Journal Articles
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Item Rotating bending fatigue tests were carried out on austempered ductile iron containing 1.5 wt% nickel and 0.3 wt% molybdenum. The ductile iron was austenitized at 900 or 1050 °C and then austempered at 280 or 400 °C for different lengths of time to obtain different microstructures. The fatigue strength was correlated with the amount of retained austenite and its carbon content, which were both determined by X-ray diffraction technique. While the tensile strength decreased with increasing retained austenite content, the fatigue strength was found to increase. Carbide precipitation was found to be detrimental to fatigue strength. Lower austenitizing temperature resulted in better fatigue strength. © 1994 Chapman & Hall.(Kluwer Academic Publishers, Effect of microstructure on the fatigue strength of an austempered ductile iron) Shanmugam, P.; Prasad Rao, P.; Rajendra Udupa, K.; Venkataraman, N.1994Item Austempered ductile iron containing 0.9 Ni and 0.3 Mo and subject to low stress dry sand abrasive testing shows that wear behaviour is very sensitive to heat treatment conditions. It is concluded that large retained austenite content promotes wear resistance.(Inst of Engineers (India), Low stress dry sand abrasive wear behaviour of austempered ductile iron) Prasad Rao, P.1995Item An alloy containing 49 at.% aluminium was heat treated at different temperatures within the ? + ? two-phase field to get five different volume fractions of lamellar constituent. Creep studies were carried out on these samples at five different temperatures in the interval between 1023 and 1223 K, by impression creep technique using four levels of stresses at each temperature. For a given temperature and stress, steady state impression velocity decreased with increasing volume fraction of lamellar constituent. Activation energy for steady state creep increased linearly with lamellar content from 185 kJ/mol at 22 vol.% to 362 kJ/mol at 100 vol.%. The stress exponent was found to be around 1.2 in all the cases. The results show that a fully lamellar structure has a superior behaviour where creep is an important factor.(Carl Hanser Verlag, Effect of microstructure on the impression creep of two-phase titanium aluminide) Prasad Rao, P.; Swamy, K.Shivananda1995Item Photoconductivity has been studied in cadmium selenide thin films prepared by thermal evaporation in vacuum. Attempts have been made to correlate the photoresponse with the deposition conditions. It has been observed that as-grown films, irrespective of the cadmium content, are not photosensitive and that baking in air, especially above 723 K, leads to considerable improvement in the photoconducting properties of cadmium selenide films.(Photoconductivity in vacuum deposited cadmium selenide thin films) Rajendra, B.V.; Kasturi, V.B.; Shivakumar, G.K.2004Item Heat transfer during quenching of modified and unmodified gravity die-cast A357 cylindrical bars(2006) Prabhu, K.; Hemanna, P.Heat transfer during quenching of chill-cast modified and unmodified A357 Al-Si alloy was examined using a computer-aided cooling curve analysis. Water at 60°C and a vegetable oil (palm oil) were used as quench media. The measured temperatures inside cylindrical probes of the A357 alloy were used as inputs in an inverse heat-conduction model to estimate heat flux transients at the probe/quenchant interface and the surface temperature of the probe in contact with the quench medium. It was observed that modified alloy probes yielded higher cooling rates and heat flux transients. The investigation clearly showed that the heat transfer during quenching depends on the casting history. The increase in the cooling rate and peak heat flux was attributed to the increase in the thermal conductivity of the material on modification melt treatment owing to the change in silicon morphology. Fine and fibrous silicon particles in modified A357 probes increase the conductance of the probe resulting in higher heat transfer rates. This was confirmed by measuring the electrical conductivity of modified samples, which were found to be higher than those of unmodified samples. The ultrasound velocity in the probes decreased on modification. ©ASM International.Item Comparative study of heat transfer and wetting behaviour of conventional and bioquenchants for industrial heat treatment(2008) Fernandes, P.; Prabhu, K.N.An investigation was conducted to study the suitability of vegetable oils as bioquenchants for industrial heat treatment. The study involved the assessment of the severity of quenching and wetting behaviour of conventional and vegetable oil quench media. Quench severities of sunflower, coconut and palm oils were found to be greater than mineral oil. The quench severity of aqueous media is greater than oil media although their wettability is poor as indicated by their higher contact angles. A dimensionless contact angle parameter defined in this work is found to be a better parameter to compare the wetting behaviour with heat transfer. © 2007 Elsevier Ltd. All rights reserved.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 Effect of heat treatment on pitting corrosion resistance of 6061 Al/SiCP composite coated by the cerium oxide film in 3.5 N NaCl solution(2011) Rajasekaran, S.; Udayashankar, N.K.; Nayak, J.One of the main drawbacks of 6061 Al/SiCP composite is its poor pitting corrosion resistance in the aggressive environment containing chloride ions, such as seawater, for example. The present article deals with the investigations of effects of aging on the corrosion behavior of 6061 Al/SiCP composite and of the heat treatment on the pitting corrosion resistance of 6061 Al/SiCP composite coated by cerium oxide prepared by chemical bath technique. Potentiodynamic polarization test was used to study the corrosion behavior of cerium oxide coatings in 3. 5N NaCl solution. The microstructure of cerium oxide was examined by scanning electron microscopy (SEM) and the formed phases were identified by X-ray diffraction (XRD). The pitting corrosion resistance of the cerium oxide coating was found to be improved after heat treatment at 300°C for 30 min. © 2011 Allerton Press, Inc.Item Effect of heat treatment on structure and properties of multilayer zn-ni alloy coatings(International Association of Physical Chemists, 2013) Rao, V.R.; Hegde, A.C.; Udaya Bhat, K.Composition modulated multilayer alloy (CMMA) coatings of Zn-Ni were electrodeposited galvanostatically on mild steel (MS) for enhanced corrosion protection using single bath technique. Successive layers of Zn-Ni alloys, having alternately different composition were obtained in nanometer scale by making the cathode current to cycle between two values, called cyclic cathode current densities (CCCD’s). The coatings configuration, in terms of compositions and thicknesses were optimized, and their corrosion performances were evaluated in 5 % NaCl by electrochemical methods. The corrosion rates (CR)’s of multilayer alloy coatings were found to decrease drastically (35 times) with increase in number of layers (only up to 300 layers), compared to monolayer alloy deposited from the same bath. Surface study was carried with SEM, while XRD was used to determine metal lattice parameters, texture and phase composition of the coatings. The effect of heat treatment on surface morphology, thickness, hardness and corrosion behaviour of multilayer Zn-Ni alloy coatings were studied. The significant structural modification due to heat treatment is not accompanied by any decrease in corrosion rate. This effect is related to the formation of a less disordered lattice for multilayer Zn-Ni alloy coatings. © 2013 by the authors; licensee IAPC, Zagreb, Croatia.Item Optical, dielectric and mechanical properties of silver nanoparticle embedded calcium phosphate glass(Elsevier, 2014) Venkateswara Rao, G.V.; Shashikala, H.D.Silver nanoparticles have been embedded in 50 mol% CaO-50 mol% P 2O5 glass using melt quenching technique. The quenched glasses were heat treated at 550 °C for different durations between 10 and 50 h. The growth of silver nanoparticles in glass matrix appeared to be time dependent. FTIR spectra revealed that silver nanocluster formation had not affected the position of vibration bands of basic phosphate tetrahedral network. The Ag nanoparticle embedded glass matrix showed the red shift and broadening of the surface plasmon resonance (SPR) peak in the visible region with the increase in the duration of the heat treatment. Results showed the increase in size of the nanoparticles in glass matrix with heat treatment which was further confirmed using transmission electron microscopy and XRD. X-ray diffraction studies indicated the presence of Ag crystalline peaks along with amorphous structure on heat treatment at 550 °C for 50 h. The dielectric constant of these glasses increased as the duration of the heat treatment increased. Increase in both Vickers hardness and fracture toughness, and decrease in brittleness were observed which can be attributed to the increase in size of the nanoparticles in glass matrix. © 2014 Elsevier B.V.