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Author: search.filters.author.Mishra, Radha RamanSubject: search.filters.subject.Microwave energy

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    Unraveling atomistic heating behavior of vacancy induced 3C-SiC during microwave exposure
    (Elsevier, 2025-01) Mishra, Radha Raman; Roy, Tribeni
    This study explores the impact of pre-existing silicon and carbon vacancies on the microwave heating of 3C-SiC at an atomistic level using molecular dynamics simulations. Microwaves were introduced at different electric field strengths (0.1 and 0.5 V/Å) and different frequencies (100, 150, 200, 250 and 300 GHz) to the vacancy-induced 3C-SiC crystal to understand its heating characteristics. During microwave exposure, the temperature of the 3C-SiC crystal increased rapidly with increasing Si vacancies, electric field strength, and frequency. The results revealed that 3C-SiC crystals having 1.5 % and 2.0 % Si vacancies undergo 40–50 % physical and structural change with the application of microwave for 4.985 ns and 4.49 ns, respectively, at 0.5 V/Å and 300 GHz. Additionally, a comparative analysis was performed to study the microwave heating rate of 3C-SiC with Si and C vacancies (1.5 and 2.0 %). C vacancies at 1.5 % and 2.0 % showed 95.5 % and 142.2 % higher heating rates, respectively, than Si vacancies. Additionally, beyond 1000 K, microwave heating is driven by structural changes induced by vacancies as compared to the thermal conductivity of the 3C-SiC crystal.
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    Microwave Processing of Materials Fundamentals and Applications
    (Taylor & Francis, 2022) Mishra, Radha Raman
    The use of microwave energy in material processing is increasing gradually due to numerous benefits over conventional energy sources. Volumetric heating characteristic of microwave energy while processing engineering materials has been explored in various manufacturing processes such as sintering, casting, joining, drilling and cladding. However, the fundamentals associated with microwave heating of materials are less explored. The present chapter summarizes most of the significant fundamentals of microwave-material interaction and heating phenomena that occur during microwave energy absorption in materials. Various microwave energy-based applications are discussed.
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    Processing of Composite Materials Using Microwave Energy
    (CRC Press, 2022) Mishra, Radha Raman
    Composite materials are being popularly used in the fabrication of various industrial components. Most of the manufacturing techniques used for developing parts involve the interaction of heat with the constituent materials through heat transfer. Such processing methods result in non-uniform heating of materials; subsequently, various defects are incurred in the developed products. The use of microwave energy while developing composite materials may overcome these challenges as it offers volumetric and rapid heating and significant saving of time and energy. The present chapter summarizes various fundamentals of microwave-material interaction and heating of different composite materials during microwave processing. Heating mechanisms involved in processing composites such as metal matrix composites, ceramic matrix composites, and polymer matrix composites have been discussed. Challenges in the processing of composite materials have been highlighted, and further research directions have been outlined.
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    Thermal analysis of in-situ microwave casting for efficient processing
    (Elsevier, 2018) Mishra, Radha Raman
    In the present work, in-situ microwave casting was analyzed for higher efficiency while aluminum casting at 2.45 GHz and 1400 W. Models of setup with different insulation arrangements were generated using a software tool. Simulation was carried out to find the optimum casting conditions. Results revealed that complete insulation of mold assembly enhances energy saving and reduces melting time; however, higher mold preheating results in longer solidification time and coarse grains in the cast. Mold assembly without insulation showed poor efficiency. Optimum results were obtained in a mold assembly consisting insulated pouring basin and charge with bare mold and sprue
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    Characterization of SiC-Reinforced AZ91 Magnesium Alloy Composites Produced Using In situ Microwave Casting
    (Springer, 2021-02) Mishra, Radha Raman
    Magnesium-alloys-based metal matrix composites (MMCs) are one of the most researched materials for producing industrial components due to their high specific strength. In recent years, microwave energy has been used for processing of various materials including polymers, ceramics, metals, and composites owing to significant saving of energy and time as compared to the conventional processes. In the present work, microwave energy at 2.45 GHz was used to fabricate AZ91 magnesium-alloy-based MMCs. The AZ91 magnesium alloy (bulk) pieces were hybrid heated inside a microwave applicator at 1400 W. The melt was processed with silicon carbide (SiC) and allowed to pour into a graphite mold. The produced composites were characterized to study their microstructural properties. The microstructural characterization of the composites revealed that distribution of SiC particles is uniform. Finer grains were achieved in the composite as compared to as-received alloy. The presence of SiC, Mg2Si, Mg2C, Mg2C3, Mg17(Al, Zn)12, and α-Mg phases was confirmed in the composite through energy-dispersive X-ray spectroscopy analysis. The micro-indentation hardness of the composite was found as 206 ± 28 HV which is higher than as received alloy.
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    On microstructural and mechanical properties of 21-4-N nitronic steel joint developed using microwave energy
    (Sage, 2021-07) Mishra, Radha Raman
    In the current experimental work, an effort has been made to explore the feasibility of fusion joints of 21-4-N nitronic steel employing microwave heating. These fusion joints were developed inside a domestic microwave applicator operating at 900 W. Microwave energy was used to fabricate the joints in hybrid heating mode by converting electromagnetic energy into heat at 2.45 GHz. Charcoal and SiC plates were used as susceptor and separator, respectively, and nickel powder was used as the interface material. The developed joints were characterized for their microstructural and mechanical properties. The microstructures indicate a complete fusion of nickel interfacing powder with the faying surfaces. XRD results show the formation of metallic nitrides and carbide phases (Cr2N, Fe3N, and Fe2C) and the FeNi phase at the weld zone. Furthermore, the observed average tensile strength of the fusion joints was approximately 61% of base metal. The reduction in the stress and elongation compared to the base metal were 38.67% and 12.68%, respectively. The average microhardness of the microwave joints was monitored as 407 ± 69.27 HV. The results indicate the feasibility of fusion joints of nitronic steel using microwave energy.
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    Effect of input microwave power and insulation on microstructure and tensile properties of cast Al 7039 alloy produced at 2.45 GHz
    (Taylor & Francis, 2020-10) Mishra, Radha Raman
    In the present work, microwave energy was used for casting Al 7039 alloy at 2.45 GHz in the ambient cavity environment. Effects of input power and insulation of the mould assembly during irradiation on charge melting and mould preheating were studied. Five different casts were produced at 1000 W, 1200 W, 1400 W, 1400 W with an insulated pouring basin and 1400 W with insulated mould assembly. Melting time of the charge was the least while using 1400 W with insulated mould assembly, whereas preheating of the mould was observed minimum during casting at 1400 W inside an insulated pouring basin. Cast microstructures revealed that less preheating of the mould resulted in finer grains and intermetallics, which improve tensile properties of the cast. Fractographic analyses showed the presence of coarse intermetallics in the casts produced with insulated mould assembly, which resulted in significant reduction of tensile properties.
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    Effect of susceptor and mold material on microstructure of in-situ microwave casts of Al-Zn-Mg alloy
    (Elsevier, 2017-10) Mishra, Radha Raman
    In-situ microwave casting is a novel technique; it is based on the principles of microwave hybrid heating. The dynamics of the process and the cast quality are significantly influenced by the materials used in the microwave irradiation. In the present work, role of susceptor and mold on exposure time, melting time, mold preheating and cast properties is studied. Physics of the process in the context of exposure time and mold materials is discussed. The aluminum alloy 7039 casts were developed in ambient atmosphere inside an applicator using microwaves at 2.45 GHz and 1400 W. Charge was hybrid heated using susceptors – SiC and ceramic crucible to melt and cast in-situ in the preplaced alumina and graphite molds. Characterization reveals that grain structures of the casts were influenced by mold preheating and mold material. Finer grains with higher micro-pores were observed in the casts developed in alumina mold with SiC susceptor. The casts contain MgZn2, Mg2Si, Al3Fe and Al8Fe2Si as intermetallics; however, their distribution and size depend upon the cooling pattern of the melt. Microindentation hardness of the casts developed in alumina mold with SiC susceptor was observed to be the highest (146 ± 10 HV) among the developed casts.