Experimental Investigations into the Effects of Microelectric-Discharge Milling Process Parameters on Processing Ti–6Al–4V

Microelectric-discharge milling is acquiring more importance in micromanufacturing because of its unique ability to produce three-dimensional microcavities with high aspect ratio in electrically conductive advanced materials regardless of its mechanical properties. The present study investigates the effects of major microelectric-discharge milling process variables [voltage (V), capacitance (C), electrode rotational speed (ERS), and feed rate (FR)] on Ti–6Al–4V. The output performance measures were identified as material removal rate (MRR) and tool wear rate (TWR) to assess the machinability of Ti–6Al–4V. Experiments were designed and carried out based on response surface methodology-Box-Behnken statistical design. The most influencing parameters for responses (MRR, TWR) were found to be capacitance and FR. At a capacitance of 0.4 µF and FR of 18 mm/min, maximum MRR of 0.9756 mg/h, and TWR of 0.6342 mg/h were observed. Similarly at 0.01 µF and 6 mm/min, minimum MRR of 0.2308 mg/h, and TWR of 0.1259 mg/h were obtained.     

Effect of Laser Parameters on Sintered Powder Morphology

Selective laser sintering is a kind of rapid prototyping process whereby a three-dimensional part is built layerwise by laser scanning a powder. This process is highly inffuenced by powder and laser parameters such as laser power, scan rate, spot size and layer thickness. Therefore a study on fabricating a line with Fe-Ni-Cr powder on AISI H13 tool steel has been performed by selective laser sintering. In this study, fabrication was performed by experimental facilities consisting of a 200W fiber laser which can be focused to 0.08 mm and atmospheric chamber which can control atmospheric pressure with argon. The line was fabricated with various laser power, scan rate and layer thickness. Line width and surface quality were investigated. With power increase or layer thickness decrease, line width was decreased and line surface quality was improved with scan rate optimization.     

Deposition and Analysis of Composite Coating on Aluminum Using Ti–B4C Powder Metallurgy Tools in EDM

The present work investigates the method of depositing a ceramic coating on the surface of aluminum by means of electrical discharge coating (EDC) in electrical discharge machining (EDM). The present study makes use of powder metallurgy (P/M) green compacts made of titanium, boron carbide, and aluminum (Ti + B₄C + Al) powder as the EDM tool for surface modification of aluminum workpieces. EDM process was carried out with different tool parameters like composition of the electrode material, compaction pressure of the green compacts, and different settings of the process variables like peak current and pulse duration setting. Responses observed were material deposition rate (MDR), tool wear rate (TWR), and average layer thickness (LT). Experiments were designed and carried out using Taguchi L₁₈ orthogonal array. The most influential parameter for responses MDR, TWR, and LT was found to be peak current (I_p) with a percentage contribution of 60.72%, 59.52%, and 42.09%, respectively. In addition, various other characterization techniques such as optical microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectrum (EDX) analysis were performed in order to judge different attributes of the deposited coating.     

Effect of Homogenization Process on Microstructure of Al–Zn–Mg–Cu Aluminum Alloys

Herein, the best homogenization process of 466.5 °C × 36 h + 490 °C × (14–26.4 h) that can completely eliminate the coarse phases σ[Mg(Zn, Al, Cu)₂] and S(Al₂CuMg) in the Al–Zn–Mg–Cu aluminum alloy is developed. The homogenization process is determined by the method of calculation phase diagram, and the experimental verification. It is shown in the results that, first, in the microstructure of the as-cast alloys, the crystal structure of the σ[Mg(Zn, Al, Cu)₂], Al₇Cu₂Fe, and Mg₂Si phases is determined. Second, during the homogenization process, the σ[Mg(Zn, Al, Cu)₂] phase dissolves and also transforms into the S(Al₂CuMg) phase. Most importantly, the dissolution temperature range of the σ[Mg(Zn, Al, Cu)₂], S(Al₂CuMg), and Al₇Cu₂Fe phases is determined from 472.56 to 476.36 °C, from 484.09 to 485.39 °C, and from 540.18 to 547.23 °C, respectively. At best homogenization process, the residual Al₇Cu₂Fe phase area fraction ranges from 1.28 ± 0.16% to 1.60 ± 0.18%. In addition, dispersed η(MgZn₂) phase precipitates in supersaturated Al-matrix during differential scanning calorimeter heating. And, the concentration differences between the grain center and the eutectic of structure of Zn, Mg and Cu regression equations are established, which can provide some reference for the design of experimental parameters, thus reducing the experimental workload.     

Influence of Process Parameters on Cu–Fly Ash Composite by Powder Metallurgy Technique

In this study influence of compaction pressure, sintering temperature, and sintering time on mechanical and wear behavior of the fly ash reinforced copper-based composites are analyzed. The composites were prepared by powder metallurgy (P/M) technique with copper as matrix, 5 and 10 wt% of fly ash as reinforcement. The green compacts were prepared at three different pressures such as 350, 400, and 450 MPa. The prepared green composites were sintered at 700, 800, and 900 °C for the time period of 30, 60, and 90 min, respectively. From the results it is observed that when the process parameter increases the density, hardness, compression strength, and wear resistance increases.     

Influence of TiC particle size on the load-independent hardness of Al2O3–TiC composites

Seven samples of Al₂O₃–30 wt.% TiC composites were prepared by hot-pressing the Al₂O₃ powder mixed with TiC particles of different particle sizes. Knoop and Vickers hardness measurements were conducted on these samples, respectively, in the indentation load range from 1.47 to 35.77 N. The load-independent hardness numbers were then determined by analyzing the relationship between the measured indentation size and the applied indentation load. It was found that the load-independent hardness number increases with the increasing TiC particle size, and this experimental phenomenon may be attributed to the effect of the residual internal stress resulting from the mismatch between the thermal expansion of Al₂O₃ matrix and that of the TiC particles.     

Flux-assisted spreading of an Al–7 wt%Si alloy on TiC

The effect of a K–Al–F-based flux was investigated on the wettability of TiC by an Al–7 wt%Si alloy in the interval of temperatures between 660 and 900 °C in Ar and in atmospheric air. Null spreading was observed without flux whereas perfect wetting was enabled by the flux in both atmospheres. The liquid flux, which provides a locally protective atmosphere by spreading on the surfaces of the substrate and eventually on the Al alloy, dissolves the aluminium oxide covering the molten alloy enabling thus direct contact between the liquid alloy and the TiC substrate. The low tensions for the solid/flux and liquid metal/flux interfaces facilitate spontaneous spreading and instantaneous wetting. Meanwhile, the flux is displaced to the lateral periphery of the substrate and to the surface of the liquid. Under the resolution of the scanning electron microscope, microstructural examination of the interfaces did not reveal reaction products. Rapid infiltration of the alloy into TiC/flux compacts, at low temperatures, correlated well with the flux-assisted spreading kinetics observed.     

Sintered porous cermets based on TiB2 and TiB2–TiC–Mo2C

TiB₂ powder, with different binders (Ni and Ni/Mn), after milling were cold compacted (300 MPa) and sintered in H₂ at 1300 and 1350°C for 1 h. To improve the sintering behaviour, TiC/Mo₂C alloy carbide was added and the milled charge along with the same binders (Ni and Ni/Mn) was cold compacted and sintered under similar conditions. Sintered density, porosity, transverse rupture strength (TRS), grain size and lattice parameter of binder and hard phases were measured. Better densification was observed with Ni/Mn binder as compared to Ni binder for either hard phase based systems. Maximum value of TRS was noted for TiB₂–TiC–Mo₂C–40 wt.% Ni/Mn cermet. Melt exudation was observed for either hard phase based systems with Ni binder.     

Influence of Experimental Parameters on Reactive Magnetron Sputtering CN_x Thin Films

Carbon nitride thin films were deposited on Si(001) using unbalanced magnetron sputtering at different experimental parameters. The effects of nitrogen partial pressure, substrate temperature and substrate bias on the deposition rate and nitrogen content are discussed.     

Nanocrystalline matrix TiC–Al3Ti and TiC–Al3Ti–Al composites produced by reactive hot-pressing of milled powders

Mechanically alloyed nanocrystalline TiC powder was short-term milled with 40 vol.% of Al powder. The powders mixture was consolidated at 1200 °C under the pressure of 4.8 GPa for 15 s and at 1000 °C under the pressure of 7.7 GPa for 180 s. The bulk materials were characterised by X-ray diffraction, light and scanning electron microscopy, energy dispersive spectroscopy, hardness, density and open porosity measurements. During the consolidation a reaction between TiC and Al occurred, yielding an Al₃Ti intermetallic. The microstructure of the produced composites consists of TiC areas surrounded by lamellae-like regions of Al₃Ti intermetallic (after consolidation at 1200 °C) or Al₃Ti and Al (after consolidation at 1000 °C). The mean crystallite size of TiC is 38 nm. The hardness of the TiC–Al₃Ti and TiC–Al₃Ti–Al composites is 13.28 GPa (1354 HV1) and 10.22 GPa (1041 HV1) respectively. The produced composites possess relatively high hardness and low density. The results obtained confirmed satisfactory quality of the consolidation with keeping a nanocrystalline structure of TiC.     

Study on the machining of Al–SiC functionally graded metal matrix composite using die-sinking EDM

Functionally graded aluminum matrix composites (FGAMCs) are new materials with excellent capabilities for design and development of complex engineering works. In this work, FGAMCs are machined using electrical discharge machining (EDM) with the process input parameters such as pulse current, pulse on time, and zone position in brake disk. Design of experiments is used for the experimental planning with full factorial method. The selected input process parameters are optimized using gray relational analysis to minimize the electrode wear ratio, overcut, power consumption, and surface roughness. The influential studies of input process parameters on the output responses are also conducted. The optimal EDM parameter setting for achieving better output parameters is pulse current at 5 A, pulse on time at 50?µs and 45?mm zone position distance in the brake disk. The pulse current (39.40%) contributed the maximum in minimizing the output responses. Further, the surface morphology is also analyzed on the material to observe the crater formation and the erosion mechanism.     

Production of Fe3Al–TiC nanocomposite by mechanical alloying of FeTi2–Al–C powders

Abstract

The aim of the present work was to produce Fe₃Al/TiC nanocomposite by mechanical alloying of the FeTi₂30Al10C60 (in at-%) powder mixture. The morphology and the phase transformations in the powder during milling were examined as a function of milling time. The phase constituents of the product were evaluated by X-ray diffraction (XRD). The morphological evolution during mechanical alloying was analysed using scanning electron microscopy (SEM). The results obtained show that high energy ball milling, as performed in the present work, leads to the formation of a bcc phase identified as Fe(Al) solid solution and an fcc phase identified as TiC and that both phases are nanocrystalline. Subsequently, the milled powders were sintered at 873 K. The XRD investigations of the powders revealed that after sintering, the material remained nanocrystalline and that there were no phase changes, except for the ordering of Fe(Al), i.e. formation of Fe₃Al intermetallic compound, during the sintering process.     

Effect of Cryogenic Cooling of Tool Electrode on Machining Titanium Alloy (Ti–6Al–4V) during EDM

The discharge characteristics and discharge gap of machining Ti–6Al–4V titanium alloy by cryogenically cooled tool electrode electrical discharge machining (EDM) in distilled water were investigated in this study using the monopulse discharge method. The influence of the cryogenically cooled tool electrode on the discharge gap and the initial maintaining voltage between the electrode and workpiece were analyzed under various temperatures. Test results showed the initial maintaining voltage of the cryogenically cooled tool electrode EDM was lower than that of conventional EDM. The discharge gap of the cryogenically cooled tool electrode EDM was also smaller than that of conventional EDM, which improved the copying accuracy of die-sinking EDM. A comparative experiment of machining Ti–6Al–4V titanium alloy was carried out by using cryogenically cooled tool electrode EDM and conventional EDM, lower electrode wear, higher material removal ratio, and higher corner size machining accuracy was obtained by using cryogenically cooled tool electrode EDM.     

Analysis of cellular microstructures in Al–Fe–Si alloy

Abstract

Experiments have been carried out on a commercial aluminium alloy rolled to foils with various high rolling reductions. Attention was focused on the formation of cells during deformation. Microstructures were examined in the SEM using electron backscatter diffraction (EBSD) and oriented imaging microscopy techniques. A treatment of the results obtained with EBSD has been used to determine the discrete parameters of the individual grains in the aggregate. The local driving pressures were calculated enabling the estimation of grain growth velocities dR/dt. The evolution of texture could be predicted and successfully compared with the experimental results of an annealing treatment.     

Characteristics of TiC dendrites in as solidified Ti–Al–C alloys

Abstract

Results are reported on the dendrite secondary arm spacing of a series of as cast Ti–C and Ti–Al–C alloys in the composition range up to 10 at.-%C and 15 at.-%Al. The presence of Al leads to a significant decrease in the dendrite spacing, an effect of potential interest for improving mechanical properties. The structural refinement is attributed mainly to the slower diffusion of Al as compared with carbon, in the solute partitioning required for coarsening of dendrite arms.     

Characterization of Mo–Si–B Nanocomposite Powders Produced Using Mechanical Alloying and Powder Heat Treatment

Mo–Si–B nanocomposite powders with a composition of Mo–12Si–8.5B(in at.%) were processed using mechanical alloying under milling conditions for different milling time and powder-to-ball ratios. The Mo–12Si–8.5B alloy, which consists of α-Mo and intermetallic Mo3 Si and T2 phases, was also synthesized by hot-pressed sintering the mechanically alloyed powders under a pressure of 50 MPa at 1600 °C.The results demonstrated that the sizes and morphologies of the powder particles became gradually refined and uniform by both increasing the milling time and decreasing the powder-to-ball ratio. After 15 h of milling, the powders were completely homogenized at the 1:10 and the 1:15 powder-to-ball weight ratios,and the homogenization was accelerated to rapidly stabilize the milling process because of their high milling energy. Annealing the Mo–Si–B milled powders could promote the growth of the intermetallic Mo3 Si and the T2 phases, which formed even after low-temperature annealing at 900 °C. Increasing the annealing temperature only improved the crystallinity of various phases. When the milled and annealed powders were hot-pressed sintered, the Mo–Si–B alloy exhibited a fine-grained microstructure,where the intermetallics Mo3 Si and T2 were distributed in a continuous α-Mo matrix.     

Optimization of EDM Parameters on Machining Si3N4–TiN Composite for Improving Circularity,Cylindricity, and Perpendicularity

The dominance of the spark eroding process in complex ceramic components has promoted a significant growth analysis in the ceramic composites domain in modern manufacturing industries. The latest developments in ceramic components are concentrated on both the enhancement of the mechanical properties and the machinability of complex 3D parts while using spark EDM. The current (I), pulse on time (T_on), pulse off time (T_off), and dielectric flushing pressure (DP) are considered sparking parameters for the machining of a Si₃N₄–TiN ceramic composite. These composites find their application in high-temperature environments, viz. metal forming, extrusion dies, turbine blade, and non-ferrous molten metal handling components. Taguchi's orthogonal array (OA), L₁₈, has been used to design the experiments. The optimal machining inputs are determined by the grey relational grade (GRG), which is attained from the grey relation analysis (GRA) for various response characteristics, such as the material removal rate (MRR), tool wear rate (TWR), circularity (CIR), cylindricity (CYL), and perpendicularity (PER). The significant parameters are identified via an analysis of variance (ANOVA). Finally, the optimized process parameters resulting in a higher MRR, lower TWR, lower form tolerance, and decreased orientation tolerance are verified through a confirmation test demonstrating that sparking process responses can be effectively improved.