despite being often exposed to complex thermomechanical loading, its performance under such conditions is not fully identified because of its complex microstructure. In this work, a response of cast iron to pure thermal loading is studied employing a micromechanical approach. Specifically, 2D representative volume elements (RVEs) are generated employing material characterisation data and analysed using a finite-element approach. These RVEs comprise a ferritic matrix enveloping a single graphite particle, represented as an ellipse. The developed numerical strategy allows a parametric analysis of the effects of graphite morphology and boundary conditions applied. In addition, a model with a graphite particle modelled as a void is investigated to study the accuracy of the obtained results for the thermal load. The obtained results are expected to be useful in the future design of this engineering alloy. [ABSTRACT FROM AUTHOR]

To obtain multimaterial structures composed by various materials as the right man in the right place for improvement of the additional value of some products or parts, the easy manufacturing method of the dissimilar metal joint is necessary. This paper described the weldability and its improvement of the friction welded joint between ductile cast iron (JIS FCD400) and typical Al-Mg alloy (JIS A5052). When both materials welded, only the A5052 side was unilaterally deformed and that was exhausted as flash during the friction process regardless of the friction welding condition. The relatively high tensile strength of the joint was obtained when that was made with a friction speed of 27.5 s−1, a friction pressure of 20 MPa, a friction time of 1.5 s, and a forge pressure of 270 MPa. However, the joint had approximately 77% in the tensile strength of the A5052 base metal and that was fractured at the weld interface. The tensile strength of joints, which were made with other friction welding conditions, was lower than that of this friction welding condition. Although the weld interface of the joint had no intermetallic compound interlayer, the fractured surface at the A5052 side had the C element as the graphite particles that were supplied from the FCD400 side. To improve the joint strength, the graphite particle was reduced from the weld faying surface at the FCD400 side by decarburization treatment before welding. The joints had approximately 97% in the tensile strength of the A5052 base metal, and one of joints was fractured at the A5052 base metal. Thus, the graphite particle at the FCD400 side influenced the weldability between FCD400 and A5052. In conclusion, the joint with high tensile strength as well as the possibility for the improvement of the fractured point of them could be obtained when they were made with an opportune friction welding condition and no graphite particles at the weld faying surface of the FCD400 side.

[Display omitted] • The adhesion of particles on rough wall was measured by AFM. • FEM coupled with Lennard-Jones potential is used to simulate the influence factors of adhesion. • Simulation results were compared with JKR model and AFM measurements. • The roughness of wall was a key factor to determine adhesion. The characteristics of how graphite particles adhere to the walls of high-temperature gas-cooled reactors are very important for analyzing reactor source terms. In the present study, atomic force microscopy (AFM) is used to measure the particle adhesion force and the wall morphology, then Lennard-Jones potential theory and the finite element method (FEM) are coupled to calculate the adhesion force between different particles and rough walls. The obvious deviations between the AFM measurements and the theoretical models are due to the contact hypothesis of a sphere with a smooth flat plane in the latter. The FEM results reveal the formation of maximum adhesion at the pull-off point of the particle and the corresponding stress distribution. For aspherical particles, the local curvature of the particle contact interface is the main factor affecting the adhesion force. In addition, for rough walls, different contact regimes correspond to different adhesion trends. When discrete wall roughness with hemispheres and truncated cones is used, the FEM predictions are closer to the AFM measurements, indicating that roughness dominates the adhesion weakening. [ABSTRACT FROM AUTHOR]

The thermal conductivity of a magnetic fluid is expected to enhance by adding micron-sized particles with high thermal conductivity. The thermal conductivity of the magnetic fluid containing micron-sized graphite particles was investigated experimentally. The shapes of the graphite particles were sphere and flake-like. As the results of visualization experiments using the dark field microscope, the spherical graphite particles form chain-like clusters under applied magnetic field, while the fibrous structure is formed by the flake-like graphite particles, however, chain-like cluster formation cannot be clearly observed. The experiments using the transient hot-wire method showed that the thermal conductivity of magnetic fluid containing graphite particles is enhanced by applying magnetic field and by increasing the volume fraction of graphite particles. [ABSTRACT FROM AUTHOR]

In order to improve the recovery of iron resource in molten basic oxygen furnace (BOF) slag through carbothermal reduction, bottom blowing argon gas is used to promote the mixing efficiency between molten slag and graphite particles in the converter. In the present work, computational fluid dynamic-discrete particle model (CFD-DPM) method coupled with the reduction kinetic model of FeO in molten slag by graphite particle is employed to simulate the multiphase system composed of molten slag, graphite particle and argon gas. The motion and dispersion characteristics of graphite particles in a bottom-blown converter were mainly investigated, and the decrease of graphite particle diameter caused by the reduction reaction was considered. A particle dispersion index was also proposed to evaluate the distribution uniformity of graphite particles in the molten slag. In addition, the effects of initial particle diameter and bottom tuyere arrangement on the dispersion characteristics of graphite particles were further discussed. The results show that the proportion of large-sized particles is higher in the inactive-flow zone and the motion trajectory of graphite particles can be divided into two regimes. Graphite particles with an initial diameter of 5 mm and the converter with six bottom-blown tuyeres are more conducive to the homo-dispersion of graphite particles. The dispersion characteristics of graphite particles in a bottom-blown converter were investigated for molten BOF slag reduction. Based on the migration distance and particle size decrease, the motion trajectory of graphite particles can be divided into two regimes. Graphite particles with an initial diameter of 5 mm and the converter with six bottom tuyeres are more conducive to the particle homo-dispersion and reduction of molten BOF slag. [Display omitted] • Reduction reaction-induced decrease in graphite particle diameter is studied. • The motion trajectory of graphite particles can be divided into two regimes. • A dispersion index is proposed to assess graphite particle distribution uniformity. • 5 mm particle diameter and 6 tuyeres are conducive to the particle homo-dispersion. [ABSTRACT FROM AUTHOR]

Previous studies on the safety of gas-cooled high-temperature reactors (HTR) have analyzed the corrosion and oxidation behavior of the primary circuit components under normal and accident conditions. Through the use of graphite components, graphite particles can be formed by mechanical and chemical means whose influence on the structural change of metal surfaces must be analyzed in a comprehensive manner. The dust resuspension and deposition in tank geometry (DRESDEN-TANK) test facility was set up to thermally anneal metallic samples (Alloy 800H, Inconel 617) loaded with graphite particles under typical HTR conditions (helium, 750 °C, 6 MPa) for the investigation of interactions over a long-term range. In addition to the carrying out of a description of the processes occurring on the material surface, the gaseous reaction products have been analyzed. The results show that the presence of graphite particles in the near-surface layer has a significant impact on corrosion processes due to thermally-induced interactions. In this case iron and chromium are degraded in the metallic alloys, which leads to a structural change in the near-surface layer. Furthermore, the graphite particles significantly influence the formation of the oxide layers on the alloys; for example, they influence the formation speed of the layer and the layer height. The originally deposited particles thus exhibit a chemically-altered composition and a different geometric shape.

Experimental investigations of the characteristic stages of the processes of heating, evaporation, and explosive disintegration of inhomogeneous water droplets (with a commensurate graphite inclusion) in a high-temperature (600-1200 K) gaseous medium are carried out. Three methods of heating droplets differing in the dominating mechanism of heat transfer are used: heating in a muffle tube furnace (thermal radiation), in a stream of heated air (radiative-convective heat transfer), and in a stream of high-temperature combustion products of a typical liquid fuel (radiative-convective heat transfer). Characteristic values of each heat flux component ate determined for the conditions of experiments, as well as their dependences on temperature. It is shown that the highest values of the radiative heat flux (determining one from the viewpoint of the origination of the effect of explosive fragmentation of droplets) correspond to the schemes of heating in a stream of combustion products and in a tubular muffle furnace. The threshold values of the gaseous media temperatures at which a stable explosive disintegration of evaporating inhomogeneous droplets is realized (Tg > 850 K for conditions of heating in a stream of heated air, Tg > 800 K for the tubular muffle furnace, and Tg > 600 K for a stream of combustion products) have been obtained experimentally. With the use of thermocouple measurements the assumption on accumulation of the energy of thermal radiation near the liquid-solid particle interface and on the resulting formation of an additional source of liquid fi lm heating has been confirmed, which leads to the overheating of the liquid and to explosive disintegration of the droplet. [ABSTRACT FROM AUTHOR]

The present article investigates the effect of graphite particles on the wear behaviour of particle-reinforced hybrid aluminium matrix composites, based on Taguchi's L27 orthogonal array. Dry sliding wear tests were conducted using a pin-on-disc wear tester. Empirical relationship is established with major factors to estimate the wear using regression analysis. The results indicate that the developed model is suitable for prediction of wear on hybrid composite. The influence of different parameters such as load, rotational speed and percentage of graphite on wear of Al6063/Al2O3p/Grp composites has been analyzed through ANOVA table and contour graphs. The results revealed that addition of graphite particles reduces the wear of the hybrid composite under all conditions. [ABSTRACT FROM AUTHOR]

Discarded florescent tubes and graphite rods obtained from dumped primary cells have been processed to obtain glass and graphite particles. 80 µm glass and graphite particles were used as reinforcements in epoxy resin, LY 556 cured with HY 931 hardener to produce epoxy resin hybrid composites. The morphology, mechanical properties, thermal stability and wear resistance characteristics of the epoxy resin glass/graphite hybrid composites were studied. The thermogravimetric analyser TGA 701 was used to examine the thermal stability of the epoxy resin glass particle/graphite composites. Addition of graphite and glass particles enhanced the strength, thermal stability and wear resistance of the epoxy resin. However, tensile strain and impact energy absorption of the epoxy resin hybrid composites started declining at 6 wt% of glass particle addition. The increase in wear rate of the composites with an increment in applied loads is attributable to increase in the normal reaction between the examined sample surfaces and the emery paper. Furthermore, the increase in wear resistance with an increment in wt% of glass particle additions is attributable to good interfacial adhesion between matrix and the fillers. The textural and appearance differences between the scanning electron micrographs of the control and epoxy resin hybrid composites is attributable to the presence of new phases due to exothermic and cross linking reaction between the matrix and the fillers. Hence, new vital engineering composites peculiar to automobile, aerospace and building industries have been produced. [ABSTRACT FROM AUTHOR]