Microwave Hybrid Heating Research Articles

Effect of powder size in microwave joining of oxygen-free copper to SS304

This paper investigates the prospect of microwave hybrid heating to join oxygen-free copper with stainless steel (SS304). The effect of size of copper (Cu) powder interlayer in the microstructure and mechanical properties of the joint formed is investigated, along with the incites on the mechanism of joint formation. Cu powder of average sizes 4 and 45 μm was studied. The microwave heating rate was observed to be high for 4 μm Cu in the absence of voids or porosities in the joint region. Voids were observed in the interlayer when 45 μm Cu powder was used. The joint was formed due to volumetric diffusion of the major elements of the substrates, e.g. Fe, Cu, Cr that was verified by energy dispersive spectroscopy. Oxides were present for 45 μm Cu which was absent for 4 μm Cu. X-ray diffraction and energy-dispersive X-ray spectroscopy analysis concluded that no intermetallic compound was formed along the interlayer. The micro-hardness of ∼128 HV was observed to be uniform across the interlayer depicting a good metallurgical joint. The maximum tensile shear strength of 83.12 MPa was recorded for 4 μm copper powder and microwave time of 14 min, exhibiting ductile failure of the joint.

Microwave casting of stainless still through microwave hybrid heating

A microwave is defined as a form of electromagnetic radiation. The microwave has an electric-field and magnetic field and those fields are orthogonal to each other and within the frequency range of 0.3-300 GHz. Microwave casting is a novel technique to cast different materials using microwave hybrid heating (MHH). The microwave casting is divided into two parts, such as in-situ and ex-situ. In this paper, the in-situ microwave casting process is used to cast the SS316bulk metal. A domestic microwave applicator has a frequency of 2.45 GHz with a power capacity of 900W. Stainless steel was used as a powder form having a particle size of 40-80 μm. SEM, EDS, and micro-hardness of the casted samples are carried out to validate the casting of SS316 bulk metal. The modal analysis of casted beam using experimental OROS software technique to measure the natural frequencies, corresponding damping ratios, and damping capacity of the casted SS316 samples.

Microwave-prepared Ti/RuO2-IrO2 anodes: Influence of IrO2 content on atrazine removal

Electrochemical oxidation is a promising technology for treating wastewater, although the search for new efficient and economically viable electrode materials is still necessary. Within this context, mixed metal oxide anodes appear as excellent alternatives, but their formulation is still an important point to study, looking for obtaining low-cost materials with high electrocatalytic efficiencies. In the search for these highly-efficient anodes, here, we prepared three different coatings (RuO2)0.7(IrO2)0.3, (RuO2)0.8(IrO2)0.2, and (RuO2)0.9(IrO2)0.1 using microwave hybrid heating. All the prepared anodes exhibit excellent physical and electrochemical properties. However, as the proportion of IrO2 increases in the anode, the voltammetric charge and the contribution of the internal active sites increase, as well as the capacity for the electrochemical generation of hypochlorite ions. The electrochemical treatment of atrazine was performed using the synthesized electrodes and applying different current densities (20, 40, 60 mA cm–2). Faster and more efficient electrochemical oxidation occurs by applying 20 mA cm–2, regardless of the anode used, and the (RuO2)0.7(IrO2)0.3 anode reaches the best performance. Finally, an important figure of merit was analyzed, the electrical energy by one order of magnitude (EEO) used to remove atrazine. The anode (RuO2)0.7(IrO2)0.3 reduced the EEO down to two folds for the optimal current density (20 mA cm–2) compared with the other anodes studied, highlighting its good features for treating effluents contaminated with pesticides.

Processing and characterization of SS316 based metal matrix composite casting through microwave hybrid heating

In the current study, metal matrix composites of iron-based alloy (SS316) are successfully cast by the application of a novel processing route of microwave hybrid heating (MHH). The castings of iron-base alloy (SS316) powder and reinforced with 10 wt.% EWAC1004 (Ni-based) + 3 wt.% WC-12Co are developed in the domestic microwave oven power of 900 W and frequency 2.45 GHz. The mechanical and metallurgical properties of the prepared casts are investigated. The value of the mean particle size of the powder used is found to be 40 μm. Scanning electron microscopy (SEM), optical microscopy (OM), X-Ray diffraction (XRD), and Vickers’s microhardness tester are used for the characterization of so developed composites samples. The microstructure is reported as elongated columnar grains or lathlike structure with uniform melting of the iron-based (SS316) matrix has been achieved. The XRD confirmed the presence of typical carbides and intermetallic. The average micro-hardness of the reinforced composites is reported as 420 ± 90 HV0.3. The achieved microhardness of cast samples is 2 times the commercially received SS316. The micro-hardness obtained on the surface of the carbide phase is 648.16 HV0.3. The porosity of the prepared cast is found to be less than 2% which is approximately 3 times less as compared to commercially received SS316. The relative density of the microwave cast SS316 without reinforcement is found to be maximum with the value of 98%. The value of grain size of the microwave-casted composite samples is reduced to 23 microns (μm)

Assessment of microwave susceptors for optimum temperature rise using parametric numerical simulation

Microwave hybrid heating or indirect microwave heating has been an important development in the processing of metals using microwave energy. In this method of heating, a “susceptor” is used to absorb and convert microwave energy into thermal energy which is utilized for materials processing. Few of these processing applications are sintering, joining, cladding, casting, and composite development. However, the precise selection of a susceptor for a given process is challenging and requires a thorough understanding of the microwave heating phenomenon. In addition, predicting temperature rise in a microwave cavity is a complex task. Numerical simulation can serve to solve these two significant problems. In this work, parametric simulation of microwave heating of three major susceptor materials; silicon carbide, alumina, and coal has been carried out using a multiphysics approach. Initially, a model was developed to validate the simulation procedure. The results were in good agreement with the available data in published literature. Thereafter, the effect of microwave power, position of susceptor block, and time of irradiation on temperature rise in these materials were investigated. On comparing these susceptor blocks after altering the parametric combinations, coal exhibited the formation of hot spots and uneven temperature field with a maximum temperature of 901°C. On the contrary, the temperature attained in silicon carbide (529°C) and alumina (616°C) were lower but distributed in a relatively uniform field across the block. Regression models have also been built to correlate maximum temperature achieved with the parametric variation of parameters. It has been found that microwave power and the time of microwave irradiation have a significant coactive effect on the maximum temperature reached by the material. While the rise in the position of the susceptor block from the base leads to an adverse effect on the temperature rise. The study demonstrates that indirect microwave heating can be harnessed using the proper selection of susceptors as per the temperature requirement of the process. The regression models can be used for the accurate prediction of temperature attainment for given power input, position, and time.

Feasibility study on MoCoCrSi/WC-Co cladding developed on austenitic stainless steel using microwave hybrid heating

Partial dilution of clad powder and the substrate to form a new protective layer is called as cladding. The present article focuses on development of a novel surface modification technique for better resistance to wear/erosion using microwaves as the source of heat. Clads of MoCoCrSi/ WC-Co were produced on austenitic stainless steel (SS-316) using microwave irradiation techniques. Composite clads were established by irradiating microwaves at 2.45 GHz frequency and power of 900W using a domestic microwave applicator for a duration of 30 minutes. Characterization of the developed clads were performed in the form of metallographic(microstructure) and mechanical(hardness) tests. Careful observation of the microstructures revealed uniform grain structures, free from defects on the surface of the cladded substrate. Further, no significant cracks were to be found on the transverse section of the clad characterizing good bonding between clad particles and substrate. The developed clad demonstrates significantly higher hardness than the substrate.

A parametric study of conventional and high-speed microwave sintering of robocast porcelain

The combination of three-dimensional (3D) printing technologies and microwave (MW) sintering offers new perspectives for minimizing material, energy and time waste. This study aimed at conducting a parametric study on the sintering of robocast porcelain by conventional and MW heating in a multimode cavity (2.45 GHz, 3 kW). The effect of heating rate, dwell temperature and dwell duration on sample density, shrinkage and microstructure was investigated on small pellets. With conventional heating, a good densification was achieved with a 2 h dwell at 1250 °C, independent of heating rate (1–20 °C/min). A similar density was reached using microwave hybrid heating at a much higher heating rate (100 °C/min), shorter dwell (30 min) and slightly higher sintering temperature (1300 °C). Without susceptor, a longer pre-heating step was required to initiate the sample heating, thus extending the heat treatment duration. This study provides seeding data for the development of greener processes for aluminosilicate ceramic manufacturing.

Comparison of intermetallic compound growth and tensile behavior of Sn-3.0Ag-0.5Cu/Cu solder joints by conventional and microwave hybrid heating

Microwave hybrid heating (MHH) is a possible approach for soldering; yet, the long-term reliability of solder joints is still unclear. In this work, a comparative study was carried out on the influence of isothermal aging on SAC305/Cu solder joints by conventional reflow and MHH. The conventional reflow oven was set to 260 °C at 60 s holding time, and MHH was carried out at high operating power at 40 s. The reflowed sample was isothermally aged at 150 °C for various aging times (0, 240, 480 and 960 h) in a laboratory oven. The conventional reflow and MHH transformed the IMC structure from scallop-like to a planar-like Cu6Sn5 with a linear increase in thickness and a thin layer of Cu3Sn was observed at 240 h of aging. While Ag3Sn particles grew larger at longer aging time. The MHH shows a thinner Cu6Sn5 layer, and a smaller grain size compared to conventional reflow. The ultimate tensile strength (UTS) for conventional reflow (32.7 MPa) is 26.8% lower compared to MHH (44.7 MPa). The UTS for MHH is greater than conventional reflow as the isothermal aging time increases.

Microstructure and Tribological Characterization of Composite Castings Developed through In-situ Microwave Hybrid Heating

Microstructure and Tribological Characterization of Composite Castings Developed through In-situ Microwave Hybrid Heating

A comparative study of interface material through selective microwave hybrid heating for joining metal plates

The development of joints using microwave hybrid heating (MHH) received extensive attention over conventional heating due to its uniform heating, environment friendly characteristics. For effective microwave joining of bulk metals, joint region was targeted selectively naming it as selective microwave hybrid heating (SMHH). Microwave joining of stainless steel using Nickel as interface material is explored extensively through MHH; however no comparative study showing better interface material for microwave joining of Stainless steel is reported. In the present study, SS304-SS304 lap joint is simulated for two different interface materials that are nickel and Inconel-718 for an exposure time of 22 min. These joints were developed using pulverized charcoal as a susceptor material and at the power output of 700 W. Microwave hybrid heating has been simulated by implementing different assumptions and boundary conditions at better mesh quality. A time-temperature curve, resistive heating, electric field distribution, and temperature profile along different directions are those parameters that have been discussed to examine better interface material. From the results, it is observed that Inconel-718 shows better resistive heating when compared to nickel interface material, however electric field distribution remains similar for both interface materials. Further, the time-temperature profile revealed that the time taken for Inconel-718 interface material to reach fusion zone is lesser than Nickel interface material.

Corrosion Properties of Cu/Sn–3.0ag–0.5cu/Cu Solder Butt Joints Fabricated by Conventional Reflow and Microwave Hybrid Heating

Corrosion Properties of Cu/Sn–3.0ag–0.5cu/Cu Solder Butt Joints Fabricated by Conventional Reflow and Microwave Hybrid Heating

Filler powder free joining of SAF 2507 using selective microwave hybrid heating technique

Microwave Hybrid Heating (MHH) based joining of super duplex stainless steel (SAF 2507) with cross-sectionaldimensions 3.5 mm ×3 mm has been carried out for the first time by using a microwave applicator of 900 W operated at2.45 GHz for 400 s. Graphite rods have been used instead of traditionally used charcoal powder to serve as susceptormaterial. Graphite rods are good susceptor of microwave radiations therefore the presence of these rods helps in initiatingand carrying forward the joining process. Moreover, the melting temperature can be achieved for specimens underinvestigations through this novel process thereby eliminating the need of using any filler powder. Absence of filler powderreduces the process cost significantly. The joints have been mechanically characterized by Vickers micro-hardness andphysically characterized by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) tests. It hasbeen observed through these tests that micro-hardness of the joints was more than the base alloy due to transfer of carbonfrom graphite rods to the joint zone.

Application of graphite rods in producing Inconel 625 (UNS N06625) joints through the use of microwave radiation energy

Microwave energy is very efficiently being harnessed to join metallic materials these days. Although, use of microwaveenergy to join metallic materials is in its initial stage but, it has led to an outstanding development in the field of manufacturing. In this research work, joining of Inconel 625 (UNS N06625) without any filler material has been performed with the help of a novel process by harnessing microwave energy from a 900 W microwave applicator. Major novelty of thiswork is the application of graphite rods in accelerating the joining process based on the use of microwave radiation energydue to which it could become possible to join the Inconel specimens without using any filler powder. Selective microwave hybrid heating has been performed using six graphite rods and the process time taken for successful joining of Inconel625 specimens has been 360s. Three repetitions have been done using the mentioned process parameters. Mechanical characterization of the developed joints has been done with the help of Vickers micro-hardness tester and tensile testingmachine. The mean microhardness of the joints has been observed to be 325.1 HV at the joint region which came out to be 10.32 % more than that of the base alloy. The mean ultimate tensile strength has been observed to be 319.9 MPa with mean elongation of 5.3% which has been observed to be less than that of the base alloy.

Significance of fabrication parameters over the mechanical and metallurgical properties of AMMC joint formed by microwave hybrid heating

Purpose The purpose of the study is to fabricate a joint between two aluminium metal matrix composites using microwave hybrid heating (MHH). Design/methodology/approach Taguchi design of experiments was applied to conduct the experimental study. The mechanical properties such as ultimate tensile strength, micro-hardness and porosity were studied. Grey Relational Analysis was applied to understand the significance of fabrication parameters of best performing sample. The dominant factor of fabrication was analysed using ANOVA. The best performance sample was further characterised using X-ray diffraction and field emission scanning electron microscopy. Energy dispersive X-ray was used to analyse the elemental composition of the sample. Findings The Aluminium Metal Matrix Composite (AMMC) joint was successfully fabricated using MHH. The mechanical properties were mainly influenced by the fabrication factor of exposure time. Originality/value The formation of AMMC joint using MHH might explore the way for the industries in the field of joining.

Optimization of microwave processing parameters on powder-metallurgical 316L stainless steels

ABSTRACT Ultra-rapid microwave sintering of powder metals is recognized for better process advantages, namely less process time, uniform volumetric heating, and fine microstructural features that will improve mechanical and corrosion properties. In the present study, austenitic (316 L) stainless steel powder compacts were sintered using a multimode microwave hybrid heating system at solidus (1200°C and 1250°C) and super-solidus (1300°C) temperature with different holding times 30, 45 and 60 min. Mechanical as well as electrochemical responses were correlated with the microstructural features and densification characteristics. The samples sintered at 1300°C for 60 min have shown improved densification and higher tensile strength of 474.3 MPa with 22.1% ductility. It is also noted that an increase in sintering temperature resulted in excellent corrosion resistance in the order of ten times. The input process parameters and the output property responses are mathematically modeled with the help of RSM. The developed equations and experimental studies are in good agreement with output responses (sintered density, yield strength, %elongation, microhardness, corrosion rate) with 0.92 to 0.95 desirability. The validation of optimized output responses is evaluated by conducting confirmation tests at two conditions (1300°C for 60 min & 1300°C for 52 min) and are in line with regression model analysis.

Microwave sintering response of different grade stainless steels and its influence on metallurgical properties

ABSTRACT Ultra-rapid microwave sintering of powder metals will provide fine microstructural features that improve mechanical properties. In present study, three grades of stainless steel powder compacts (316L, 430L, 410) were produced using a uniaxial compaction unit. These compacts were sintered by microwave hybrid heating method at 1300°C (super-solidus region). The densification response, microstructural attributes, and mechanical properties were compared at 30, 45 and 60 min holding times. The compositional analysis was performed with the help of optical emission spectroscopy (OES) and scanning electron microscopy equipped with energy dispersed spectroscopy(SEM-EDS). The results obtained from both spectroscopies are compared for the sintered samples. The correlation of mechanical properties is analysed with evolved microstructural attributes (pore volume, pore shape and pore distribution). The excellent strength of 457 ± 16 MPa, 466 ± 6 MPa and 476 ± 26 MPa with 23 ± 1.3%, 14 ± 1.5% and 11 ± 1% of ductility is observed for sintered AISI 316L, 430L and 410, respectively.

Joining of dissimilar metals by microwave hybrid heating: 3D numerical simulation and experiment

The potential of microwave heating for joining of dissimilar metals is not much explored. This work is a unique investigation on finite element method (FEM) simulation of joining oxygen free copper (OFC) to stainless steel (SS304) using microwave energy. Cu powder of size 4 μm was used as an interlayer for the simulation which is followed by experimental study. COMSOL Multiphysics 5.3a was used to simulate the joining of dissimilar metals by microwave heating and to achieve the temperature reading across the joint cross-section. The temperature of ∼966 °C was observed at the joint interlayer/interface and ∼1062 °C at the graphite susceptor for the microwave exposure time of 14 min. The temperature of the susceptor were measured experimentally in a time interval of 60 s and was observed to be in agreement with the simulated results. The microstructure of the joint samples processed between 12 and 14 min of microwave exposure time was analysed. The microstructure analysis of joint depicted that, the porosity at the interlayer decreases with increase in microwave exposure time.

Effect of Susceptors on Joining of AA6061-T6 to AZ31B by Microwave Hybrid Heating

Effect of Susceptors on Joining of AA6061-T6 to AZ31B by Microwave Hybrid Heating

In situ surface modification of stainless steel with hydroxyapatite using microwave heating

The present work involves enhancing the biocompatibility of austenitic stainless steel (SS-316L) implants by changing its surface composition and morphology through the microwave hybrid heating (MHH) technique. The polished SS-316L alloy surface layer was modified with bioactive hydroxyapatite (HAP) powder by utilizing an Industrial microwave oven operated at 2.45 GHz and 1.1 kW. The modified layer of SS-316L alloy was characterized in terms of phase analysis, microstructure investigation, porosity analysis and apatite forming ability. The microstructural investigation revealed that the presence of austenite dendrites with HAP along with some reaction induced phases like Fe3P, FeP, and Fe2P mainly in the inter-dendritic regions of the modified layer of SS-316L alloy. The microhardness of modified layer was higher than that of the unmodified layer of SS-316L alloy. The modified layer exhibited porosity in the range of 2% to 3%. The in-vitro study performed in simulated body fluid (SBF) solution indicates that the microwave-assisted surface modified layer of SS-316L alloy exhibited an improved bioactivity. The SEM images indicate the formation of apatite layer in the modified layer of SS-316L alloy. The observed biological improvements in the microwave-assisted modified layer was due to the cladding induced changes in the surface morphology and surface chemistry of the SS-316L substrate material.

Densification kinetics of P/M austenitic (316L) stainless steels processed by rapid microwave hybrid heating method at various conditions

ABSTRACT Microwave sintering of powder metals is recognised for better process advantages, namely, less process time, rapid densification, uniform volumetric and selective heating characteristics. There are certain theoretical analyses to explain the mass transport mechanisms during microwave sintering. The current study reports on an investigation of densification kinetics in austenitic (316 L) stainless steel powder compacts processed by microwave hybrid heating method at solidus and super-solidus temperatures. The analysis of densification kinetics and sintering mechanisms were studied using the grain growth exponential and time-temperature plots. The results revealed that the major densification is achieved through bulk diffusion (viscous mass flow) at a higher temperature (1250°C–1300°C) under the super-solidus region while grain boundary retardation is the mechanism for the reduced grain growth at a lower sintering temperature (1100°C–1200°C) under solidus region. The apparent activation energies are calculated using the Arrhenius plot and classical grain growth analysis simultaneously. The activation energies of 42 ± 3 kJ/mol and 24 ± 2 kJ/mol are observed for the samples sintered at a lower temperature. The higher activation energies of 219 ± 8 kJ/mol and 254 ± 7 kJ/mol are obtained for the samples sintered at 1250°C–1300°C for both analyses.