1. Ph.D Theses
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Item Studies on Corrosion, Mechanical and Wetting Properties of the Thermal Sprayed Coatings on Low Carbon Steel(National Institute of Technology Karnataka, Surathkal, 2021) A, Amudha.; Shashikala, H D.; Nagaraja, H S.Low-carbon or mild carbon steels are very attractive materials throughout the industrialized world in diverse applications but are susceptible to corrosion. This problem can be mitigated and the service lifetime of the low carbon steel can be increased by the application of protective coatings with good mechanical properties while reducing maintenance costs. In the present work, different corrosion-resistant materials like metal alloy (Inconel-625), ceramic-metal composite 25(NiCr)-75Cr3C2 and ceramic-graphene oxide nanoplatelets(GNP) composite (Al2O3-GNP and ZrO2-GNP) were coated using thermal spray techniques like weld overlay, High-Velocity Oxyfuel (HVOF), and Atmospheric Plasma Spray (APS) techniques respectively. The structural, morphological and compositional studies were carried out by XRD, FTIR, Raman Spectroscopy, XPS, FESEM-EDAX, TEM, and BET characterization techniques. The corrosion studies were conducted using the three-electrode electrochemical system. The stability of the coatings was studied using immersion tests upto 14 days. The mechanical and wetting properties of samples were studied using Vicker’s microhardness tester and contact angle measurements respectively. ANSYS FEA simulation showed that alternate skip weld overlay of SS-309Mo as the buffer layer by GTAW and Inconel-625 as final layer by SMAW process for the 6 mm thick low carbon steel substrate preheated to 100°C, to be the best model with 18 MPa surface residual stress among twelve combinations. Using the conditions of the best model, SS-309Mo and Inconel-625 have been coated on low carbon steel. The weld overlay coated Inconel-625 had nearly the same corrosion resistance as that of bulk Inconel-625 with increased microhardness. 25(NiCr)-75Cr3C2 cermet coating on low carbon steel using HVOF process showed hydrophobic behaviour with improved microhardness and corrosion resistance. The α-Al2O3- (X wt. %GNP) and ZrO2-(X wt. %GNP) (where X= 0, 0.5, 1.0, 1.5 and 2) composite coatings by APS process were successful in the retention of GNPs in the composite. The surface corrosion resistance increased by six orders of magnitude when coated with 2.0 wt.% GNP reinforced α-Al2O3 nanocomposite, in comparison with bare Al2O3 coating. The increase in corrosion resistance is due to the hydrophobic nature of in-situ reduced GNP. In addition, the mechanical properties have improved with the addition of GNP. The corrosion rate of ZrO2-2 wt. % GNP coating is 130 times lesser than that of ZrO2. Further, the mechanical and wetting properties of the coatings showed a similar trend as that of corrosion behaviour.Item Effect of Reinforcement Corrosion on the Bond Strength of RC Members(National Institute of Technology Karnataka, Surathkal, 2014) Shetty, Akshatha; Venkataramana, Katta; Narayan, K. S. BabuCorrosion of reinforcing steel is the most detrimental effect endangering the structural performance. Present investigation has been taken up to study the detrimental effect of corrosion on bond behaviour. Anchorage bond strength and Flexural bond strength characteristics are studied in this research. Two types of cements namely Ordinary Portland Cement (OPC) and Portland Pozzolona Cement (PPC) have been used. Bond strength study has been carried out for controlled beam specimen and for specimens subjected to different levels of corrosion. Loss in mass of reinforcement bar has been taken as the basis to fix corrosion levels. Accelerated corrosion technique has been adopted to control corrosion rate by regulating current over predetermined durations. For the study of anchorage bond strength, cylindrical specimens have been adopted. Concrete grade of M20 and Fe-415 grade of 16mm diameter bar have been used. From the study it has been observed that for corrosion levels upto 2.5%, bond strength is unaffected. But for corrosion levels beyond 2.5%, there is considerable decrease in bond strength. For understanding the performance of flexural bond strength, National Bureau of Standard (NBS) beams have been investigated. Concrete grade M30 and steel Fe-415 have been used. From the experimental investigation it has been observed that load carrying capacity drops by about 1.6%, for every percentage increase in corrosion level. Bond strength degradation of 2.6% at slip initiation and 2.1% at end of slip have been observed for every percentage increase in corrosion level for OPC concrete beam specimens. For PPC concrete, bond strength degradation of 2% at slip initiation and 2.1% at end of slip have been observed. In numerical study, finite element method was used. ANSYS commercial software is used for the study. From the numerical modelling it has been observed that load carrying capacity drops by about 1.8%, for every percentage increase in corrosionlevel. The bond strength degradation values are 3% and 2.4% at initiation of slip and end of slip respectively per percentage increase in corrosion level. Lastly, an attempt has been made to apply the proposed prediction equations to estimate corrosion in real life structures.