Faculty Publications
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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 Plasma-sprayed graphene oxide reinforced alumina composite coatings on low carbon steel with improved fracture toughness, brittleness index, and microhardness(Elsevier Ltd, 2020) Amudha, A.; Nagaraja, H.S.; Shashikala, H.D.In this work, the mechanical properties of atmospheric plasma-sprayed Al2O3and Al2O3-xGO (x = 0.5, 1.0, 1.5, and 2.0 wt%) coatings on low carbon steel was evaluated using the Vickers indentation technique, and the effects of GO addition in microhardness brittleness index and fracture toughness were investigated. The Fourier-transform infrared (FTIR) spectroscopy and Field Emission Scanning Electron Microscopy (FE-SEM) techniques were employed to analyze the microstructural characterization of the plasma-sprayed coatings and to confirm the retention of GO in the Al2O3-xGO composite after the plasma spray. It was found that the Vicker's microhardness of as-sprayed Al2O3is 4.148 GPa and it decreased with the increase in the addition of GO and for Al2O3-2.0GO, it is 3.305 GPa. The fracture toughness of Al2O3is 4.86 (MPa m1/2) whereas for Al2O3-2.0GO is 16.85 (MPa m1/2). The fracture toughness has increased whereas the brittleness index has decreased as the weight percentage of GO addition is increased in the Al2O3-GO composite. Thus, the plasma-sprayed Al2O3and Al2O3-xGO coatings suggest that 2 wt% GO addition helps in the improvement of brittleness, fracture toughness, and the microhardness. © 2020 Elsevier Ltd. All rights reserved.Item Sodium ion incorporated alumina - A versatile anisotropic ceramic(Elsevier Ltd, 2019) Pujar, P.; Gupta, B.; Sengupta, P.; Gupta, D.; Mandal, S.The present article is a review of crystal structure dependent anisotropic properties of β and β″-phases of sodium ion incorporated alumina. The anisotropy in electrical properties such as ionic conductivity and dielectric permittivity is due to the layered structure. Conducting plane between two consecutive spinel aluminas constituting loosely bound mobile sodium ions, promote ionic conductivity in the parallel direction. In contrary, the restricted movement of ions in the orthogonal direction brings about polarization giving it directional dielectric property. High ionic conductivity of 1.3 S/cm and large dielectric constant of ˜ 200 are reported. Exchanging sodium ions with different cations, such as potassium and lithium, results in similar anisotropy. The processing of β and β″-phases along with metastability of intermediate mullite phase is described in the current review. In addition, the applications of sodium ion incorporated aluminas, such as solid electrolyte in batteries, thin film transistors and gas sensors are discussed. © 2019 Elsevier LtdItem The precipitation hardening of a Al-Zn-Mg-Al2O3(p) composite is explored. It is found that the peak hardness achieved is almost double that of precipitation hardening of Al-Zn-Mg alloy or dispersion strengthening of Al-Zn-Mg with 5% Al2O3(p). Toughness is marginally improved and tensile strength is one and half times that of precipitation hardened Al-Zn-Mg alloys. The ageing time for peak hardness is reduced due to acceleration of formation of precipitate. © Indian Academy of Sciences.(Indian Academy of Sciences, Precipitation hardening in Al-Zn-Mg-Al2O3(p) composite) Kiran, K.S.; Srinivasan, K.1999Item Heat flow at the casting/mold interface was assessed and studied during solidification of Al-Cu-Si (LM 21) alloy in preheated cast iron molds of two different thicknesses, coated with graphite and alumina based dressings. The casting and the mold were instrumented with thermocouples connected to a computer controlled temperature data acquisition system. The thermal history at nodal locations in the mold and casting obtained during experimentation was used to estimate the heat flux by solving the one-dimensional inverse heat conduction problem. The cooling rate and solidification time were measured using the computer-aided cooling curve analysis data. The estimated heat flux transients showed a peak due to the formation of a stable solid shell, which has a higher thermal conductivity compared with the liquid metal in contact with the mold wall prior to the occurrence of the peak. The high values of heat flux transients obtained with thin molds were attributed to mold distortion due to thermal stresses. For thin molds, assumption of Newtonian heating yielded reliable interfacial heat transfer coefficients as compared with one-dimensional inverse modeling. The time of occurrence of peak heat flux increased with a decrease in the mold wall thickness and increase in the casting thickness. © ASM International.(Casting/mold thermal contact heat transfer during solidification of Al-Cu-Si alloy (LM 21) plates in thick and thin molds) Prabhu, K.; Chowdary, B.; Venkataraman, N.2005Item Optimization of electrophoretic deposition of alumina onto steel substrates from its suspension in iso-propanol using statistical design of experiments(2008) Mohanty, G.; Besra, L.; Bhattacharjee, S.; Singh, B.P.Statistical design of experiments was used to investigate the effect the process parameters on electrophoretic deposition (EPD) of alumina onto steel substrates from its suspension in iso-propanol. The process parameters considered were (i) concentration of particles in the suspension (solid loading), (ii) electrode separation, (iii) applied potential, and (iv) deposition time on the quantity of ceramic particles electrophoretically deposited. A 24 full factorial matrix, with four repetitions of the center point, was used to develop the predictive regression equation for deposition of alumina per unit area of the electrode in the design space. The results show that particle concentration has the most dominant effect with more than 50% contribution to the deposited amount. A good correlation was obtained between predicted and experimental values suggesting that the model can predict data accurately in the experimental matrix. © 2007 Elsevier Ltd. All rights reserved.Item Role of surface roughness in pool boiling with Alumina-water nanofluid on a horizontal wire surface(International Information and Engineering Technology Association, 2011) Hegde, R.N.; Rao, S.S.; Reddy, R.P.Boiling heat transfer is one of the major phenomenon which of late, has drawn the attention of many researchers and scientists throughout the world. With nanofluids, further boost is given in heat transfer enhancement. This research paper is the study of heat transfer enhancement using Alumina nanofluid in different volume concentrations ranging from 1 to 9%. The role of surface roughness on critical heat flux enhancement (CHF) in pool boiling with nanofluids was experimentally studied using a 36 gauge NiCr wire at atmospheric pressure. Experimentation included i) investigations on boiling heat transfer subjecting the wire surface to Alumina nanofluid at higher volume concentrations and ii) investigations on surface roughness due to surface coating, subjecting the wire surface to a single heating cycle with different volume concentrations of Alumina nanofluid. Boiling of nanofluid resulted in nanoparticle deposition and subsequent roughning of the wire surface. To substantiate the nanoparticle deposition and its effect on critical heat flux, investigation was done by studying the surface roughness and SEM images of the wire surface. The experimental results show the evidence of nanoparticle deposition on the wire surface and its effect on CHF enhancement and deterioration in pool boiling heat transfer.Item Quench severity and kinetics of wetting of vegetable oil blends and nanofiuid for heat treatment(2011) Jagannath, V.; Prabhu, K.N.In the present work, investigation was carried out to study the suitability of vegetable oil blends with mineral oil and alumina based nanofiuids as quench media for heat treatment. Palm oil, sunflower oil, gingili oil were blended with mineral oil in the ratio of 2:1, 3:1, 1:1, 1:2, and 1:3... Heat transfer coefficients were determined using a lumped heat capacitance model. A dynamic contact angle analyzer was used for determination of dynamic and static contact angle of the droplet on the substrate. The wetting behaviour of oils and their blends was modelled by a power law of the type: ? = ktn. Wettability of nanofiuids was found to be poor.Item Flow visualization and study of critical heat flux enhancement in pool boiling with Al2O3-water nanofluids(Serbian Society of Heat Transfer Engineers, 2012) Hegde, R.N.; Rao, S.S.; Reddy, R.P.Pool boiling heat transfer characteristics of Al2O3 -water nanofluids is studied experimentally using a NiCr test wire of 36 standard wire guage diameter. The experimental work mainly concentrated on (1) change of critical heat flux with different volume concentrations of nanofluid and (2) flow visualization of pool boiling using a fixed concentration of nanofluid at different heat flux values. The experimental work revealed an increase in critical heat flux value of around 48% andflow visualization helped in studying the pool boiling behaviour of nanofluid.Out of the various reasons which could affect the critical heatflux enhancement, surface roughness plays a major role in pool boiling heat transfer.