2. Thesis and Dissertations
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Item Effect of T6 Heat Treatment on Corrosion of Al-SiC p Composite & Inhibition Evaluation of Benzimidazole & Its Derivatives(National Institute of Technology Karnataka, Surathkal, 2017) Chacko, Melby; Nayak, JagannathaAluminium alloys, particularly 6061, reinforced with SiC have been the focus of the attention because of their application potential in an extensive range of demanding applications, such as automobiles, aerospace, and defense. There are many other applications which involve exposure of the composites to the potential corrosive environment. Because of the duplex nature of the composites, they are prone to accelerated corrosion compared to their monolithic counterpart. Corrosion of these composites not only limit their service life but also lead to deterioration of their unique mechanical properties for which they are designed. Studies reveal the role of micro structural changes and processing routes on the corrosion behaviour. Also, aging treatment was found to have an influence on the corrosion rate as the heat treated samples showed higher corrosion rates as compared to the non-treated samples. Corrosion studies in organic acid solutions are rare in comparison with similar studies in mineral acids. Acetic acid is a frequently used organic acid in many industrial processes. At high temperatures, these acids dissociate, generating new aggressive ions which cause faster corrosion and they can provide sufficient protons to act as true acids. Adding inhibitors to the corrosion medium is a general practice for the corrosion protection. Heterocyclic organic compounds which contain oxygen, sulphur, phosphorous, nitrogen and aromatic rings are considered to be the most active and resourceful inhibitors in the acidic corrosive medium for the metals, alloys, and composites. Latterly, benzimidazole and its derivatives have established a considerable reputation on their corrosion inhibition properties for metals and alloys, owing to the existence of aromatic rings and nitrogen atom. In the present study benzimidazole (BI), 2-methylbenzimidazole (2-CH3-BI), and 2- mercaptobenzimidazole (2-SH-BI) are used as inhibitors. Aging profile of T4 and T6 treated Al-SiCp was obtained using Rockwell B hardness. Under-aging, peak-aging, and over-aging temperatures and time were found out. Samples were corrosion tested and found to be susceptible to corrosion in acetic acid where peak-aged samples exhibited higher corrosion and over-aged samples8 showed minimum corrosion. Three inhibitors were tested for their efficiency. Results proved that they are excellent inhibitors. The maximum inhibition efficiency obtained using BI was 66%, 69% offered by 2-CH3-BI and 75% was achieved in the presence of 2-SH-BI. Inhibition efficiency of inhibitors followed the order of 2-SH-BI > 2- CH3-BI > BI. Activation energy, enthalpy, entropy, and free energy of adsorption were calculated for all experimental conditions. Results suggest that inhibitors get adsorbed on the composite surface by mixed adsorption, where chemisorption is predominant.Item Growth and characterization of DC magnetron sputtered Ni-Ti intermetallic and near equiatomic thin films(National Institute of Technology Karnataka, Surathkal, 2018) Reddy, B. Naveen Kumar; Udayashankar, N. K.In recent years NiTi thin films have attracted much attention as intelligent and functional materials because of their unique properties such as shape memory effect. Shape memory alloy thin films possess several desirable properties such as high power to weight (or force to volume) ratio, and ability to recover large transformation stress and strain upon heating and cooling, pseudoelasticity (or superelasticity), high damping capacity, good chemical resistance and biocompatibility, etc. In spite of the development of advanced deposition techniques for NiTi thin films, some unresolved issues still remain, which limit precise control of composition during the deposition. In order to standardize these deposition techniques, an advanced understanding of the underlying process-property relationships are essential. This thesis mainly describes the growth and characterization of DC magnetron sputtered intermetallic, and near equiatomic NiTi alloy thin films. The correlation between deposition parameters and material properties has been established. In this thesis work, we have mainly investigated the influence of post-deposition conditions (annealing temperature and/or aging time) on NiTi thin film micro-structure, surface morphology, mechanical and surface properties. Based on XRD, it was concluded that annealed and aged intermetallic and near equiatomic NiTi thin films were crystallized, resulting in the form of various dominant phases along with intermetallic precipitates. The surface morphology of the investigated intermetallic and near equiatomic NiTi thin films from FESEM characterization was found to vary significantly with respect to annealing temperature and/or aging time. Topographical structures can be altered by varying the annealing temperature and/or aging time. The surface mean height (Ra), root mean square (RMS) and maximum peak to valley height (P-V) values have been obtained by AFM characterization. Nanoindentation tests on annealed and aged intermetallic and near equiatomic NiTi thin films were performed at room temperature. The hardness and elastic modulus values of deposited films increase probably due to formation of the intermediate metastable states by the incomplete alloying process. X-ray photo electron spectroscopy (XPS) was used to study the composition and surface chemistry of the annealed films. From HR-XPS investigations, it was observed that annealed and/or aged intermetallic and near equiatomic NiTi thin films had higher affinity to form Titanium dioxide (TiO2) layer on the film surface leaving a Nickel enriched matrix immediately behind the metal oxide layer along with carbide precipitates.