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Title: Development and Characterization of Microwave Processed Cavitation Erosion Resistant Cladding
Authors: Bansal, Sandeep
Supervisor: Gupta, Dheeraj
Jain, Vivek
Keywords: Microwave Cladding;Composite Clads;Fractographic Analysis;Characterization;Taguchi L9 orthogonal array
Issue Date: 9-Sep-2022
Abstract: Hydroelectric power plants are experiencing huge revenue losses due to the failure of various components caused by cavitation erosion wear. The turbine is the primary components of any hydroelectric power plant and it fails catastrophically due to severe damage caused by cavitation erosion wear. The some of the well-established/ ongoing developments in the advanced surface engineering techniques have provided an effective solution to enhance the cavitation erosion resistance for the cavitation prone components. However, the improvement in wear resistance of the functional surfaces through coating/cladding with suitable overlaying material would be one of the most straightforward and economical solution. The conventional coating/cladding processes have many drawbacks such as excessive substrate deformation, high porosity, lower deposition efficiency, weak adhesion strength, poor fracture toughness, higher costs, and production of toxic gasses. Therefore, the coating/cladding by a novel method, that can overcome the drawbacks of existing methods, is needed. Microwave cladding process has the potential to overcome the maximum limitations of the conventional surface processing techniques. Hence, in the present study, the microwave processed composite clads of Ni-based (EWAC) as matrix material with variable weight percentage of reinforcements such as Cr3C2, WC10Co2Ni and Al2O3 on SS-316 substrate were developed. For this purpose, a domestic microwave oven with 2.45 GHz frequency and variable power from 180 W to 900 W was used. The charcoal powder was used as susceptor material. The percentage of reinforcements were varied from 0-30% (by wt%) for Cr3C2 and WC10Co2Ni with an increase of 10% step; and 0- 15% (by wt%) for Al2O3with an increase of 5% step. The cladding process parameters such as microwave power and exposure time influences the quality of clads. Therefore, prior to the development of the clads the parameters for defect free and good metallurgical bonded clads were optimized. iv The prepared clads were examined for microstructure, phase quality and quantity, porosity, microhardness, flexural strength (bonding strength) and cavitation erosion resistance at different parametric conditions. The probe sonicator-vibratory ultrasonic apparatus was used for indirect acoustic cavitation erosion testing. The optimization of process parameters revealed that an increase in power level significantly decreases the required processing time. The minimum exposure microwave power 900 W is required to melt the powder material system and partial amount of substrate material to cause the dilution for development of metallurgical bonded clads. The processing time required for the metallurgical bonded clads varies from 390 s to 590 s, for metallurgical characterization specimens, for different ceramic/cermets based composites. The least processing time of 390 s for Ni based-30Cr3C2 and highest processing time of 590 s for Ni based-15Al2O3 were required. Similarly, for the same compositions, the processing time required for tribological characterization specimens was 700 s and 790 s; and for flexural studies specimens was varied from 1200 s and 1445 s. The microstructure analysis reveals that all the developed composite clads are almost free from all types of cracks (interfacial and solidification cracks) and the potential of the process for clads thickness varies from 520 µm to 1090 µm. The highest and least thickness was achieved for Ni based-15Al2O3 and Ni based 10 WC10Co2Ni clads, respectively. The results of porosity analysis show that the developed composite clads possess significantly less porosity as compared to conventionally used cladding/coatings processes. The XRD analysis confirms the presence of Cr2Ni3, Cr23C6, Cr7C3, CrSi, CrSi2, SiO2, NiC, SiC, Cr3Ni2SiC phases in the Ni-based and Cr3C2 reinforced composite clads; and phases NiCo2O4, Ni2W4C, Ni2Si, NiAl2O4, W2C, Ni3Si, Cr3C2, and FeNi in Ni-based and WC10Co2Ni reinforced composite clads; and phases: Intermetallics (Ni3Si, FeNi3, and Fe7Ni3), Carbides (Fe5C2) and Oxides (Al2O3 and SiO2) in Ni-based and Al2O3 reinforced composite clads are developed. The formation of various carbides, silicides and v intermetallics during microwave hybrid heating led to higher average microhardness of the developed composite clads. The average microhardness of the developed Ni-based/30 WC10Co2Ni composite clad comes out to be highest (925±57 HV) among all the developed clads, which is almost 4.91 times higher than that of the substrate (SS-316). The presence of high strength carbides and intermetallics in the composite clads also resulted in the higher flexural strength of these clads. The value of flexural strength in case of Ni-based-15 Al2O3 composite clad was highest and it is of 854±16 MPa. The functional characterization results, in terms of vibratory cavitation erosion testing at varying test parameters (stand-off distance, vibration amplitude and horn immersion depth) revealed that cavitation erosion resistance (CER) of all selected composition developed composite clads is higher than the SS-316 substrate. The Ni-based-30 WC10Co2Ni composite clad shows highest CER among all the developed clads, which is almost 12.78 times higher than the substrate. The ANNOVA results revealed that all the three test parameters were significant for cavitation erosion wear. The stand-off distance (SOD) comes out to be the most influential test parameter followed by vibration amplitude (AMP) and horn immersion depth (IMD). The maximum cavitation erosion wear occurs at 0.5 mm SOD, 60 AMP and 80 mm IMD. The overall results led to the conclusions that the microwave energy proved its successful utilization to develop clads of various materials that can resist the cavitation erosion wear successfully. Hence, the microwave processed composite clads can be successfully used in hydroelectric power plant applications.
Appears in Collections:Doctoral Theses@MED

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