Evaluation of the Surface Integrity and Recast Layer in Electrical Discharge Turning of WC-Co Composites.

Tungsten carbide (WC) and its composites are typically associated with high hardness and high wear resistance, posing challenges in conventional machining processes like turning. To address the machining difficulties of WC-Co, electrical discharge turning (EDT) was proposed. The rotational speed in EDT is a key factor influencing the machining results; however, conflicting reports exist about its impact on the EDT process. Therefore, the effect of rotational speed on three different machining regimes, including roughing, semi-finishing, and finishing, was investigated using energy-dispersive X-ray spectroscopy (EDX), SEM, and roughness tests. Additionally, elemental mapping was applied to illustrate the element distribution on the machined surface. The results indicated that increasing the rotational speed led to a 10% to 17% decrease in the recast layer thickness and a 14% to 54% reduction in the surface roughness (Ra).

Experimental Study on the Comparison between Network Microstructure Titanium Matrix Composites and Ti6Al4V on EDM Milling.

Network microstructure titanium matrix composites (NMTMCs), featuring Ti6Al4V as the matrix and network-distributed TiB whiskers (TiBw) as reinforcement, exhibit remarkable potential for diverse applications due to their superior physical properties. Due to the difficulty in machining titanium matrix composites, electrical discharge machining (EDM) stands as one of the preferred machining techniques for NMTMCs. Nevertheless, the compromised surface quality and the recast layer significantly impact the performance of the workpiece machined by EDM. Therefore, for the purpose of enhancing the surface quality and restraining the defects of NMTMCs, this study conducted comparative EDM milling experiments between NMTMCs and Ti6Al4V to analyze the effects of discharge capacitance, charging current, and pulse interval on the surface roughness, recast layer thickness, recast layer uniformity, and surface microcrack density of both materials. The results indicated that machining energy significantly influences workpiece surface quality. Furthermore, comparative experiments exploring the influence of network reinforcement on EDM milling revealed that NMTMCs have a higher melting point, leading to an accumulation phenomenon in low-energy machining where the reinforcement could not be completely removed. The residual reinforcement in the recasting layer had an adsorption effect on molten metal affecting the thermal conductivity and uniformity within the recasting layer. Finally, specific guidelines are put forward for optimizing the material's surface roughness, recast layer thickness, and uniformity, along with minimizing microcrack density, which attain a processing effect that features a roughness of Ra 0.9 µm, an average recast layer thickness of 6 µm with a range of 8 µm, and a surface microcrack density of 0.08 µm-1.

Study on Forming Mechanism of the Recast Layer on the Workpiece Surface during Micro EDM.

In comparison to conventional EDM, micro EDM distinguishes itself through its brief discharge duration, narrow discharge channel radius, and concentrated energy density. However, there remains a paucity of comprehensive research on the surface formation characteristics in this domain. This paper delves into the formation mechanism of the recast layer in micro EDM workpieces, scrutinizing the primary factors that influence the formation process and the morphological attributes of the recast layer. We conducted a series of single-pulse experiments and micro EDM trials. Utilizing surface fitting tools, our experimental findings facilitated the derivation of a relational expression between the recast layer thickness of high-speed steel and the discharge parameters in micro EDM. Notably, when the energy is below 100 µJ, the recast layer thickness remains under 10 µm. Specifically, at an energy level of 16 µJ, opting for a smaller capacitance of 2200 pf and a higher voltage of 120 V in micro EDM results in a thinner recast layer. This study serves as a cornerstone for future efforts aimed at controlling and assessing the surface morphology of micro EDM.

Critical pulse in multi-shot femtosecond laser ablation on metallic surfaces.

Thermal effect remains a thorny issue for femtosecond-laser surface engineering and nanostructuring on metallic targets with high pulse energies or high repetition rates, which needs to be paid adequate attentions. Herein, we have experimentally investigated the heat diffusion and accumulations during single-shot and multi-shot femtosecond laser ablation on metallic surfaces. We have for the first time observed a novel phenomenon that the thermal effect was intensified abruptly when the laser-pulse number goes over a threshold (approximately between 10 and 20 for aluminum alloy with laser fluence of 6 J cm-2), accompanied with a dramatic reduction of ablated depth and complicated plasma dynamics. Based on both optical and thermodynamic analysis, we introduced a defocusing-dominated plasma-assistant model for this abnormal thermal effect. This work explored the critical experimental parameters for femtosecond-laser surface modification and processing in micro-scale engineering applications.

Experimental Study of the Surface Quality of Form-Cutting Tools Manufactured via Wire Electrical Discharge Machining Using Different Process Parameters.

Form-cutting tools are an economical choice for turning parts with defined profiles in mass production. The effects of the form contour of these tools-produced by the wire electrical discharge machining (WEDM) process-on tool quality were investigated in this research. This study focuses on reducing the adverse effects of the recast layer induced by WEDM on form-cutting tools. The basic component types of profile forms in form-cutting tools can be summarized by a combination of four modes, i.e., concave and convex arcs and flat and oblique surfaces. Hence, sample cutting tools with three different radii of convex and concave arcs and a flat surface were produced. During the WEDM operation, one-pass mode was used for roughing, two passes for semi-finishing, and three passes for finishing. Furthermore, the difference between the percentage of oxygen and carbon elements on the recast layer in the two areas above the workpiece or wire entry point and the bottom area of the workpiece or wire exit point was investigated. Finally, the influences of the direction, size of the curvature, and the number of passes in the wire electric discharge process on the recast layer were analyzed. It was observed that the recast layer thickness could be reduced by increasing the number of WEDM process. Additionally, the uniformity of the cutting contour was superior in the entry region of the wire going into the workpiece compared with the exit region of the wire.

Limitations of reuse for silver-palladium alloys -Evaluating post-recasting heat treatment impact on corrosion resistance.

The aim of this study was to investigate the effect of repeated casting and heat treatment on the corrosion resistance of a commercial Ag-Pd-Cu-Au alloy as evaluated by electrochemical techniques. After repeated casting, the fifth cast of the Ag-Pd-Cu-Au alloy exhibited dramatic degradation of properties, although upon heat treatment, this corrosion resistance did improve. Despite the improvement by heat treatment, after five castings, this alloy may not have satisfactory hardness for clinical use. These results of this study demonstrate that, up to the fourth cast and heat treatment, the Ag-Pd-Cu-Au alloy has acceptable corrosion resistance and hardness.

Investigation of Plasma-Electrolytic Processing on EDMed Austenitic Steels.

This study investigates the effect of electrolytic plasma processing on the degree of defective layer removal from a damaged layer obtained after manufacturing operations. Electrical discharge machining (EDM) is widely accepted in modern industries for product development. However, these products may have undesirable surface defects that may require secondary operations. This work aims to study the die-sinking EDM of steel components followed by the application of plasma electrolytic polishing (PeP) to enhance the surface properties. The results showed that the decrease in the roughness of the EDMed part after PeP was 80.97%. The combined process of EDM and subsequent PeP makes it possible to obtain the desired surface finish and mechanical properties. In the case of finishing EDM processing and turning, followed by PeP processing, the fatigue life is enhanced without failure up to 109 cycles. However, the application of this combined method (EDM + PeP) requires further research to ensure consistent removal of the unwanted defective layer.

Formation and Characterization of the Recast Layer Formed on Inconel 718 during Wire Electro Discharge Machining.

The present work investigates the formation and microstructural and micro-mechanical characterization of the recast layer that formed on Inconel 718 alloy in the course of the wire electro-discharge machining (WEDM). The as-machined surface contains globules, shallow cracks, and re-deposition of molten materials, together with the elements from the decomposition of wire electrode and electrolyte, which does not exceed beyond the surface of the recast layer. Under presently investigated machining parameters, the recast layer was about 6.2 ± 2.1 µm thick. There was no presence of a heat-affected zone (HAZ), as otherwise indicated for other hard-to-cut materials. The transmission electron microscopy (TEM) and electron back-scattered diffraction (EBSD) investigations show that the microstructure of the recast layer is similar to that of bulk alloy. Micro-mechanical characterizations of the recast layer were investigated via in-situ micro-pillar compression on the micro-pillars fabricated on the recast layer. The strength of the superficial layer (1151.6 ± 51.1 MPa) was about 2.2 times higher than that of the base material (523.2 ± 22.1 MPa), as revealed by the in-situ micro-pillar compression.

On the WEDM of WNbMoTaZrx (x = 0.5, 1) Refractory High Entropy Alloys.

As a potential candidate for the next generation of high-temperature alloys, refractory high entropy alloys (RHEAs) have excellent mechanical properties and thermal stability, especially for high-temperature applications, where the processing of RHEAs plays a critical role in engineering applications. In this work, the wire electrical discharge machining (WEDM) performance of WNbMoTaZrx (x = 0.5, 1) RHEAs was investigated, as compared with tungsten, cemented carbide and industrial pure Zr. The cutting efficiency (CE) of the five materials was significantly dependent on the melting points, while the surface roughness (Ra) was not. For the RHEAs, the CE was significantly affected by the pulse-on time (ON), pulse-off time (OFF) and peak current (IP), while the surface roughness was mainly dependent on the ON and IP. The statistical analyses have shown that the CE data of RHEAs have relatively-smaller Weibull moduli than those for the Ra data, which suggests that the CE of RHEAs can be tuned by optimizing the processing parameters. However, it is challenging to tune the surface roughness of RHEAs by tailoring the processing parameters. Differing from the comparative materials, the WEDMed surfaces of the RHEAs showed dense spherical re-solidified particles at upper recast layers, resulting in larger Ra values. The proportion of the upper recast layers can be estimated by the specific discharge energy (SDE). Following the WEDM, the RHEAs maintained the main BCC1 phase, enriched with the W and Ta elements, while the second BCC2 phase in the Zr1.0 RHEA disappeared. Strategies for achieving a better WEDMed surface quality of RHEAs were also proposed and discussed.

Analysis of Particle Size and Concentration in Die Sinking Electric Discharge Machining.

Electric discharge machining with a powder mix dielectric is a promising technique to harden a work piece's surface using electricity with a high energy density. The quality of the electrical discharge-machined surface is related to its surface integrity in which the surface's roughness, residual stresses, micro hardness and surface micro cracks are some of the major factors. In this research, graphite powder was mixed in a dielectric with a particle size of 20 µm, 30 µm, and 40 µm, with the concentration of the graphite powder ranging from 2 g/L to 4 g/L. Moreover, the peak current and pulse time on were also coupled with an additive of graphite powder to investigate the effect on the surface quality, i.e., the recast layer thickness, micro hardness and crater depth as well as the material removal rate (MRR) and tool wear rate (TWR). A Box-Behnken design was employed to design the experiments and the experimental results revealed that the graphite powder size and concentration coupled with the electrical parameters (peak current and pulse time on) significantly influenced the recast layer thickness, micro hardness, crater size, MRR and TWR. The crater depth and micro hardness were maximized at a higher concentration and particle size, while the recast layer thickness was reduced with a higher gain size.

Recycling Vanadium and Proton-Exchange Membranes from Waste Vanadium Flow Batteries through Ion Exchange and Recast Methods.

This study aims to provide a system to recycle vanadium resources and recover membranes from waste proton-exchange membranes. This research is divided into two parts. To begin, ion exchange batch and column experiments were applied to adsorb vanadium in a membrane. In this process, the waste membrane was initially dissolved in a 50% ethanol solution, and the suspension obtained by dispersing the membrane had 74 mg/L of vanadium. Then, Dowex G26 resin was used to adsorb vanadium from the membrane dispersion in the ion-exchange process. The adsorptive behavior and optimal parameters were explored in this study. The vanadium ions were then eluted by HCl to obtain an enrichment solution, and the V2O5 was received through precipitation and calcination methods. After obtaining the vanadium-free dispersion, the recycled membrane was prepared by recasting it in the second part. The characteristics of the recycled membrane, such as the moisture, FTIR spectra, ion-exchange capacity, and ion conductivity, are discussed. The results revealed that the adsorption capacity of vanadium through Dowex G26 was 81.86 mg/g. The eluting efficiency of HCl was 97.5%, and the optimal parameters of the precipitation and calcination processes were set as pH 5, NH4Cl:V = 2:1, and 350 °C. The moisture of the recycled membrane was 25.98%, and the IEC was 0.565 meq/g. The consequences of FTIR and ion conductivity demonstrated that the vanadium in the recycled membrane was eliminated by the ion-exchange method; however, the microstructure of the recycled membrane was influenced during ion exchange and recasting.

Study on Solidification Process and Residual Stress of SiCp/Al Composites in EDM.

To study the change of residual stress during heating and solidification of SiCp/Al composites, a one-way FSI (Fluid Structure Interaction) model for the solidification process of the molten material is presented. The model used process parameters to obtain the temperature distribution, liquid and solid-state material transformation, and residual stress. The crack initiated by the thermal stress in the recast layer was investigated, and a mathematical model of crack tip stress was proposed. The results showed a wide range of residual stresses from 44 MPa to 404 MPa. The model is validated using experimental data with three points on the surface layer.

Reviewing Performance Measures of the Die-Sinking Electrical Discharge Machining Process: Challenges and Future Scopes.

The most well-known and widely used non-traditional manufacturing method is electrical discharge machining (EDM). It is well-known for its ability to cut rigid materials and high-temperature alloys that are difficult to machine with traditional methods. The significant challenges encountered in EDM are high tool wear rate, low material removal rate, and high surface roughness caused by the continuous electric spark generated between the tool and the workpiece. Researchers have reported using a variety of approaches to overcome this challenge, such as combining the die-sinking EDM process with cryogenic treatment, cryogenic cooling, powder-mixed processing, ultrasonic assistance, and other methods. This paper examines the results of these association techniques on various performance measures, such as material removal rate (MRR), tool wear rate (TWR), surface roughness, surface integrity, and recast layer formed during machining, and identifies potential gap areas and proposes a solution. The manuscript is useful for improving performance and introducing new resolutions to the field of EDM machining.

A Soft Computing-Based Analysis of Cutting Rate and Recast Layer Thickness for AZ31 Alloy on WEDM Using RSM-MOPSO.

In the present research, the AZ31 alloy is machined by wire-cut electric discharge machining (WEDM). The experiments were designed according to the Box-Behnken design (BBD) of response surface methodology (RSM). The input process variables, namely servo feed (SF), pulse on-time (Ton), servo voltage (SV), and pulse off-time (Toff), were planned by BBD, and experiments were performed to investigate the cutting rate (CR) and recast layer thickness (RCL). The analysis of variance (ANOVA) was performed to determine the influence of machining variables on response characteristics. The empirical models developed for CR and RCL were solved using Multi-Objective Particle Swarm Optimization (MOPSO). Pareto optimal front is used for the collective optimization of CR and RCL. The optimal solution suggested by the hybrid approach of RSM-MOPSO is further verified using a confirmation test on the random setting indicated by the hybrid algorithm. It is found that the minimum RCL (6.34 µm) is obtained at SF: 1700; SV: 51 V; Toff: 10.5 µs; and Ton: 0.5 µs. However, maximum CR (3.18 m/min) is predicted at SF: 1900; SV: 40 V; Toff: 7 µs; and Ton: 0.9 µs. The error percentage of ±5.3% between the experimental results and predicted solutions confirms the suitability of the proposed hybrid approach for WEDM of AZ31.

Prompting for repair as a language teaching strategy for augmentative and alternative communication.

Conversational repair has been found to play a fundamental role in the acquisition of language. This paper describes existing research on conversational repair and its relationship to language learning, whether a first language or a second language, as well as its relevance to augmentative and alternative communication (AAC). A case is made for incorporating prompts to repair in conversation-based language interventions with children learning to use AAC. We argue that interventions targeting linguistic complexity should encourage self-repair in conversation in order to develop linguistic and operational competency as well as increase automaticity when using AAC. Clinical implications and directions for future research are discussed.

Laser Beam Drilling of Inconel 718 and Its Effect on Mechanical Properties Determined by Static Uniaxial Tensile Testing at Room and Elevated Temperatures.

Particularly in the aerospace industry and its applications, recast layers and microcracks in base materials are considered to be undesirable side effects of the laser beam machining process, and can have a significant influence on the resulting material behavior and its properties. The paper deals with the evaluation of the affected areas of the Inconel 718 nickel-base superalloy after its drilling by a laser beam. In addition, measurements and analyses of the mechanical properties were performed to investigate how these material properties were affected. It is supposed that the mechanical properties of the base material will be negatively affected by this accompanying machining process phenomenon. As a verification method of the final mechanical properties of the material, static uniaxial tension tests were performed on experimental flat shape samples made of the same material (Inconel 718) and three different thicknesses (0.5/1.0/1.6 mm) which best represented the practical needs of aerospace sheet metal applications. There was one hole that was drilled with an angle of under 70° in the middle of the sample length. Additionally, there were several sets of samples for each material thickness that were drilled by both conventional and nonconventional methods to emphasize the effect of the recast layer on the base material. In total, 192 samples were evaluated within the experiment. Moreover, different tensile testing temperatures (room as 23 °C and elevated as 550 °C) were determined for all the circumstances of the individual experiments to simulate real operation load material behavior. As a result, the dependencies between the amount of the recast layer and the length of the microcracks observed after the material was machined by laser beam, and the decrease in the mechanical properties of the base material, were determined.

How the Morphology of Nafion-Based Membranes Affects Proton Transport.

This work represents a systematic and in-depth study of how Nafion 1100 membrane preparation procedures affect both the morphology of the polymeric film and the proton transport properties of the electrolyte. The membrane preparation procedure has non-negligible consequences on the performance of the proton-exchange membrane fuel cells (PEMFC) that operate within a wide temperature range (up to 120 °C). A comparison between commercial membranes (Nafion 117 and Nafion 212) and Nafion membranes prepared by three different procedures, namely (a) Nafion-recast, (b) Nafion uncrystallized, and (c) Nafion 117-oriented, was conducted. Electrochemical Impedance Spectroscopy (EIS) and Pulsed-field gradient nuclear magnetic resonance (PFG-NMR) investigations indicated that an anisotropic morphology could be achieved when a Nafion 117 membrane was forced to expand between two fixed and nondeformable surfaces. This anisotropy increased from ~20% in the commercial membrane up to 106% in the pressed membrane, where the ionic clusters were averagely oriented (Nafion 117-oriented) parallel to the surface, leading to a strong directionality in proton transport. Among the membranes obtained by solution-cast, which generally exhibited isotropic proton transport behavior, the Nafion uncrystallized membrane showed the lowest water diffusion coefficients and conductivities, highlighting the correlation between low crystallinity and a more branched and tortuous structure of hydrophilic channels. Finally, the dynamic mechanical analysis (DMA) tests demonstrated the poor elastic modulus for both uncrystallized and oriented membranes, which should be avoided in high-temperature fuel cells.

Parametric evaluation of electrical discharge coatings on nickel-titanium shape memory alloy in deionized water.

Nickel-titanium shape memory alloy (NiTi) has a unique capacity to restore its initial shape after deformation, which is highly applicable to orthopaedic implantations, especially for the minimization of invasive surgeries. The high nickel content of this alloy can lead to unfavourable effects on the human body upon dissolution; thus, a reliable barrier of coatings on the NiTi surface is required to alleviate the nickel migration and increase its biocompatibility. In this paper, analyses of a titanium oxide layer development on NiTi surface using electrical discharge coating (EDC) process is presented. The recast layer thickness, crater sizes, and surface roughness were characterized based on five parameters; polarity, discharge duration, pulse interval, peak current, and gap voltage. The results show that the discharge duration is the most significant parameter to influence all responses, followed by peak current. The surface characteristics of the EDC substrate is depending on the crater formations and is highly correlated with the discharge energy intensity. As a result, appropriate parametric conditions of the electrical discharge coating process can enhance the NiTi surface for future medical applications, without compromising the shape memory effect.

On the Investigation of Surface Integrity of Ti6Al4V ELI Using Si-Mixed Electric Discharge Machining.

Surface modification is given vital importance in the biomedical industry to cope with surface tissue growth problems. Conventionally, basic surface treatment methods are used which include physical and chemical deposition. The major drawbacks associated with these methods are excessive cost and poor adhesion of coating with implant material. To generate a bioactive surface on an implant, electric discharge machining (EDM) is a promising and emerging technology which simultaneously serves as machining and surface modification technique. Besides the surface topology, implant material plays a very important role in surgical applications. From various implant materials, titanium (Ti6Al4V ELI) alloy is the best choice for long-term hard body tissue replacement due to its superior engineering, excellent biocompatibility and antibacterial properties. In this research, EDM's surface characteristics are explored using Si powder mixed in dielectric on Ti6Al4V ELI. The effect of powder concentration (5 g/L, 10 g/L and 20 g/L) along with pulse current and pulse on time is investigated on micro and nanoscale surface topography. Optimized process parameters having a 5 g/L powder concentration result in 2.76 µm surface roughness and 13.80 µm recast layer thickness. Furthermore, a nano-structured (50-200 nm) biocompatible surface is fabricated on the surface for better cell attachment and growth. A highly favourable carbon enriched surface is confirmed through EDS which increases adhesion and proliferation of human osteoblasts.

Recast type, repair, and acquisition in AAC mediated interaction.

The present study investigated the effects of different types of recasts and prompts on the rate of repair and spontaneous use of novel vocabulary by eight children with severe motor speech disabilities who used speech-generating technologies to communicate. Data came from 60 transcripts of clinical sessions that were part of a conversation-based intervention designed to teach them pronouns, verbs, and verb inflections. The results showed that, when presented alone, interrogative choice and declarative recasts led to the highest rates of child repair. The results also showed that when children were presented with recasts and prompts to repair, the rate of repair increased. Spontaneous use of linguistic targets was significantly and positively related to conversational sequences where the adult recast was followed by child repair. These findings suggest that using different recast types and prompts to repair may be beneficial for spontaneous use of linguistic targets in this population.