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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 Metal/quenchant interfacial heat flux transients during quenching in conventional quench media and vegetable oils(2003) Prabhu, K.N.; Prasad, A.The determination of quench severity and the quantification of the boundary conditions at the metal/quenchant interface would be of considerable utility to the heat treating community. In the present work, an attempt has been made to determine the quench severity of various quench media including three vegetable oils, by the Grossmann Hardenability Factor method and by estimation of heat flux transients by inverse modeling of heat conduction in 304 stainless steel quench probes. The heat flux transient technique was found to be more accurate than the Grossmann technique in assessing the severity of quenching. This finding was supported by the hardness data and microstructure @@@ with the quenched steel specimens. New heat flux parameters are proposed to assess the severity of quenching. The boundary heat flux transients during end quenching of AISI 1040 steel specimens were also estimated. The estimated heat flux transients could be used for modeling of heat transfer during quenching. An attempt has also been made in the present work to assess the feasibility of three vegetable oils, namely coconut, sunflower, and groundnut oils, as quenching media. Further investigation is required in this direction to explore the suitability of these oils for industrial heat treating applications. This application would have immense environmental and economical benefits.Item Nanoquenchants for industrial heat treatment(2008) Prabhu, K.N.; Fernades, P.The present work outlines the possibility of using nanofluids for industrial heat treatment. Development of nanoquenchants having (i) high quench severity for enhancement of heat transfer for thick sections with low quench sensitivity and (ii) low cooling severity for thin sections with high quench sensitivity would be extremely useful to the heat treating community. The temperature dependent heat transfer coefficient and the wettability of the medium are the two important parameters that can be used to characterize a nanoquenchant to assess its suitability for industrial heat treatment. 2007 ASM International.Item Modification of eutectic silicon in Al-Si alloys(2008) Hegde, S.; Prabhu, K.N.The mechanical properties of Al-Si alloys are strongly related to the size, shape and distribution of eutectic silicon present in the microstructure In order to improve mechanical properties, these alloys are generally subjected to modification melt treatment, which transforms the acicular silicon morphology to fibrous one resulting in a noticeable improvement in elongation and strength. Improper melt treatment procedures, fading and poisoning of modifiers often result in the structure which is far from the desired one. Hence it is essential to assess the effectiveness of melt treatment before pouring. A much investigated reliable thermal analysis technique is generally used for this purpose. The deviation from the standard curve in thermal analysis helps in assessing the level of refinement of the Si structure. In the present review an attempt is made to discuss various aspects of modification, including mechanism, interaction of defects and non-destructive assessment by thermal analysis. 2008 Springer Science+Business Media, LLC.Item Heat flux transients at the solder/substrate interface in dip soldering(2008) Nyamannavar, S.; Prabhu, K.N.In the present work an experimental set-up was designed to simulate the dip soldering conditions. The set-up was used to estimate heat flux transients at the solder/substrate interface during solidification of Sn 3.5Ag solder against copper substrate. The inverse heat conduction problem (IHCP) was solved in the substrate region for estimation of heat flux transients. A reasonably good agreement between measurements and model predictions was achieved validating the inverse model. The computer code developed in the present study could be used to assess the effect of process variables on contact heat flux at the solder/substrate interface.Item Heat flux transients at the casting/chill interface during solidification of aluminum base alloys(1991) Kumar, T.S.P.; Prabhu, K.N.Heat flow at the metal/chill interface of bar-type castings of aluminum base alloys was modeled as a function of thermophysical properties of the chill material and its thickness. Experimental setup for casting square bars of Al-13.2 pct Si eutectic and Al-3 pet Cu-4.5 pct Si long freezing range alloys with chill at one end exposed to ambient conditions was fabricated. Experiments were carried out for different metal/chill combinations with and without coatings. The thermal history at nodal locations in the chill obtained during the experiments was used to estimate the interface heat flux by solving a one-dimensional Fourier heat conduction equation inversely. Using the data on transient heat flux q, the heat flow at the casting/chill interface was modeled in two steps: (1) The peak in the heat flux curve qmax was modeled as a power function of the ratio of the chill thickness d to its thermal diffusivity a, and (2) the factor (q/qmax) X ?0.05 was also modeled as a power function of the time after the solidification set in. The model was validated for Cu-10 pct Sn -2 pct Zn alloy chill and Al-13.2 pct Si and Al-3 pct Cu-4.5 pct Si as the casting alloys. The heat flux values estimated using the model were used as one of the boundary conditions for solidification simulation of the test casting. The experimental and simulated temperature distributions inside the casting were found to be in good agreement. 1991 The Minerals, Metals & Material Society.Item Investigation into creep behaviour of Sn-40%Pb alloy using impression creep method(2009) Prasanna, H.U.; Udupa, K.R.; Prabhu, K.N.The creep behaviour of Sn-40%Pb hypereutectic alloys cast in the molds made of different materials was investigated using impression creep technique in the temperature range from zero to 32 C and under the punching stress of 50 MPa. The creep curves.ie, profiles of indentation depth against time are generated and steady state creep rates (SSCRs) are determined. Activation energy was calculated knowing creep rates at different temperature levels. Standard metallographic technique was used to determine the grain size of alloys which were poured into different molds. It was found that SSCR, at all the temperature levels of testing, is a function of grain size of the material. The activation energy being in the range of 10kJ/mol -12 kJ/mol, suggests that the probable creep mechanism is dislocation glide aided by vacancy diffusion. Results of the experiments are discussed.Item Heat transfer during quenching of modified and unmodified gravity die-cast A357 cylindrical bars(2006) Prabhu, K.N.; 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 Heat transfer at the metal/substrate interface during solidification of Pb-Sn solder alloys(2002) Prabhu, K.N.; Kumar, S.T.; Venkataraman, N.Heat transfer analysis during the solidification of lead, tin, and two lead-base solder alloys against two different chill materials (steel and copper) was carried out with and without flux coating on the chill surface. Temperatures at two known locations inside the chill and casting were recorded as the casting started solidifying, and the acquired chill temperature data were used for solving a one-dimensional heat conduction equation inversely to yield the metal/chill interfacial heat flux and chill surface temperature as a function of time. The initial heat flux was high due to good contact at the metal/chill interface. As the casting started solidifying, there was a reduction in the heat flux due to the nonconforming contact at the interface. Chills with flux coating resulted in finer microstructures near the solder/substrate interface compared to those obtained with uncoated chills. The fineness of the microstructure also increased when copper was used as the chill material. The estimated total heat flow was found to be higher with flux-coated and copper chills. This was in good agreement with the finer microstructures obtained near the solder/chill interfacial region for solidification against copper chills and chills withflux coating on their surface.Item Heat transfer and solidification behaviour of modified A357 alloy(2007) Kumar, G.; Hegde, S.; Prabhu, K.N.Al-Si alloys are subjected to melt treatment like modification to improve their mechanical properties. Non-destructive technique like thermal analysis is generally used to assess the effectiveness of melt treatment. In the present study, the behaviour of the melt treated Al-7Si-Mg alloy (A357) during solidification with or without chilling was investigated using thermal analysis. Thermal analysis and heat transfer parameters were determined. Thermal analysis parameters were affected significantly by modification and chilling. Modification treatment resulted in the increase of cooling rate, heat evolved, casting/mould interfacial heat flux and eutectic growth velocity. A theoretical model based on undercooling from the equilibrium temperature during eutectic solidification was used to predict growth velocities and eutectic grain size. The eutectic grain sizes estimated using the model and those measured from casting microstructures were found to be in good agreement. 2006 Elsevier B.V. All rights reserved.
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