Faculty Publications
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Item Effect of aging and protective coating on the corrosion behavior of 6061 Al / SiCp composite in chloride solutions(Trans Tech Publications Ltd ttp@transtec.ch, 2011) Rajasekaran, S.; Udayashankar, N.K.; Nayak, J.Metal matrix composites considered especially for marine application are typically aluminum-based. Utilization of the composites in marine environments requires adequate corrosion resistance. In this work, the effect of aging and aluminum as resistive coating on the corrosion behavior of 6061 Al / SiC p composite in 1N and 3.5N NaCl solution in the temperature range of 30°C-50°C is studied by means of electrochemical techniques, scanning electron microscope (SEM) and weight loss measurements. Aging results in precipitation of intermetallics in the matrix, this in turn leads to galvanic and pitting corrosion. Pitting initiation and propagation as the main corrosion mechanism was driven by the aging kinetics which is ruled by the reduction in the retained vacancy concentration and at the same time by dislocation density due to the presence of SiCp. Sputtered aluminum coating on the composite effectively resists the pitting initiation and propagation and hence corrosion process. Also the intermetallic precipitates are unexposed to the Chloride solution by the presence of aluminum coating. Hence aluminum coating acts as corrosion resistive coating for the 6061 Al / SiCp aged composites. © (2011) Trans Tech Publications.Item Equal channel angular pressing of aluminum-alumina insitu metal matrix composite(Trans Tech Publications Ltd ttp@transtec.ch, 2012) Athreya, C.N.; Mahesh, V.P.; Brahmakumar, M.; Rajan, T.P.D.; Prabhu, K.N.; Pai, B.C.; Gupta, R.K.; Ramkumar, P.The present investigation is on synthesis of in situ Al-alumina composite and to evaluate the effect of equal channel angular pressing on the refinement of the grain structure and enhancement in the hardness and the strength. The billets pressed in as cast condition has shown cracks during first pass. The billets pressed immediately after solution treatment for one pass and followed by ageing treatment immediately after pressing exhibited very high hardness of 125BHN against 95 BHN to that of the T6 condition of 6061 aluminium alloy. The microstructural refinement from 35 μm to 11 μm is obtained in annealed and ECAP 2 pass condition. © (2012) Trans Tech Publications.Item Effect of plastic strain and processing routes on the hardness of as-cast aluminum(American Institute of Physics Inc. subs@aip.org, 2020) Valder, J.; Rijesh, R.; Kumar, P.; Saminathan, S.; Raju, K.; Surendranathan, A.O.In the present study, Equal Channel Angular Pressing (ECAP) of commercially pure aluminum (Al) in the cast form was carried out at room temperature for assessing its hardness by different routes and passes. The different routes employed in the present investigation are A, BA, BC and C. The Al specimens were pressed by a die of 150° channel angle without back pressure with Molybdenum disulfide (MoS2) as the lubricant. ECAP has significantly improved the hardness of Al in the subsequent passes. It has been observed that the hardness has been increased after first pass at room temperature from 47 VHN in the annealed condition to 54 VHN and after the second pass the hardness value has been increased to 56, 57, 62 and 56 VHN for routes A, BA, BC and C respectively. The increase in the hardness may be attributed to the severe fragmentation of microstructure of cast Al and the change in the orientation of the specimen from one pass to the next pass. After one pass, the dendritic microstructure of cast Al has been distorted by the shear stress developed during deformation. The processing by different routeswith number of passes has further refined the microstructure leading to a better hardness in the cast Al. © 2020 Author(s).Item Local stress and strain variations in the deformation zone can be ascertained by measuring hardness. Hardness is correlated with strain and stress. The expressions discussed later are useful in determining the local variations in stress and strain from hardness measurement. It is a simple method compared to visioplasticity. One can estimate the forces required for a forming process. It helps in the choice of equipment, design of tooling and selection of lubricant for the particular process.(Indian Academy of Sciences, Hardness-stress-strain correlation in aluminium - A simpler alternative to visioplasticity in metal forming) Dharmaveera, N.; Srinivasan, K.1996Item Heat transfer at the metal/chill interface during solidification of commercially pure aluminium square bar castings with cast iron chill at one end was investigated. Experiments were carried out for different chill thicknesses and superheats. The inner surface temperature of the chill initially was found to increase at a faster rate for higher superheats. The effect of chill thickness on the inner surface temperature of the chill was observed only after the heat from the solidifying casting had sufficient time to diffuse to the interior of the chill material. Inverse analysis of the non-linear one-dimensional Fourier heat conduction equation indicated the occurrence of peak heat flux at the end of filling of the mould. The effect of superheat on heat flux was minimal after filling. However, the effect of chill thickness had a significant effect on the heat flux after the occurrence of peak heat flux. Higher heat flux transients were estimated for castings poured at higher superheats. The corresponding heat transfer coefficients were also estimated and reported. The heat flux model presented in this work can be used for determination of casting/chill interfacial heat flux as a function of chill thickness and superheat. These heat flux transients could be used as boundary conditions during numerical simulation of solidification of the casting. © 2002 Elsevier Science B.V. All rights reserved.(Effect of chill thickness and superheat on casting/chill interfacial heat transfer during solidification of commercially pure aluminium) Gafur, M.A.; Haque, M.N.; Prabhu, K.2003Item SiC particulate reinforced A356 Al metal matrix composites were laser treated using pulsed Nd-YAG laser beam. The processing was carried out in air atmosphere at varying pulse energy (5 to 20 J) and scan rates (30 to 150 mm/sec). The samples were cut perpendicular to the track and they were characterized using optical microscopy, scanning electron microscopy and X-ray diffraction. Microstructure of laser treated region consists of regular succession of coarse and fine microstructure signifying the presence of low velocity bands. Transition from cellular/columnar dendritic to equiaxed dendritic structure has been observed. Microstructure of samples laser treated with specific energy greater than 13 kJ/cm2 show presence of Al 4C3 platelets. © 2004 Kluwer Academic Publishers.(Microstructural studies in low specific energy laser surface treated Al(A356)-SiCp composites) Bhat, K.U.; Surappa, M.K.2004Item Characterization of thin film Al/p-CdTe schottky diode(2008) Mahesha, M.G.; Kasturi, V.B.; Shivakumar, G.K.A study has been made on the behavior of Al/p-CdTe thin film junction grown by thermal evaporation method. I-V characteristics show that the Al makes Schottky contact with p-CdTe. The variation of junction capacitance with frequency and voltage has been studied to evaluate the barrier height. The activation energy and band gap have been estimated by studying variation of resistivity with temperature. Using all these data, band diagram of Al/p-CdTe has been proposed. © TÜB?TAK.Item Phase transformation, structural evolution, and mechanical property of nanostructured feal as a result of mechanical alloying(Springer New York LLC barbara.b.bertram@gsk.com, 2009) Rajath Hegde, M.M.R.; Surendranathan, A.O.The objective of the work is to synthesize nanostructured FeAl alloy powder by mechanical alloying (MEA). The work concentrates on the synthesis, characterization, and structural and mechanical properties of the alloy. Nanostructured FeAl intermetallics are prepared directly by MEA in a high-energy ball mill. Milling is performed under toluene solution to avoid contamination from the milling media and atmosphere. Mixtures of elemental Fe and Al are progressively transformed into a partially disordered solid solution with an average composition of Fe-50 at.% Al. Phase transformation, structural changes, morphology, particle size measurement, and chemical composition during MEA are investigated by X ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDS). Vickers microhardness (VMH) indentation tests are performed on the powders. The XRD and SEM studies reveal the alloying of elemental powders as well as transition to nanostructured alloy; crystallite size of 18 nm is obtained after 28 h of milling. Expansion/contraction in lattice parameter accompanied by reduction in crystallite size occurs during transition to nanostructured alloy. Longer milling introduces ordering in the alloyed powders as proved by the presence of superlattice reflection. Elemental and alloyed phases coexist while hardness increases during MEA. copy2009 Springer Science+Business Media, Inc.Item Thermal contact at solder/substrate interfaces during solidification(2009) Nyamannavar, S.; Prabhu, K.N.Heat flux transients at the solder/substrate interface during the solidification of Sn-37Pb and Sn-3.5Ag solder alloys against metallic substrates were estimated by the lumped heat capacitance model and the contact condition was assessed by scanning electronic microscopy (SEM). Copper substrates yielded maximum contact heat flux followed by brass and aluminium substrates. The SEM study in the solder/substrate interfacial region revealed the existence of a clear gap with the aluminium substrate. A conforming contact was obtained with copper and brass substrates. © 2009 Institute of Materials, Minerals and Mining.Item Finite element analysis of open die extrusion of al-5zn-1mg alloy; Analiza izguravanja legure al-5zn-1mg kroz otvoreni kalup pomo]u kon?nih elemenata(2009) Geethalakshmi, K.; Srinivasan, K.In this work, an effort has been made to study the open die extrusion of Al-5Zn-1Mg alloy using finite element analysis. The two basic parameters of open die extrusion, i.e., die included angle and the extrusion strain are varied to find the corresponding limiting strain values. Effect of main parameters on the open die extrusion is analyzed, and the limiting range of deformation is obtained. The results obtained are verified by means of contrasting with the experimental data. Pure open die extrusion is found to be possible for extrusion strain (relative strain during extrusion) up to 0.28. However, as the extrusion strain increases from 0.09 to 0.28, upsetting dominates over pure extrusion on varying the die angle from 12° to 40°.