Microhardness Research Articles

Simultaneous optimization of machine and tool parameters for EDM using WC/Co P/M electrode made with micron and nano sized particles

Multi-response characteristic optimization is the most desired aspect of the components produced from electric discharge machining (EDM). Obtaining the optimal combination of parameters for surface roughness (SR) and micro-hardness (MH) is always a challenging task as the machining parameters favourable to one performance measure adversely affects the other. The present paper deals with the simultaneous optimization of SR and MH of D2 alloy steel during EDM with tungsten carbide (WC)/cobalt (Co) P/M electrode by considering electrode and machine tool parameters. Experimental run order was planned with Taguchi’s orthogonal arrays (OA) and in the present investigation, it is based on L18 OA. The analysis of variance (ANOVA) performed for the grey relational grade (GRG) showed that the tool parameter “particle size” (PS) is the most influential factor (61.43%) for simultaneous improvement of performance measures. The P/M electrode made of fine particle size (i.e., at nano level) has improved the process stability and reduced the arcing and short-circuiting results in reduced surface roughness. Simultaneously, the formation of the hard intermetallic phase’s viz., Fe3C, Cr23C6, W2C, Fe6W6C, and Cr2Fe14C on the EDMed surface has increased the surface hardness. The optimal set of parameters was validated through confirmation experiments.

Experimental investigation and performance enhancements characteristics of gaseous assisted powder mixed near dry electric discharge machining

Gaseous assisted powder mixed near dry EDM (GAPMND-EDM) is one of the recent hybrid technologies, which not only enhance the machining performance, but at the same time, high quality products with better surface quality characteristics can also be achieved. In this study, the response parameters were material removal rate, surface finish, micro hardness and residual stress. It was found that the maximum material removal rate (MRR 3.379 mg/min) was achieved with combination of (dielectric) oxygen gas with graphite powder while lowest surface roughness (SR 1.11 μm) was found to be with dielectric argon gas with graphite additives. Highest micro hardness (MH) and lowest residual stress (RS) was 820.30 Vickers hardness number (VHN) and 229 MPa found with dielectric combination of zinc additives with argon gas.

Implementation of Jaya algorithm for process parameter optimization during EDM processing of NiTi 60alloy

Electrical Discharge Machining (EDM) process is an advanced machining process used in wide range of manufacturing applications especially for hard materials. Functioning and quality of EDMed machined parts/components plays important role when put to the service. For this not only selection of optimum machining process but also selection of effective optimization technique need to be given special attention. With this intention the target of the current research is to survey the different optimization techniques (Response surface, Taguchi, Grey regression analysis, Artificial nueral network etc.), research gap indicates scope for implementation of Jaya algorithm which is a modern optimization technique. With use of Jaya algorithm technique research work was carried out to evaluate white layer thickness (WLT) and micro hardness (MH) as output parameters during EDM machining of NiTi60 alloy. These output parameters were evaluated with variations in input process parameters considering voltage (V), current (C), pulse on (Pon) and pulse off (Poff) time. The experiments were conducted using L9 Taguchi orthogonal array and mathematical predictions models were generated using regression analysis. Jaya algorithms were developed with the intention to minimize the WLT and minimize the MH as the objective functions. It is concluded that Jaya optimization technique can be effectively implemented to optimize the process parameters in EDM process which shows considerable reductions in WLT from 5.914 to 4.947 µm and MH from 208.71 to 200.3 respectively.

Machinability studies of lead induced Ti-6Al-4V alloy using Taguchi technique on WEDM process

The advanced materials such as Titanium alloys have been used in aerospace, spacecraft and missile applications, due to their high tensile strength and ability to withstand high temperatures. In the present investigation, wire electrical discharge machining process (WEDM) has been used for machining of Lead induced Ti-6Al-4V. The experiments were conducted based on Taguchi L27 orthogonal array. The input factors namely current (Ip), pulse-on-time (Ton), servo voltage (SV) and pulse-off-time (Toff) were used and varied in order to observe cutting speed (CS), surface roughness (Ra), dimensional deviation (DD), recast layer thickness (RLT), micro hardness (MH) and surface integrity characteristics of machined component. Finally, the surface topography of alloys has been examined on the optimum conditions of performance characteristics WEDM samples.

Effect of heat treatment process on hardness and hot corrosion resistance of Fe-25Ni-18Cr-1Mo-2 W-1Nb-Cast austenitic stainless steel

Abstract This paper reports the effect of heat treatment process on hardness and hot corrosion resistance of Fe-25Ni-18Cr-1Mo-2 W-1Nb-cast austenite stainless steel. The steels were prepared by a process sequence of induction melting, hot rolled, solution treatment and aging. The solution treatment process carried out at a temperature of 975, 1025 and 1075 °C for 2 h and quench in the water and aging process carried out at 775 °C for 8, 16 and 24 h and quench in the air. The Optical Microscope (OM) observation and hardness micro Vickers test were carried out in the steels after process of heat treatment. Then, the steels were tested hot corrosion in the melting salt at a temperature of 800 °C for 4, 8, 12, 16 and 24 h. The weight loss of the steels due to hot corrosion test was calculated and analysis. The Scanning Electron Microscope (SEM), Energy Dispersive Spectrometry (EDS) and mapping of elements were used for analyses of corrosion products of the steels. The results show that the higher hardness value was found in solution treatment of 975 °C and aging for 16 h and the higher hot corrosion resistance was found in solution treatment of 1025 °C and aging 16 h.

Effect of the application of different concentrations of EDTA on the adhesion of fiber posts using self-adhesive cements.

The purpose of this study was to analyze the effect of the application of different concentrations of EDTA on the adhesion of fiber posts to root dentin using self-adhesive resin cements. After endodontic treatment, 78 single roots were randomly divided into six groups (n = 13) according to the combination of the following factors: surface dentin treatment - control (distilled water), 17% EDTA and 24% EDTA; and self-adhesive resin cement - RelyX U200 (RX); and Multilink Speed (ML). After fiber post cementation, six slices were obtained for each root. Ten roots of each group were used for bond strength (BS) and three for microhardness (MH) evaluations. Data obtained from BS and MH tests for each resin cement were subjected to two-way ANOVA (surface treatment vs. root region) and to a post-hoc Tukey's test (α = 0.05). The lowest BS value was observed in the 24% EDTA group for RX cement, whereas the highest values for ML cement were observed for the control group in the middle and apical regions. In the MH test, the lowest value for RX was observed for 24% EDTA in the cervical region, whereas and the highest value for the ML cement was observed in the control group. Regarding both self-adhesive resin cements tested, the application of 24% EDTA was not able to improve the adhesion of fiber posts to root canal.

Composites Based on Poly(Lactic Acid) (PLA) and SBA-15: Effect of Mesoporous Silica on Thermal Stability and on Isothermal Crystallization from Either Glass or Molten State.

Several composites based on an L-rich poly(lactic acid) (PLA) with different contents of mesoporous Santa Barbara Amorphous (SBA-15) silica were prepared in order to evaluate the effect of the mesoporous silica on the resultant PLA materials by examining morphological aspects, changes in PLA phases and their transitions, and, primarily, the influence on some final properties. Melt extrusion was chosen for the obtainment of the composites, followed by quenching from the melt to prepare films. Completely amorphous samples were then attained, as deduced from X-ray diffraction and differential scanning calorimetry (DSC) analyses. Thermogravimetric analysis (TGA) results demonstrated that the presence of SBA-15 particles in the PLA matrix did not exert any significant influence on the thermal decomposition of these composites. An important nucleation effect of the silica was found in PLA, especially under isothermal crystallization either from the melt or from its glassy state. As expected, isothermal crystallization from the glass was considerably faster than from the molten state, and these high differences were also responsible for a more considerable nucleating role of SBA-15 when crystallizing from the melt. It is remarkable that the PLA under analysis showed very close temperatures for cold crystallization and its subsequent melting. Moreover, the type of developed polymorphs did not accomplish the common rules previously described in the literature. Thus, all the isothermal experiments led to exclusive formation of the α modification, and the observation of the α’ crystals required the annealing for long times at temperatures below 80 °C, as ascertained by both DSC and X-ray diffraction experiments. Finally, microhardness (MH) measurements indicated a competition between the PLA physical aging and the silica reinforcement effect in the as-processed amorphous films. Physical aging in the neat PLA was much more important than in the PLA matrix that constituted the composites. Accordingly, the MH trend with SBA-15 content was strongly dependent on aging times.

A STUDY ON DEPOSITION OF ELECTRODE MATERIALS ON MAGNESIUM ALLOY USING ELECTRICAL DISCHARGE COATING TECHNIQUE

In this present research, an attempt has been made to deposit the WC/Cu composite coating on the ZE41A magnesium alloy using electrical discharge coating technique. Tungsten carbide and copper powders with a particle size of 4 μm were used as the electrode materials. Electrodes are prepared in the combination of WC70: Cu30 under different load (150 MPa, 175 MPa, 200 MPa) using powder metallurgy technique. In this experiment, compaction pressure, current and pulse on time were selected as the input process parameters and response were material deposition rate (MDR), layer thickness (LT) and microhardness (MH). From the results, it was revealed that the MDR, LT and MH increase with an increase in discharge current and pulse on time and decreases with increases in compaction pressure. Microstructural evaluation on the deposited surface was performed by using scanning electron microscopy (SEM). More prominent craters formed in the deposited region results in the lower surface finish. Energy dispersive spectroscope (EDS) test was carried out to confirm the electrode materials deposited on the workpiece surface.

Performance analysis of Cu-W-B4C composite tool during electrical discharge machining of titanium alloy

Electrical discharge machining (EDM) is broadly used in machining of parts having intricate shapes made of difficult-to-machine materials. During EDM, tool fabrication time through conventional machining processes is generally excessively high. Therefore, alternate tool material and fabrication strategy is sought to reduce machining lead time. In this work, composite tools made of copper, tungsten and boron carbide have been prepared through powder metallurgy (PM) route. The performance of these tools is studied during machining of titanium alloy work piece. The input parameter considered are tool material parameters such as weight percentage of tungsten and boron carbide in the tool and machining parameters like peak current, pulse-on-time and duty cycle. The performance of these tools are evaluated considering the performance measures such as material removal rate (MRR), tool wear rate (TWR), average surface roughness (Ra), surface crack density (SCD), white layer thickness (WLT) and micro-hardness (MH). It is observed that the tool materials have been transferred onto the machined surface forming a hard layer with increased weight percentage of oxygen and carbon during machining. The PM tools exhibit similar performance as solid copper tool with respect to MRR, TWR and surface integrity.

Effect of sintered electrode on microhardness and microstructure in electro discharge deposition of magnesium alloy

Abstract In this study, an endeavour have been made to depositing the electrode materials over the surface of the magnesium alloy using electrical discharge machining (EDM) with WC-Cu powder compacted sintered electrode. Various process parameters such as compaction load, discharge current and pulse on time are selected to carry out the experiment in order to attain the maximum material migration rate (MMR) or deposition rate and microhardness (MH). It was concluded that the MMR and MH increased with increase in discharge current and pulse on time at low compacted electrode but it is decreased at lower discharge current and pulse on time. Highest MMR and MH were attained successfully at partial sintered low compaction load electrode. Microstructure evaluation has been carried out on deposited surface using scanning electron microscopy (SEM) and presence of electrode element in the deposited surface was confirmed by energy dispersive spectroscopy (EDS). Defects mechanism such as globules and craters are formed during EDC with high current and pulse on time respectively, which diminishes the surface roughness. It was observed that the compaction load is the influence parameter on the MMR and MH.

Statistical Optimization by the Response Surface Methodology of Direct Recycled Aluminum-Alumina Metal Matrix Composite (MMC-AlR) Employing the Metal Forming Process

In this study, the response surface methodology (RSM) and desirability function (DF) were utilized to optimize the recycling conditions of aluminum (AA6061) chips, in the presence of particulate alumina (Al2O3), to obtain a metal matrix composite of recycled aluminum (MMC-AlR) using hot press forging processes. The effects of temperature (430–530 °C) and holding time (60–120 min) were investigated. The introduction of 2.0 wt. % of Al2O3 to the aluminum matrix was based on preliminary research and some pilot tests. This study employed the 2k factorial design of experiments that should satisfy the operating temperatures (T) of 430 °C and 530 °C with holding times (t) of 60 min and 120 min. The central composite design (CCD) was utilized for RSM with the axial and center point to evaluate the responses to the ultimate tensile strength (UTS), elongation to failure (ETF), and microhardness (MH). Based on RSM, with the desirability of 97.6%, the significant parameters T = 530 °C and t = 120 min were suggested to yield an optimized composite performance with UTS = 317.99 MPa, ETF = 20.45%, and MH = 86.656 HV. Three confirmation runs were performed based on the suggested optimum parameters, and the error revealed was less than 25%. The mathematical models suggested by RSM could adequately describe the MMC-AlR responses of the factors being investigated.

Vickers Hardness and Shrinkage Stress Evaluation of Low and High Viscosity Bulk-Fill Resin Composite.

The aim of this in vitro study was to evaluate the hardness and shrinkage stress (SS) of six bulk-fill resin composites. To evaluate microhardness (MH), ten 6 mm specimens were prepared using a metal mold for each selected bulk-fill resin composite and irradiated from the top side for 40 s using an LED light. After 24 h of storage, Vickers MH was evaluated on the upper, lower and lateral sides of the specimens. SS evaluation was then performed with a universal machine, which evaluated the contraction force generated by a bulk-fill composite specimen placed between two metal cylinders during and after light curing. The results were evaluated with a one-way ANOVA test with a post-hoc Bonferroni test and linear regression analysis (p < 0.05). All materials showed a significant MH decrease between the top and bottom surfaces. However, the bulk-fill materials tested performed differently when considering lateral depth progression. ANOVA tests for SS evaluation showed that both SDR and Venus Bulk Fill had significantly lower stress during irradiation than other tested materials. Further, MH decrease became significantly lower from the top surface at different depths in each tested group. Among the different resins, Venus Bulk Fill and SDR showed not only inferior hardness, but also a significant reduction in SS.

The effect of rapid high-intensity light-curing on micromechanical properties of bulk-fill and conventional resin composites

Rapid high-intensity light-curing of dental resin composites is attractive from a clinical standpoint due to the prospect of time-savings. This study compared the effect of high-intensity (3 s with 3,440 mW/cm2) and conventional (10 s with 1,340 mW/cm2) light-curing on micromechanical properties of conventional and bulk-fill resin composites, including two composites specifically designed for high-intensity curing. Composite specimens were prepared in clinically realistic layer thicknesses. Microhardness (MH) was measured on the top and bottom surfaces of composite specimens 24 h after light-curing (initial MH), and after subsequent immersion for 24 h in absolute ethanol (ethanol MH). Bottom/top ratio for initial MH was calculated as a measure of depth-dependent curing effectiveness, whereas ethanol/initial MH ratio was calculated as a measure of crosslinking density. High-intensity light-curing showed a complex material-dependent effect on micromechanical properties. Most of the sculptable composites showed no effect of the curing protocol on initial MH, whereas flowable composites showed 11–48% lower initial MH for high-intensity curing. Ethanol/initial MH ratios were improved by high-intensity curing in flowable composites (up to 30%) but diminished in sculptable composites (up to 15%). Due to its mixed effect on MH and crosslinking density in flowable composites, high-intensity curing should be used with caution in clinical work.

EDMed Inconel 718 using powder metallurgy (P/M) sintered electrode made with nano and micron sized powders

This work presents experimental data carried out for surface modification of Inconel 718 using WC/Cu composite powder metallurgy (P/M) electrodes made of nano and micron sized particles. Both machine and tool parameters were selected for study and experiments were planned as per Taguchi’s L18 mixed orthogonal array in order to find the influence of parameters on surface roughness (SR) and micro-hardness (MH). Peak current, particle size and pulse on time were found to be most significant on both SR and MH. High reactive surface area of nano particles made surface alloying greater than the other tool electrodes and has shown its influence positively on both SR and MH. The EDX analysis reveals the migration of WC and Cu elements and deposition of carbon and oxygen particles on the surface. The XRD spectrum confirms presence of carbides (WC, W2C, Fe5C2, Cr7C3, Fe7C3 and Fe3C), oxides (Fe3O4, WO3 and Cr3O) and other intermetallics at different machining conditions indicating the influence of Pulse on time (TON) and Peak current (IP) on discharge energies and in turn on the properties of machined surface. The carbides generated on the machined surface increased the hardness to 845HV without much sacrifice of the roughness of the machined surface. The range of roughness values obtained in the present investigation is 2.443 to 4.098µm.

Assessment on the microhardness and corrosion resistance characteristics of Ni-SiC and Ni-MWCNT coatings by pulse reverse electrodeposition technique

The characteristics of Silicon carbide (SiC) and multi-walled carbon nanotube (MWCNT) nano composite coatings by a Pulse Reverse Electrodeposition (PRE) method is investigated in detail to enhance the microhardness (MH) and corrosion resistance characteristics of AISI 304 stainless steel substrate. The electrodeposition nature, dissolution behavior, surface characteristics are assessed by Scanning Electron Microscopy (SEM) with energy dispersive x-ray (EDX), x-Ray Diffraction (XRD), Atomic Force Microscopy (AFM), Microhardness (MH) Test and Electrochemical studies. The coatings are prepared in the watts type bath using pulse reverse electrodepositions (PRE) method of varying the electrolyte deposition parameters in different combinations. Present results clearly reveal that, there is a drastic improvement in the magnitude of microhardness of coated specimens, silicon carbide (SiC) and multi-walled carbon nanotube (MWCNT) composite coatings yield a maximum hike of 91.6% and 168% respectively. Furthermore, the Nyquist and impedance plots clearly depict that, multi-walled carbon nanotube (MWCNT) exhibits higher corrosion resistance characteristics.

Study on the Influence of Metallic Powder in Near-Dry Electric Discharge Machining

Near-dry electrical discharge machining (ND-EDM) is an eco-friendly process. In this study, an approach has been made to make the machining process more efficient than ND-EDM with the addition of metallic powder with the dielectric medium to machine EN-31 die steel. Powdermixed near-dry EDM (PMND-EDM) has several advantages over the ND-EDM or conventional electrical discharge machining (EDM) process, such as a higher material removal rate (MRR), fine surface finish (Ra), sharp cutting edge, lesser recast layer, and lower deposition of debris. The output response variables are MRR, Ra, residual stress (RS) and micro-hardness (MH) of the machined surfaces. Further study of the workpiece was performed, and a comparative study was conducted between ND-EDM and PMND-EDM. In this proposed method of machining, the MRR, Ra, and MH increased by 17.85 %, 16.36 %, and 62.69 % while RS was reduced by 56.09 %.

Mechanical characterization of aged AA2026-AA2026 overcast joints fabricated by squeeze casting

Squeeze overcasting has emerged as an attractive option for casting of Al alloys in terms of mechanical properties. The attainment of the desired magnitude of these properties is challenging in overcasting due to the involvement of a number of process parameters. In this study, the effects of insert preheat temperature (TI) along with pouring temperature (TP), and squeeze pressure (PS) on the mechanical properties of squeeze overcast AA2026-AA2026 joint were investigated. Experimental results revealed that the squeeze pressure is the most prominent factor affecting the ultimate tensile strength (UTS) while micro-hardness (MH) is significantly influenced by the pouring temperature. Maximum values of UTS (315 MPa) and MH (130 HV) were achieved at a PS of 120 MPa, TP of 780 °C, and TI of 250 °C. Energy dispersive X-ray (EDX) analysis witnessed that TI has also a significant role in determining the quality of bond between the substrate and the melt. Scanning electron microscopy (SEM) depicts that the morphology of the fractured surface has a sound influence on both selected responses. Both the strength and hardness are noticed better if the fractured surface possesses the flat-faced morphology. Furthermore, an empirical regression model was developed using response surface methodology (RSM) design and validated through eight confirmatory experiments. RSM integrated multi-objective optimization genetic algorithm (MO-GA) was deployed to optimize the UTS and MH. The comparative results obtained from RSM and MO-GA demonstrated that the deviation in experimental and predicted values is less than 5%.

Effect of nano-strengthening on the properties and microstructure of recycled concrete

Abstract Influence of nano-strengthening immersion on the properties of recycled aggregate (RA) and recycled aggregate concrete (RAC) and the microstructure of interfacial transition zones (ITZs) between mortar and aggregate were studied in this paper. Results showed that nano-strengthening immersion was helpful to reduce the crushing value and total pore area of RA, to significantly improve the mechanical strength of RAC, and to modify the bond strength between RAC and steel rebar and the structural properties of RAC beams. Mercury intrusion porosimetry (MIP), micro-hardness (MH) and scanning electron microscope (SEM) observation were conducted in order to reveal the enhancement mechanism of nano-strengthening immersion. Results showed that the density and mechanical properties in ITZs were obviously improved by nano-strengthening because the coating and penetration of nano-materials was helpful to block the pores and cracks in ITZs, to avoid the directed gathering of CH crystal, and to accelerate the hydration of cement and mineral additions.

Dentin Microhardness and Sealer Bond Strength to Root Dentin are Affected by Using Bioactive Glasses as Intracanal Medication.

This study investigated the human dentin microhardness (MH) and the MTA Fillapex® (Fillapex) and AH Plus®(AH) bond strength (BS) to dentin after using calcium hydroxide (Ca(OH)2) and bioactive glasses (45S5 and an experimental niobium phosphate bioactive glass (NbG)) as intracanal medications. For the MH test dentin slices were filled with medications and were submitted to Knoop MH (KHN) test (at day-0 (baseline data/without medication) and at day-15 (after using medication)). For the BS test, after medications had remained for 15 days in the roots, dentin slices were obtained and filled with the sealers. Seven days later, sealer BS to dentin was measured by push-out test (MPa). Data were statistically analyzed. Failure mode was visually assessed. The use of NbG, 45S5 for 15 days, increased the dentin MH and reduced the BS between AH sealer and dentin, but did not interfere with the Fillapex BS.

Experimental Investigation and Optimization of Process Parameters in Laser welding of NiTinol Shape Memory Alloys

Abstract In this work, an attempt was made to conduct bead on plate welding of NiTinol Shape memory alloy utilizing Yb: YAG laser welding process and identify the optimized parameters using Deng’s Similarity based approach integrated with Entropy Weight Method. Bead on Plate welding was carried out based on L9 Taguchi array with laser power, focal position, shielding gas blown distance and welding speed as input parameters. Bead width (BW), depth of penetration (DOP), microhardness (MH), and corrosion current density were measured as output parameters. Entropy weight method was first utilized to determine the weights that had to be given to output parameter, and Deng’s similarity based approach was used to find the optimized welding parameter combinations. The metallurgical characterization of the optimized weld was discussed with the aid of microstructure. Entropy weight Method results suggested to give more importance to microhardness. Deng’s Similarity approach identified that the 7th experimental (welding speed = 2400 mm/min, shielding gas blown distance = 8mm, focal position= 0.5 mm, power = 900 W) run as the optimized parameter combination for getting the weld with full penetration, lesser bead width, higher microhardness and corrosion resistance