Hybrid Microwave Research Articles

Joining and characterization of SS-430 using microwave hybrid heating technique

Purpose The purpose of this paper is to based upon the joining and characterization (mechanical and metallurgical) of ferritic stainless steel (SS)-430 using a microwave hybrid heating (MHH) phenomenon. Design/methodology/approach The preliminary experiments were conducted using nickel-based powder as interface material using a domestic microwave oven at a frequency of 2.45 GHz and 900 W power for 720 s. The processed joint was metallurgically characterized by means of X-ray diffraction, Energy-dispersive X-ray spectroscopy and Field emission scanning electron microscopy. Mechanical characterization was done by means of tensile and Vickers’ microhardness testing to check the hardness and strength of the joint. Findings The metallurgical study revealed that the microstructure and formation of numerous phases of Fe2Si3 accompanied by chromium and nickel carbides. The average hardness of 359 Hv at the center of the joint and 637 Hv around the boundaries of the joint was observed. The tensile strength of the joint was observed to 471 MPa with an elongation of 9.02%. The worn surface of the joint signifies the presence of plastic deformation and it was limited due to the presence of harder phases such as Ni3Si and Ni3C. Research limitations/implications The concept of microwave joining of metals is a very challenging task as the temperature can not be controlled in the inert atmosphere of the microwave. It has been also observed that at certain elevated temperatures, the material starts absorbing the microwaves; which is unknown. So, a more intensive study is required to overcome these kinds of limitations. Practical implications MHH technique can be used to process different materials such as ceramics, composites and polymers. SS-430 joined by microwave heating is highly corrosion resistive and has wide applications in refrigerators cabinet panels, dishwasher linings, chimney liners, lashing wires, etc. Originality/value As of the author’s best knowledge, no work has been reported on the joining of SS-430 which has huge potential in the industries. Also, no work has been reported on the characterization of microwave joined SS-430.

Experimental investigation on characterization of microwave welded Al6061-Gr-SiC hybrid metal matrix composites

In the present work, experimental microwave welding of Al6061-6%Gr-SiC hybrid metal matrix composites (MMC) in bulk form has been carried out. The principle of microwave hybrid heating was applied with domestic microwave having the frequency of 2.45GHz and 900W power. The interface powder Al6061 and susceptor as charcoal powder were used for the welding process. The stir casting process was used to prepare Al6061-6%Gr-SiC hybrid MMCs by varying SiC content by 3%, 6% and 9% and keeping 6% graphite constant by wt%. The composite weld joints were characterized by scanning electron microscope (SEM) equipped with energy dispersive spectrum (EDS) and mechanically through tensile test, Rockwell hardness test and impact test. The microstructure study showed the good metallurgical bonding between the interface and base composites without any visible cracks. The SEM-EDS study revealed the formation of various carbides and inter metallics at the weld interface. The average ultimate tensile strength of the joint was found to be 135MPa with 4.3% elongation. The average Rockwell hardness at the weld joint observed was 61.5HRB. The average impact strength of welded composite was 1.62J/mm2.

Harmonic Dual-Band Diode Mixer for the X- and K-Bands

This paper presents a new dual-band diode mixer for the X- and K-bands. The proposed mixer consists of a pair of series-connected diodes and a frequency-dependent delay line that operates at 180° and 360° at the X-band of 10.525 GHz and at the K-band of 24.15 GHz, respectively. Without reconfigurable devices such as switches, the proposed mixer operates as a single-balanced diode mixer at the X-band and a subharmonically pumped antiparallel diode mixer at the K-band simultaneously. The designed circuit was implemented in a hybrid microwave integrated circuit using discretely packaged RF components on a microwave printed circuit board. The measurement results showed conversion losses of 6.5 dB and 16.6 dB at the X- and K-bands, respectively.

Experimental demonstration of a microwave photonic link using an optically phased antenna array for a millimeter wave band.

We present a hybrid radiofrequency and microwave photonic link at 25 GHz using the chromatic dispersion of an optical fiber to steer the beam of a three-element planar dipole-based phased antenna array (PAA). Our team has designed and developed an in-house built PAA, experimentally verified its parameters, and successfully demonstrated optically controlled beam steering as measured in an anechoic chamber. Moreover, a detailed analysis of the optically based beam steering in the proposed microwave photonics system has been carried out, with data transmission achieving an error vector magnitude as low as 5.6% for the frequency of 25 GHz and 20 MHz bandwidth.

Development of Microwave Hybrid Heating Welded Joints of Inconel-600 Superalloys using Grey Relational Analysis

Inconel-600 superalloys have a number of applications in space and aerospace sector due to its unique characteristics of high strength at elevated temperature, low weight, corrosion resistance and high wear resistance. However, due to these characteristics, Inconel-600 superalloy poses challenges in joining. Therefore, an attempt has been made to resolve these issues using microwave hybrid heating (MHH). The characteristics of the constituents of MHH process have large impact on the welded joint’s strength. This paper examines the impact of control parameters on the ultimate tensile strength (UTS) and percentage elongation (EL) of Inconel-600 plates, which are welded via MHH. Design of experiments was carried out in accordance with Taguchi L16 orthogonal array (OA), taking in consideration of filler powder particle size (FPS), susceptor and separator. Multi-performance features were optimized via the effective utilization of Taguchi-based grey relational analysis (GRA) approach. ANOVA results show that the predominating factor to govern the joint strength is FPS followed by the susceptor and separator. The validation experiments are performed on the predicted optimized setting of process parameters. First level of FPS (30μm), second level of susceptor (Graphite) and second level of separator (SiC) were found as the optimized parametric settings.

A Comparative Studyon Characteristics of Inconel-625 Joints Developed through Microwave Hybrid Heating and Tungsten Inert Gas Welding

In recent years, microwave welding has received attention for joining of similar and dissimilar metals due to its major advantages like volumetric heating, selective heating of target materials, energy saving and sustainability. In the present work, the microstructural characteristics and mechanical properties of Inconel-625-welded joints developed through microwave hybrid heating and those produced by TIG welding have been compared. Welding through microwave hybrid heating (MHH) was carried out using Inconel-625 interface filler powder of 50 μm size, while TIG welding was carried out using ERNiCrMo-3 filler wire of 2.5 mm diameter which had a composition similar to that of Inconel-625 alloy. The welded samples were characterized in terms of microstructural observations and tensile and microhardness properties. The study reveals that the joining of bulk metals through MHH has potential in manufacturing industries in the near future. TIG-welded joints exhibit superior strength compared to MHH joints because of fine grain structure, lower amount of segregation in the weld zone and also smaller width of the weld zone in joints developed through MHH. The hardness in the weld zone of welded joints in both the cases is observed to be almost the same. Use of a finer interface filler of 20–25 μm particle size may further contribute to improving the mechanical properties of the joints developed through MHH. Furthermore, the use of industrial microwave furnace may improve the strength of MHH-welded joints as the process may be integrated with real-time temperature measurement of the joint zone so as to achieve better control over the process.

Microwave hybrid fast sintering of red clay ceramics

AbstractThis work aimed to examine the performance of the hybrid sintering of clay ceramic in a microwave furnace, compared to the sintering process in a conventional furnace. The raw materials were subjected to X‐ray fluorescence, loss on ignition (LOI), X‐ray diffraction, particle size distribution, real specific mass, and thermogravimetric analyses. The red clay ceramic mass was prepared, extruded, pre‐sintered in a conventional furnace at 600°C/60 min, and sintered at temperatures between 700 °C and 1100 °C. The sintering conventional (resistive oven) was carried out for 60 min with a heating rate of 10°C/min. In the microwave furnace, the sintering times were 5, 10, and 15 min, with a heating rate of 50°C/min, with a sintering chamber coated with silicon carbide (susceptor). The sintered specimens were characterized according to linear shrinkage, water absorption, apparent porosity, apparent specific mass, X‐ray diffraction, Raman spectroscopy analysis, spectroscopy analysis in the ultraviolet and visible regions, microhardness, and scanning electron microscopy. The results showed that microwave sintering promoted an increase in the microhardness and apparent specific mass, and reduction in water absorption and apparent porosity values, due to greater densification in the microstructure. The best results occurred for specimens sintered at 1100°C.

Wear behavior of microwave-processed Ni-WC8Co-based functionally graded materials

Functionally graded materials are inhomogeneous materials with the gradual change in properties with position. In this research work, functionally graded clad layers of Ni-WC8Co-based materials with varying compositions of WC8Co from 0 to 30 wt% were processed using a cost-effective and energy-efficient microwave hybrid heating technique. Single-layer clads of compositions corresponding to different functionally graded clad layers were also developed through microwave heating for comparing different properties. The processed functionally graded clads were characterized through microstructural analysis (scanning electron microscopy/energy-dispersive X-ray spectroscopy) and Vicker’s microhardness quantification. Microstructure results showed the functionally graded clad of approximately 2 mm thickness was free from any visible pores and interfacial cracks. Microwave heating resulted in the formation of hard phases in the functionally graded clad layers, and these layers exhibited significantly higher microhardness values. Further, the tribological performance of developed functionally graded clad was examined under dry sliding conditions using pin-on-disk-type tribometer. The influence of varying sliding velocities and sliding distances on the wear characteristics of microwave-processed functionally graded clads were investigated. It was observed that microwave-processed functionally graded clad exhibited approximately 95%, and 29% higher wear resistance than the SS-304 substrate and Ni + 30%WC8Co-based single-layer clad respectively owing to its better mechanical properties.

Hybrid Microwave Medical Imaging Approach Combining Quantitative and Qualitative Algorithms

This letter proposes a hybrid microwave medical imaging (MMI) approach to reconstruct the inner structure of the human body with improved accuracy on mapping the dielectric permittivities. Specifically, the results of the quantitative and qualitative MMI are employed to act as the a priori information for each other through an iterative process. Hence, the hybrid MMI approach combines the advantages from both the quantitative and qualitative algorithms to visualize simultaneously the inner body structure with clear tissue boundaries and the positions of strong scatterers. This proposed approach is evaluated by considering the medical scenario of bone fracture detection. The resultant image shows that the relative error of the reconstructed permittivity can drop by 33% for the scanned body area when compared to the one generated by the conventional quantitative MMI, whereas the position of a bone fracture can still be precisely indicated.

Slurry Erosion Resistance of Microwave Derived Ni-SiC Composite Claddings

Hydro machinery components such as turbines, pipes, guide vanes, and pumps suffer from severe slurry erosion caused by the abrasive particles entrained in working fluid. In the current work, an array of systematic slurry erosion tests were executed to study the influence of impact angle on slurry erosion rates of Ni-SiC based composite claddings developed on SS 316 L through microwave hybrid heating. Various microstructural and mechanical characterizations such as micro and nano-indentation, x-ray diffraction (XRD), and scanning electron microscopy (SEM) were performed on the developed claddings. The claddings contain 5 wt.% of SiC particles of different size fractions from nano to micro (unimodal) and combination of both in the matrix (bimodal). Slurry erosion studies were performed on the developed claddings at different impingement angles. The claddings exhibited good metallurgical bonding with the substrate without any pores throughout. The developed claddings exhibited high hardness and elastic modulus compared to the substrate material. A significant improvement in the erosion resistance of the claddings was observed with the addition of bimodal sized SiC secondary particles. The enhanced erosion resistance of the claddings could be attributed to the higher fracture toughness and hardness of the developed coating. Among the developed coatings, the bimodal sample with 5% SiC claddings showed at least two times better erosion resistance than hydro-turbine steel at almost all the impact angles. SEM studies performed on the eroded samples showed micro-cutting and plowing as the main modes of material removal at lower impact angles.

Development of novel experimental procedure for microwave hybrid heating based joining using graphite rods

In this study, iron based alloy specimens have been joined successfully through microwave hybrid heating with a novel procedure of using graphite rods as susceptor. Specimens having 3.5 mm × 3 mm cross-section were selected for butt joining. Microwave applicator used for the joining worked at 2.45 GHz frequency and 900 W. Graphite rods were employed as the susceptor medium. Susceptor medium increases the temperature of alloy which leads to coupling of microwaves. Optimum time for obtaining the joints of iron based alloy has been found by trial method. After the successful joint formation, micro-hardness testing was also done. Hardness of the joint is found to be more than the base alloy.

Investigation and characterization of brass joint fabricated by microwave hybrid heating process

Microwave energy is a novel technique for joining metals and composites in the field of manufacturing. In this paper, joining of bulk metallic material (Brass) is successfully carried out using microwave hybrid heating. Joint is formed at 480 sec exposure time with power 900 W and frequency 2.45 GHz. The joint is studied by using microstructural analysis, XRD, SEM, Tensile strength, Hardness and % elongation. Microstructural analysis reveals that small amount of porosity is observed and joint is clearly visible. Formations of various compounds which improve the mechanical properties of the joint are shown in XRD analysis. SEM analysis indicates the formation of dense joint with no cracks and voids. Tensile strength, hardness and percentage elongation were measured i.e. 292.67 MPa, 50 Hv and 7.30% respectively.

A systematic review on recent progress in advanced joining techniques of the lightweight materials

We are living in a time where the emphasis is given on the development of new and improved materials having high strength and are correspondingly light in weight for application in fields such as transportation, aerospace, medical and other such related areas. These new materials developed need to be processed and joined with oneself and other materials as well. The paper presents a brief understanding of the advanced joining processes namely friction stir welding, microwave hybrid heating, electron beam welding, laser beam welding, thermo-hydrogenated diffusion bonding, electromagnetic welding and ultra sonic welding. The purpose of these advanced joining techniques is to increase the efficiency of the joining process and prevent failure. The objective of this review paper is to provide an insight into the principles, current trends and research gaps in advanced joining techniques.

Application of microwave in welding of metallic materials – A review

Abstract The application of microwave in the processing of metallic material is relatively a new development in this area. The microwave energy is applied in various fields of engineering for processing of metallic materials in the form of cladding, sintering, casting and welding etc. Microwave welding is an advanced method of joining of materials, but still the investigators have utilized this technique for the joining of limited materials only. The inherent advantages associated with the microwave processed products are due to its hybrid heating phenomenon, which consumes lesser energy and time. The MHH results in uniform heating of the material. The uniform heating reduces the thermal gradient inside the weldment; which caused the reduced thermal stresses in the joint. The present paper outlines the basic characteristics and principles of microwave hybrid heating (MHH) technique used for joining of metallic materials. In addition to this, the paper reveals discussions about joining of different types of materials using MHH technique, their interfacing layer characteristics, exposure time, metallurgical and mechanical properties etc.

Joining of dissimilar metals using microwave hybrid heating and Tungsten Inert Gas welding - A review

In the new era of the Industrial Revolution, a new method is established in the welding of similar/dissimilar metals. Welding of dissimilar metals still possesses a significant challenge because of their incompatible material properties and structure. Using new materials in automobiles, aerospace has made dissimilar metal welding a very essential part of industrial application. Microwave Hybrid Heating (MHH) is a technique that has acquired a lot of attention in the recent years because of its precise and controlled heating and it can help in selective heating of materials. This process can join many materials and is also cost-effective and environment friendly. This paper reviews the successful joining of dissimilar metals through two non-conventional welding techniques namely Microwave hybrid heating and Tungsten Inert Gas welding but mainly focusing on the recent Microwave hybrid heating process with regards to the materials, susceptor medium, exposure time and the various techniques used for characterization of the joints. It can be concluded from the findings that limited study has been carried out in the field of dissimilar welding of metals through the above processes, especially microwave through microwave hybrid heating and there is scope for improvement and research.

Experimental study on microwave Ex-situ casting of AA 6061

Abstract Microwave processing of a metallic material melting and casting is a newly developed method. The irradiation of metallic specimen takes place inside the cavity of microwave applicator and it’s heated and melted due to microwave hybrid heating. In the present work, melting of AA 6061 established inside a commercial grade microwave oven with 1 kW power and 2.45 GHz frequency in ambient environmental condition. In this process pouring and solidification carried outside the applicator. The casket design and susceptor material properties influence on the microwave heating of specimen and hence melting of the charge. The interaction of microwave with specimen and its effect of heating and melting was observed in the present study. The developed specimen was characterized to check the cast quality. Microstructure study shows the homogenous grain structure with average grain diameter 3.25 µm. The average micro indentation hardness of the casts was found 89 HV.

Microwave hybrid heating based optimized joining of SS304/SS316

ABSTRACT In this study, the microwave hybrid heating process has been exploited to produce optimized joints of SS304/SS316. Three input parameters: materials of the specimens to be joined (X), grain-size of filler powder (Y), and processing time (Z) have been investigated to see their effects on two major joint properties: micro-hardness (P) and micro-tensile strength (Q). Welded joints of specimens have gone through mechanical characterization via Vicker’s micro-hardness tests and also the micro-tensile strength examinations. Outcomes have been used further for finding optimal settings of input parameters to achieve the best mechanical properties of joints. Grain-size of filler material is the most significant parameter; followed by specimen material. On the other hand, process time has little influence on output parameters within the small incremental time range of only 60 s considered during this work. SS304-SS304 (X1) specimen materials with 70 nm (Y1) filler powder at 360 s (Z1) processing time input settings help in achieving optimal micro-hardness (Poptimal) and micro-tensile strength (Qoptimal). Microstructure test results of the developed joints reveal the formation of dense metallic microstructures across the joining region which justifies the reason for higher micro-hardness and micro-tensile strength of the joint region.

Study of tribological properties on aluminium based hybrid composite developed through microwave energy

Abstract Aluminium alloy 6061 is used as a matrix material and reinforced with alumina and molybdenum disulfide by microwave sintering method. The conventional sintering technique has taken many years as of now and which also has several limitations like time and power-consuming. Microwave processing techniques are in the recent use of attraction to resolve the limitation of conventional techniques. In the current work Al6061 hybrid metal matrix composite reinforced with alumina and molybdenum disulfide (Al + 4% of Al2O3 + 2% of MoS2) was developed through a domestic microwave oven. The microstructural study reveals the consistent distribution of Al2O3 and MoS2 reinforcement in the microwave developed composite material and very minute porosity was observed in the developed structure. Microwave processed composites shown higher wear resistance than the aluminium alloy.The wear rate of the Al matrix is more compared to that of the developed microwave hybrid metal matrix composite with a composition of Al + 4% Al2O3 + 2% MoS2. The Addition of Al2O3 and MoS2 reinforcement might have resulted in the improvement of wear resistance of the developed material. Plastic deformation and formation of oxide on the surfaces at elevated temperature were observed on the developed microwave composite, which further allows for easy sliding over the surface of the disc surface and reduction of wear loss at faster speeds.

Challenges in joining of metallic pipes using microwave hybrid heating

Microwave hybrid heating (MHH) is a distinct and emerging alternative joining technique used to join metallic materials compared to available conventional joining processes such as FW, TIG, MIG, etc. MHH shows significant characteristics such as selective and volumetric heating, lower processing time, eco-friendly processing against conventional joining. This paper aims to investigate the joining of 316L stainless steel pipes by incorporating micrometric size (45μm) of 316L stainless steel powder in between the faying surfaces of the candidate material. Charcoal as a susceptor material was placed at the joint zone and exposed to microwave energy at 2.45 GHz inside the domestic microwave applicator at 900 W power levels. The challenges and principles involved in joining SS 316 L pipes using MHH have been discussed and initial experimental observations have been analyzed.

Influence of post clad heat treatment on microstructure and slurry erosion characteristics of Ni-based microwave clad

In this study, effect of high temperature heat treatment on microstructure and erosive wear performance of Ni-based clad was investigated. The clad was developed on a hydroturbine steel (CA6NM) substrate using microwave hybrid technique. The as-clad microstructure comprised of rod-like Cr enriched M7C3 carbides in γ-(Ni, Fe) solid solution. Post clad heat treatment at 750 °C led to M7C3→M23C6 transformation accompanied by increase in carbide volume fraction. On the other hand, heat treatment at 1000 °C clad resulted in partial dissolution of the eutectic carbides. Among the tested samples, 750 °C heat treated sample exhibited higher erosion resistance. The erosive wear behaviour of Ni-based clad, before and after heat treatment, showed good correlation with hardness (at 30°) and elastoplasticity (at 90°).