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Title: Development and Characterization of Functionally Graded Materials by Microwave Heating
Authors: Kaushal, Sarbjeet
Supervisor: Gupta, Dheeraj
Bhowmick, Hiralal
Keywords: Microwave Cladding;Functionally Gradient;Composite;Tribology
Issue Date: 2-Sep-2019
Abstract: Stainless steel plays a vital role in almost every manufacturing industry worldwide. Austenitic stainless steel represents more than 2/3rd of the total stainless steel world production. Austenitic stainless steels are widely used in many applications due to their excellent corrosion and oxidation resistance. However, this grade of steels has poor wear resistance properties under severe wear working environment and hence causes huge economical loss to the developing countries. The functional properties of these steels can be improved by overlaying the coatings/claddings of wear resistant materials. However, these claddings/coatings generally fail due to the existence of sharp interface. The functionally graded material (FGM) claddings eliminate this problem by replacing the sharp interface with the transition interface. The FGM claddings can be processed through various techniques like powder metallurgy, vapor deposition, centrifugal method, laser cladding etc. However, these techniques are associated with some limitations such as lower deposition efficiency, higher cost (in case of laser cladding), production of toxic gases, higher processing time (in case of vapor deposition technique). The development of alternating material processing technique with lower manufacturing cost, lower processing time and environmental friendliness is the need of the hour. Microwave processing of materials has emerged as a noble processing technique in the past few years. The heating effects of microwave energy were discovered in the mid of year 90’s and with the discovery of microwave oven, the microwaves were successfully utilized in the cooking of food. Due to lower processing time and better efficiency, the utilization of domestic microwave oven spread throughout the world during 1980-1990. At the same time, the commercial applications were discovered such as vulcanization of rubber, wood drying, chemical processing, etc. With the continuous efforts of researchers, the microwave applications were used in the field of sintering of ceramics and ceramic based materials. However, the microwave sintering was only confined to the ceramic-based materials, while the processing of metallic materials through microwave heating was unsuccessful due to their lower skin depths. However, researchers developed a microwave hybrid heating technique to process the metallic materials. But still, microwave processing of metallic materials is challenging task at a lower frequency and lower power. A lot of work has been reported in the field of microwave joining and cladding of metallic-based powders. The microwave cladding was also carried out to produce the composite claddings on the metallic based substrate. The microwave cladding further motivated the researchers to further explore the potential of microwave heating in the field of development of FGMs. In the present work, the microwave energy was utilized to develop the functionally graded clads (FGCs) of various metal ceramic-based materials. The multimode type domestic microwave oven with a frequency range of 2.45 GHz and variable power of 180-900 W was used as the microwave applicator. The Ni-based EWAC powder was selected as the matrix material and silicon carbide (SiC), tungsten carbide (WC8Co) and chromium carbide (Cr3C2) ceramics were used as reinforcement materials. The four-layered FGCs of Ni based/SiC, Ni based/WC8Co and Ni based/Cr3C2 composites with varying compositions of reinforcements from 0-30% (by wt%) in the step of 10% were developed. The matrix and reinforcements were premixed in a mechanical mixture to obtain the different layers such as Ni based-100%, Ni based + 10% SiC, Ni based + 20% SiC and Ni based + 30% SiC. The different functionally clad layers were developed step wise step using the microwave hybrid heating technique with charcoal as susceptor materials. The developed FGCs were characterized using various relevant techniques to study microstructural characterization (using scanning electron microscope equipped with EDS), X-ray diffraction pattern (phase analysis), functional characteristics (dry sliding wear behavior), and mechanical properties (micro-hardness and flexural strength). The XRD study revealed that the formation of various hard compounds such as carbides silicides during microwave hybrid heating. In case of Ni based/SiC FGC, the formation of the highest peak of Ni3Si2 phase was observed. While in case of Ni based/WC8Co FGC, the highest peak observed was Ni4W. Similarly, in case of Ni based/Cr3C2 FGC the formation of Ni3C and Ni3Cr2 was observed. The microstructure analysis of the microwave processed FGC revealed the gradient structure of various FGCs layers. The equiaxed grains were seen throughout the microstructure of the FGCs, this was due to the volumetric heating associated with microwave heating which restricted the transition of equiaxed structures to dendritic structures. The EDS analysis of FGCs revealed the presence of various carbides in the matrix region of the FGC layers. The results of EDS line mapping confirm the presence of a maximum amount of reinforcement in the top layer of FGC, while a higher amount of Ni metal is present in the bottom layer of FGC. The formation of various carbides and silicides during microwave hybrid heating led to higher micro-hardness of the FGCs. In case of Ni based/WC8Co, the micro-hardness profile revealed the maximum value (880 ± 30 HV) of micro-hardness in the top FGC layer. The Ni based/Cr3C2 FGC reveals the maximum micro-hardness of 576 ± 25 HV in the top clad layer. The Ni based/SiC FGC exhibited maximum micro-hardness (1020 ± 30 HV) in the top FGC layer. Presence of high strength carbides and intermetallics in the microwave processed FGCs resulted in the higher flexural strength of these FGCs. The average value of flexural strength in case of Ni based/WC8Co FGC was 764 ± 4 MPa with deformation index of 2.2× 10-4 mmN-1. On the other hand in case of Ni based/Cr3C2 FGC, the average flexural strength was 710.5 ± 10 MPa with deformation index of 2.1× 10-4 mmN-1. The average flexural strength of the Ni based/SiC FGC was 771.2 ± 5 MPa with deformation index of 2.7× 10-4 mmN-1. The functional characterization (in terms of dry sliding wear tests) results revealed lower wear rate in FGCs than single layer clads and the SS-304 substrate. The Ni based/SiC exhibited better wear resistance than all other FGCs. The overall results led to the conclusions that the microwave energy was successfully utilized to develop the FGCs of various materials. The developed FGCs can be used in many industrial applications where higher strength and wear resistance are required.
Description: Ph.D. Thesis
Appears in Collections:Doctoral Theses@MED

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