During polarization, short range displacement of charge is involved; while long range transportation of charge occurs during conduction. Movement of ions through the material and their collisions with other species result in Ohmic losses, which further lead to ionic conduction losses. An increase in frequency reduces the time required for transport in the field direction, which further results in decreased ionic conduction [7].

In this paper, various research developments in different sub-disciplines of Microwave joining technique are reviewed. These include specimen, interfacing materials, types of susceptor used, various experimental setup adopted. Review paper of microwave joining of metals has not been presented yet. After reviewing the research developments, paper proceeds towards research gaps and future scope of Microwave joining.

2. Research Developments in Microwave joining:

After reviewing literature, various developments related to microwave joining of metals and alloys have been categorized into four types:

· Specimen based developments,

· Types of susceptors,

· Types of interface powder,

· Experimental set-up based developments

These are briefly discussed in following sub-sections.

2.1 Specimen Based Developments:

Different types of specimen ranging from thin sheets to bulk metallic materials have been joined using microwave joining process. Dimensions and geometry of the cross-section are the parameters which play a significant role in MHH based joining. This is because, time required for melting and joining depends a lot upon these parameters. Joining of rectangular as well as circular cross-sections of different sizes has been investigated by many researchers. Siores and Rego [8] achieved successful joining of thin metallic material with rectangular cross-section having thickness in the range of 0.1 mm to 0.3 mm using magnetron of 2 kW power. Arcing was observed at the interface of two specimens butt against each other with small gap in between the mating surfaces during joining process. Arcing leads to melting of the mating surfaces which were then forced against each other under externally applied pressure in order to create the joint.

Copper is one of the most difficult-to-weld materials using conventional mode of joining. A new approach was established to join copper in bulk form using microwave energy by Srinath et al. [9]. Trials were done using copper plates of length × width × thickness (15 × 12 × 4 mm³) as well as coins of 18 mm diameter and 12 mm thickness. Uniform microstructure was obtained which can be attributed due to volumetric heating of joint zone. It was found that there was a change in atomic structure of copper powder during microwave irradiation. Coupling of microwaves with metals improves due to presence of oxides during joining. The microwave interaction was favorable with smaller size metallic powder particles. The values of hardness and porosity were observed to be 787 Hv and 1.92 % respectively. Average ultimate tensile strength of joints was 164.4 MPa with 29.21 % elongation. Mode of failure of copper joint was found to be a combined effect of ductile and brittle failures.

Joining of aluminum alloy in bulk form was carried out by Singh et al. [10]. Specimens were used in the form of plates with dimension 35 × 12 × 5 mm³. Microstructure study, elemental analysis, micro-hardness survey and X-ray diffraction (XRD) were carried out for characterizing the joints. Exposure time of 600 s in microwave heating resulted in successful joint creation. Obtained value of hardness of joint was 72.410 Hv.

It is difficult to prepare a microwave joint of MS, SS, Inconel etc. specimens compare to aluminium because of their higher melting point. Joining of MS plates using microwave energy was successfully obtained by Bansal et al. [11]. Trials were done on MS plates with dimensions of 30 × 10 × 5 mm³ with gap of 0.3 mm between the two interfacing surfaces of substrates. Vicker’s micro-hardness of joints was 42030 Hv which was sufficiently higher than that of the base metal. Average tensile strength of 250 MPa and elongation 6 % were achieved.

Dwivedi et al. [12] worked on microwave joining of 1018 MS joints. Three input parameters (power, time and temperature) were used to identify their effect on desired output parameter (tensile strength) of the joint. The macrostructure and microstructure of the welded joints within the prescribed range of process parameters resulted in proper fusion of interface powder with the base material. They concluded that in confined range of process parameters, tensile strength showed an inverse relation with rated power output, while a direct relation with time of welding and temperature.

Bansal et al. [13] utilized MHH to produce butt joint of rectangular cross-section 10 x 4 mm² using Mild Steel (MS) plates of length 15 mm and 10 mm. Gap between the two specimens was kept at 0.4 mm. Joints were characterized using XRD, Scanning Electron Microscope (SEM), Electron Probe Micro Analysis (EPMA), Vickers’s micro-hardness tester, and Universal Testing Machine (UTM). XRD spectrum of joints showed the formation of substitutional type of solid solutions at interface region. Complete melting of powder particles was confirmed by SEM images of joints. Diffusion bonding happened between substrates and the powder particles. The obtained value of Vicker’s micro-hardness (42030 Hv) of joint was higher as compared to parent metal (23010 Hv). Tensile strength of specimens was 240 MPa. SEM micrographs of fractured samples revealed mixed mode of failure consisting of ductile and brittle modes.

In 2011, Srinath et al. [14] joined dissimilar specimen by microwave joining. Specimens of MS-SS316 with measurement of 25 mm × 12 mm × 6 mm were taken by them. At interface of both substrates, they placed a layer of Nickel based powder with particle size of 40 µm in slurry form. A successful metallurgical bond between dissimilar metals was achieved. Mechanical properties achieved after characterization of dissimilar joints were Vicker’s micro-hardness 133 Hv, ultimate tensile strength 346.6 MPa with an elongation of 13.58%. It was observed that both shearing of the brittle carbides and oxides and ductile matrix’s plastic flow phenomenon was responsible for fracture of dissimilar joints under tensile loading. The work was extended later, in 2014, by Bansal et al. [15] with different parameters. Bansal et al. [15] used smaller specimen of size 25 × 10 × 4 mm³ and SS-316 powder as interfacing material with particles size of 50 µm. They carried out the joining process at 1200 W power level as against 900 W power level used earlier by Srinath et al. [14]. In characterization of welded joints apart from XRD, field-emission SEM, micro-hardness and tensile testing, they also measured the temperature of heating zone with an in-built non-contact infrared pyrometer. Optimum temperature for joining was found to be 1360 ºC. Flexural strength of dissimilar welded joints was also measured. Dendritic type microstructure was revealed after microstructure examination of welded joints in fusion zone. Magnitude of 380 Hv of micro-hardness was found in the core of welded zone which was significantly higher than base material. Average ultimate tensile strength and flexural strength of welded joints were obtained as 420 MPa with an elongation of 6.67 % and 787.5 MPa with an elongation of 5.14 % respectively. The difference in the findings of Srinath et al. [14] and Bansal et al. [15] is attributed to difference in process parameters used during joining.

In 2013, Gupta et al. [6] studied the microwave joint formation of MS with Stainless Steel (SS) specimens with size 50 × 12 × 3 mm³. Joints were characterized for their microstructure, tensile strength, percent elongation, and micro-hardness. Characterization results revealed that very fine microstructure was obtained. Recorded values of ultimate tensile strength, percent elongation, and hardness were 340.16 MPa, 11.67 % and 130 Hv, respectively. Later, in 2014, Gupta et al. [16] also carried out SS-SS joint formation for specimen size 50 mm × 12 mm × 4 mm. Characterization results revealed effective fusion of metal and fine microstructure with clearly visible joint. Obtained values of micro-hardness, tensile strength and elongation was 145.3 Hv, 323.16 MPa and 11.30 %, respectively.

Characterization of joints of bulk SS-316 with dimensions 25 × 15 × 4 mm³ was performed by Bansal et al. [17]. From the characterization it was inferred that epitaxial growth near fusion zone and equiaxed microstructure in joint zone were observed. Grain boundaries were flooded and precipitated with carbide of Cr. Due to presence of hard carbides at grain boundaries, Vicker’s micro-hardness achieved was significantly higher than that present in the fusion zone. The measured ultimate tensile strength of joint was 425 MPa with an elongation of 9.44 %. Tensile testing revealed that constraint for higher rate of plastic deformation was due to presence of intermetallics, metallic carbides and joints get failed due to ductile fracture in material.

Srinath et al. [18] also achieved joining of austenitic SS (SS-316) using microwave energy method. Specimens with measurement of 25 mm × 12 mm × 6 mm were taken for joint development. Almost complete metallurgical fusion in joint area was observed. Grain growth at core of the joint was equiaxed and development of grains at interface was columnar. Characterization of joints was done through field- emission SEM, XRD, micro-hardness and tensile strength tests. The average micro-hardness was found to be 29014 Hv at core of the joint. However, significantly higher hardness was observed to be 42015 Hv in the interface zone. Ultimate tensile strength of joints was 309 MPa with 11.50 % elongation.

Successful joining of Inconel 718 with SS-316L was also achieved by Bansal et al. [19] using MHH. Plates of size 25 mm × 10 mm × 4 mm of Inconel-718 and SS-316L were used in that work. The plates were kept in butt configuration with a gap of 0.5 mm. The average micro-hardness, ultimate tensile strength and elongation were identified to be 2305 Hv, 517.5 MPa and 18.18 % respectively.

Application of EM energy successfully used to join Inconel 718 plates by Bansal et al. [20]. Experiments with measurement of 15 × 10 × 4 mm³ of Inconel 718 plates were done. 0.2 mm thick layer of Nickel powder of average particles size of 40 µm was placed between interfacing surfaces of specimens. XRD, SEM, EPMA techniques were used for the characterization of welded joints. They concluded that MHH technique can be effectively used for melting of interlayer powder particles which results in metallurgical bonding with faying interfaces. The recorded ultimate tensile strength of welded joints was 400 MPa with an elongation of about 6 % using UTM. Fractography of failed welded joints showed ductile nature of failure.

Microwave joining of Inconel-625 of size 51 mm × 12 mm × 6 mm was investigated by Badiger et al. [21]. Micro-hardness recorded at the joint interface was found to be even higher than that of the joint zone. The measured average micro-hardness of joint zone was 35010 Hv. Tensile strength of the joints was 326 MPa with 9.04 % elongation.

Structure and property correlations for microwave based joints of Inconel-718 were obtained using alloy plates of size 30 × 10 × 4 mm³by Bansal et al. [22]. They concluded that mechanical properties of materials can be enhanced using post-weld heat treatment process by precipitation of strengthening phases in matrix. They also proposed that post-weld aging treatment instead of fully heat-treated conditions (solution treated and aged) can be effectively used to strengthen the weld.

Investigation on microstructure and micro-hardness of EN-31 microwave welded joints of size 125 mm × 22 mm × 0.6 mm with 0.5 mm width of interface material were fabricated by Rana et al. [23]. They carried out a comparative analysis of microwave joining, oxyacetylene gas welding and tungsten inert gas (TIG) welding. Width of weld bead, porosity and hardness of the joint were taken as performance measures for comparison purpose. Width of weld bead was lesser in microwave joining in contrast with oxy-acetylene and TIG welding. Value of volatization of carbon and ferrous particles was also lesser in microwave based joints which further reduced the chances of porosity. Maximum hardness was achieved in microwave joining technique.

Bagha et al. [24] performed comparative analysis of microwave joints of SS304 specimens with different interfacing materials. They used two interfacing powders for comparison; one was EWAC (Tungsten carbide bearing alloy) Nickel based powder and the other was 99.9 % pure Nickel based powder. Hardness of 99.9 % pure Nickel powder based joint (42.67 HRC) was found to be higher than that of EWAC Nickel powder based joint (30 HRC).

Recently, Bagha et al. [25] investigated the effects of powder size of interface material on selective hybrid carbon microwave joining of SS304 specimens. Workpieces for experiments as per ASTM designation E8/E8-09 standard with length of 40 mm, thickness 5 mm and width 3 mm were taken by them. Hardness results received after testing of welded joints revealed linear incremental from heat affected zone to bead centre. Harder welding beads and better tensile strength can be obtained using smaller grain size of Nickel powder. However it results in decreased ductility of the joint.

Research work discussed earlier is related to joining specimens of rectangular cross-section only. However, circular cross-sections have also been investigated by Saxena et al. [26] for joining of bulk copper pipes with outer diameter 10 mm and wall thickness 1.6 mm. They also studied the effects of different process parameters such as time, positioning of work piece in applicators cavity, length of specimens, thickness of slurry, and type of susceptor material on joint formation. The study was helpful in evaluating optimum position of work-piece which was observed to be 16 mm in height at the centre of base plate for maximizing the intensity of incident microwave energy. It was noticed that the length of specimen restricted to 10 mm because there was no melting above this limit and the average length of 8 mm was taken during experiments.

2.2 Susceptors Based Developments:

Microwave joining of metallic materials is mostly performed using some form of susceptor material. However it does not mean that susceptor-less joining is not possible. MHH technique has been widely used by many researchers for joining of metallic materials [5], [6], [9–26]. MHH can be achieved using two alternative methods viz., use of separate heat source such as electric furnace in combination with microwaves; and; using external susceptor that efficiently couples with the microwaves. In latter method, susceptor is used as microwaves absorbing material. When microwaves incident on susceptor, its temperature increases beyond its melting temperature results in transfers of heat to metallic material in conventional mode. After gaining heat the temperature of metals increased up to some critical value (T_c). After reaching at critical temperature, they start direct coupling with microwaves.

Apart from initiate the coupling of microwaves with metals and alloys, susceptor can also used to make limit for the liquefied interlayer as it doesn't permit diffused metal to flow out from the joint area. MHH technique seems to have critical potential to use microwave energy where it is required to heat a target zone without heating entire material. Generally charcoal powder is used as a susceptor medium and to concentrate the microwaves for localized heating. It is easily available, soft and of lesser cost. Placement of susceptor is very important to ensure selective heating in joining zone. It is a good practice to place a susceptor as near as possible to joint area. Some researchers have also investigated the use of susceptors other than charcoal as discussed next.

Silicon carbide (SiC) powder was used by Singh et al.[10] To initiate direct coupling of microwaves with metals by increasing their temperature up to a critical value. It was also used to provide prevention of direct contact of microwaves with metals and alloys. Bansal et al. [15] used SiC as a susceptor in powder form. They also used SiC substrate of size 25 × 25 × 10 mm³ as susceptor during another research [17].

Saxena et al. [26] performed comparative analysis of three different susceptors, i.e., wooden charcoal, stone charcoal and graphite powder during joining of copper pipes. Melting point was not reached even after 12-15 minutes; moreover; red hot condition was also not observed while working with stone charcoal. In case of wooden charcoal, after 10-12 minutes, melting point was observed. For graphite powder, red hot state and melting point state were observed quickly as compared to other two susceptor mediums. Corresponding states were achieved in 2-3 minutes and approx. 6 minutes respectively. Using graphite powder with approx. 5-6 gm and exposure time of 420-540 sec., no arching, rapid burning, concentrated heating and melting was observed during experiments. Thus graphite powder was found to be the best performing susceptor material among the three materials.

2.3 Interface Powders Based Developments:

Materials with good absorbing characteristics and ability to efficiently convert microwave energy into heat can be directly heated and joined. But low dielectric loss materials such as metals require the use of an interface material during microwave joining. Most of the researchers used Nickel based powder at interface between the joints. Interfacing slurry which consists of interfacing powder and an epoxy resin (Bisphenol–A, Blumer 1450XX) is used as bonding agent. Epoxy resin helps in binding the interface powder particles together and thus helps in producing a smooth joint. Thin layer of slurry is formed at the interfacing gap. Increase in temperature of the joint zone results in evaporation of the epoxy resin and the interfacing gap is filled with molten interfacing powder particles. Various interfacing material was used during experiments by researchers. Out of all bonding material Nickel based powder (EWAC) has better capability of coupling with SS and has good weldability [17]. Researchers concluded that joining of MS and SS, SS-SS can be done using 95% Nickel based powder and 5% epoxy resin which formed good joint.

Proportion of interfacing powder and blumer also plays a significant role in producing good joints in microwave joining. Optimal ratio of Nickel powder and blumer was experimentally evaluated by Bagha et al. [25]. Best joints were obtained when ratio of Nickel powder and blumer was set at 75:25 during joining of SS304 specimens.

Comparative studies of effect of different sizes of pure Nickel powder on joint properties were carried out by Bagha et al. [25]. Homogeneity and Nickel powder particle size showed inverse relation. Hardness and ultimate tensile strength obtained after characterization was higher for lowest powder particle size.

Many researchers have used interface powder other than pure Nickel. Copper powder with 99.5% purity and approximate particle size of 5 µm was used as sandwich layer by Srinath et al. [9] to obtained joining of copper in bulk form. XRD pattern revealed transformation of some copper powder particles into copper oxides. XRD results demonstrate that preferential orientation (1 1 1) was obtained after transformation from dominant orientation (3 1 1) which was initially present in copper powder during microwave processing.

Copper in powder form with 99.5% purity and particle size of 5 µm was used as an interfacing layer by Sexena et al. [26] to join bulk copper pipes using MHH technique. Homogenous heating produced through metallic powder in the joint zone during microwave irradiation resulted in fusion of powder particles and bulk metal interfaces.

Later in 2015, Singh et al. [10] used aluminum powder of approximately 45 µm particle size in interfacing layer of aluminum substrates. Dense and identical joint was achieved through metallurgical bonding with specimens attributed to melting of powder particles.

Nickel based EWAC-1002 ET powder with average particle size of 50 µm was used as interface layer between 1018 MS specimens by Dwivedi et al. [12]. Within the stated range of process parameters proper fusion between Nickel based powder and base metal was achieved. Presence of Fe₃C, FeNi, and Cr₂₃C₆ phases were confirmed through XRD analysis.

Gupta et al. [6] used various interfacing powders during experiments viz. cast iron, nickel sulphate, nickel carbonate, and zinc sulphate to obtain MS-SS joints. However, poor coupling of interface powder with base materials was a prime concern in all such joints. But EWAC-1002 ET with particle size of 40 µm was coupled well with base material to form good welded joint.

Srinath et al. [14] used Nickel based powder as filler material to join dissimilar metals (MS and SS-316) with particles size of 40 µm. The dielectric properties of sandwich layer significantly manipulated after formation of various carbides, oxides and intermetallics during interaction of microwaves with metallic powder. Thus coupling of microwaves in sandwich layer enhanced, which further resulted in localized melting and good joint formation.

SS-316 in powder form with particle size of 50 µm as interfacing material was used by Bansal et al. [15] to join MS and SS-316. Chromium has strong affinity to react with carbon at high temperature to form chromium carbide as confirmed through XRD analysis. Formation of intermetallics like NiFe₂O₄ credited to atmospheric heating condition during processing.

Bansal et al. [17] used an interlayer of SS-316 of approximate particle size of 50 µm in between the specimens of SS-316. Microwave processed joints showed better properties when the filler material used for joining is of same composition as that of parent material to be joined.

With average particle size of 30 µm, Inconel 718 in powder form was used as filler material in joining process of Inconel 718 and SS-316 L using EM energy by Bansal et al. [19]. Presence of chromium (Cr) and aluminium (Al) in Inconel-718 was responsible for formation of oxide layer on faying surface of it. The flux UV 420 TT (composition: SiO₂+TiO₂ (15 wt %), CaO+MgO (35 wt %), Al₂O₃+ MnO (21 wt %), CaF₂ (25 wt %)) was used to dissolve the oxide layer which further helps in wetting faying surfaces of candidate material.

Bansal et al. [22] used Inconel 718 in powder form with particle size of 30 µm as interfacing powder to join Inconel 718. During processing of metallic material, powder layer of interfacing material acts as a concentrated source of heat energy which facilitates the joining process of specimens.

EWAC Nickel based powder was used by Bagha et al. [24] while developing SS304-SS304 joints. Performance of these joints was compared with the 99.9% pure Nickel powder based joints. EWAC powder based joints showed higher weldability in comparison with pure Nickel powder based joints. Surface finish of joints obtained using EWAC powder was higher and bead size was negligible in comparison with pure Nickel based joints.

2.4 Experimental Set-up Based Developments:

Most of the work related to microwave joining has been performed using 900 W, 2.45 GHz domestic microwave applicator. However, some researchers have also used industrial microwave oven with different power levels. Experimental setups of MHH can be broadly classified into two categories viz., refractory brick based set-up and insulation box based set-up.

In refractory brick (insulation, alumina brick) based set-up, a slot is provided on top face of a refractory brick as drawn in Fig. 1. Specimens are placed inside this slot along with the interface material in between the specimens. Joint region is then covered by a graphite sheet. Metallic specimens reflect microwave radiations at room temperature. Therefore, to prevent direct contact of microwaves with metal, an additional insulation brick/element is also used to cover the specimens to be joined from above. Susceptor material such as charcoal powder is kept above the graphite sheet. Graphite sheet helps in avoiding mixing of susceptor material and interface material. It can also sustain high temperature of the burning lava of susceptor material during joining process. Another graphite sheet, if desired, can also be placed on bottom face of the joint zone in order to separate it from lower refractory brick. This whole setup is then placed into cavity of the microwave applicator. Placement of whole setup plays significant role in interaction with microwaves.

Insulation box based set-up require the use of a box made-up of low dielectric loss [19] material due to which microwaves can easily pass through the box without any interruption. Moreover, the box also acts as a thermal insulator and hence prevents the heat loss to surrounding. Specimens to be joined are generally placed in butt configuration and interfacing gap is filled with slurry of interfacing powder and epoxy resin. This assembly is then placed on graphite plate and further put inside the insulation box. Graphite plate is used instead of the small sized graphite sheet used in brick based set-up. Graphite plate acts as a separator between specimens and insulation box. It can also withstand high heat generated during the joining process. Finally, insulation box is kept inside the microwave oven and joining process is started [19].

In 1995, Siores and Rego [8] developed the experimental set-up for microwave joining of metals, ceramics and plastics. The magnetron with power of 2 kW was used to create arcing which was responsible for localized melting of thin steel specimens. For optimization of joining process the primary concern was focusing of microwave radiation at required location. In their prototype development they focused on microwave guide design and peripheral facilities. Attention was paid to design details that ensured minimum leakage of EM waves.

In 2010, Srinath et al. [18] discussed the experimental setup used for joining of austenitic stainless steel. After preparing specimens, they placed it on insulating material on turn table of domestic microwave applicator. To prevent the direct coupling of microwaves and parent metal, masking material was used by them. Charcoal powder was placed on the entire masking material and also on interfacing zone. Later in 2011, they modified setup with addition of solid graphite layer used to separate the interfacing zone from suscepting material.

A fixture was used by Bansal et al. [17] and whole arrangement was placed in hot zone of it to obtained joining of stainless steel. Material used for fixture was transparent material to microwaves and act as a thermal insulator. Alumina plate instead of graphite plate was used as a separator because it has high thermal as well as chemical stability and high melting point.

Gupta et al. [16] used a slot type experimental setup. In which they made a slot in refractory brick to place a specimens with interfacing material between them. Susceptor material was placed on the joint zone only. Rest of the specimen was covered with masking material.

Bagha et al. [25] modified the experimental set-up used by Gupta et al. [6]. They proposed the use of a vertical cavity type feeder for selective heating of target materials. Weldability was increased by using vertical type feeder mechanism in processing of metals. This set-up also helped in reducing process time due to selective and quick heating of target materials.

3. Research gaps and future directions:

Processing of metals in microwave oven using EM energy is a challenging task. Many potential problems are associated with microwave joining of metallic materials:

1. Theoretical modeling of microwave joining process requires sufficient inputs such as development of rational as well as empirical relations for calculating the heat flow rate into and out of the target materials, susceptor and specimens.

2. Software based simulation of microwave joining process requires more attention for accurately predicting the joining process parameters such as heat generation rate, heat flow rate, time required for joining etc.

3. Effect of using nano-powders as interface materials is not discussed earlier in literature.

4. More work is required in the area of joining large size specimens so as to make this process commercially viable for industrial applications.

5. Only a limited number of materials have been explored for microwave joining. Success of this process for joining many other materials is underway.

6. Mostly rectangular and circular cross-sections have been investigated for microwave joining. Other cross-sections can also be explored and compared for their effectiveness in this process.

7. Pre-heating helps in this process. But the amount of pre-heating required is not yet standardized.

8. Refractory bricks and insulation boxes used during this process work good for only 2-3 cycles and have to be thrown away after their deterioration due to repeated use. Better materials for bricks and boxes need to be investigated which should have long lifetime.

9. Standardization of the process is still not done by any regulating authority, which is a prime requirement for its industrial use.

4. CONCLUSION:

In this paper review of a number of research developments in microwave joining of metallic materials is presented. Developments related to size and shape of specimens have been investigated which shows that geometry of specimen plays an important role in the joining process. Different types of susceptor materials can be used for localized heating which initiates the joining process. Interfacing material of same composition as that of parent metal shows enhanced properties of microwave processed joints. Review of various experimental setups shows that vertical cavity type feeder results in quick selective heating of target materials. Further a number of inferences have been drawn upon that are useful in guiding possible future course of actions in microwave joining of metals.

5. REFERENCES:

1. Pathania A. Gupta D. A Review: Microwave energy for materials processing. International Journal of Scientific Research and Development 2014; 2 (9): 572–578.

2. Gupta M. Eugene W. W. L. Microwaves and Metals. Singapore: John Wiley and Sons (Asia) Pte Ltd. 2007.

3. Singh S. Gupta D. Jain V. Sharma A. K. Microwave processing of materials and applications in manufacturing industries : A Review. Materials and Manufacturing Processes 2015; 30: 1–29.

4. Mishra R. R. Sharma A. K. A review of research trends in microwave processing of metal-based materials and opportunities in microwave metal casting. Critical Review in Solid State and Material Science 2016; 41 (3): 217–255.

5. Sharma A. K. Srinath M. S. Kumar, P. Microwave joining of metallic materials 2009, application 1994/ Del/ 2009.

6. Gupta P. Kumar S. Kumar A. Study of joint formed by tungsten carbide bearing alloy through microwave welding. Materials and Manufacturing Processes 2013; 28 (5): 601–604.

7. Clark D. E. Suttan W. H. Microwave processing of materials. Annual Review of Material Science 1996; 26: 299–331.

8. Siores E. Do Rego D. Microwave applications in materials joining. Journal of Materials Processing Technology 1995; 48 (1–4): 619–625.

9. Srinath M. S. Sharma A. K. Kumar P. A new approach to joining of bulk copper using microwave energy. Materials and Design 2011; 32 (5): 2685–2694.

10. Singh S. Suri N. M. Belokar R. M. Characterization of joint developed by fusion of aluminum metal powder through microwave hybrid heating. Materials Today: Proceedings 2015; 2 (4–5): 1340–1346.

11. Bansal A. Sharma A. K. Kumar P. Das S. Joining of mild steel plates using microwave energy. Advanced Materials Research 2012; 585: 465–469.

12. Dwivedi S. P. Sharma S. Effect of process parameters on tensile strength of 1018 mild steel joints fabricated by microwave welding. Metallography, Microstructure and Analysis 2014; 3 (1): 58–69.

13. Bansal A. Sharma A. K. Das S. Metallurgical and mechanical characterization of mild steel-mild steel joint formed by microwave hybrid heating process. Sadhana - Academy Proceedings in Engineering Science 2013; 38 (4): 679–686.

14. Srinath M. S. Sharma A. K. Kumar P. Investigation on microstructural and mechanical properties of microwave processed dissimilar joints. Journal of Manufacturing Processes, 2011; 13 (2): 141–146.

15. Bansal A. Sharma A. K. Kumar P. Das, S. Investigation on microstructure and mechanical properties of the dissimilar weld between mild steel and stainless steel-316 formed using microwave energy. Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture 2014; 230 (3): 439–448.

16. Gupta P. Kumar S. Investigation of stainless steel joint fabricated through microwave energy. Materials and Manufacturing Processes 2014; 29 (8): 910–915.

17. Bansal A. Sharma A. K. Kumar P. Das S. Characterization of bulk stainless steel joints developed through microwave hybrid heating. Materials Characterization 2014; 91: 34–41.

18. Srinath M. S. Sharma A. K. Kumar P. A novel route for joining of austenitic stainless steel (SS-316) using microwave energy. Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture 2011; 225 (7): 1083–1091.

19. Bansal A. Sharma A. K. Das S. Kumar P. On microstructure and strength properties of microwave welded Inconel 718/stainless steel (SS-316L). Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications 2015; 230 (5): 939–948.

20. Bansal A. Sharma A. K. Kumar P. Das, S. Application of electromagnetic energy for joining inconel 718 plates. Journal on Mechanical Engineering 2012; 2 (4): 18–24.

21. Badiger R. I. Narendranath S. Srinath M. S. Joining of inconel-625 alloy through microwave hybrid heating and its characterization. Journal of Manufacturing Processes 2015; 18: 117–123.

22. Bansal A. Sharma A. K. Kumar P. Das S. Structure–property correlations in microwave joining of inconel 718. Journal of Minerals, Metals and Materials Society 2015; 67 (9): 2087–2098.

23. Rana V. Sandhu C. S. Investigation on microstructural and micro hardness of microwave welded joint of EN-31. International Journal of Latest Trends in Engineering and Technology 2015; 5 (1): 112–117.

24. Bagha L. Sehgal S. Thakur A. Comparative analysis of microwave based joining/welding of SS304-SS304 using different interfacing materials. MATEC Web Conference 2016; 57 (3001): 1–4.

25. Bagha L. Sehgal S. Thakur A. Kumar H. Effects of powder size of interface material on selective hybrid carbon microwave joining of SS304–SS304. Journal of Manufacturing Processes 2017; 25: 290–295.

26. Saxena S. Bansal S. Deo R. Khan S. Joining of bulk metallic pipes by microwave hybrid heating process under parametrical regulations. International Organization of Scintific Research-Journal of Mechanical and Civil Engineering 2014; 11 (6): 62–69.

Received on 09.08.2017 Accepted on 29.09.2017

Research J. Engineering and Tech. 2017; 8(3): 282-290.

DOI: 10.5958/2321-581X.2017.00048.4