Journal Articles
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Item Casting/mould interfacial heat transfer during solidification in graphite, steel and graphite lined steel moulds(Maney Publishing maney@maney.co.uk, 2003) Prabhu, K.; Mounesh, H.; Suresh, K.M.; Ashish, A.A.Heat flow between the casting and the mould during solidification of three commercially pure metals, in graphite, steel and graphite lined steel moulds, was assessed using an inverse modelling technique. The analysis yielded the interfacial heat flux (q), heat transfer coefficient (h) and the surface temperatures of the casting and the mould during solidification of the casting. The peak heat flux was incorporated as a dimensionless number and modeled as a function of the thermal diffusivities of the casting and the mould materials. Heat flux transients were normalised with respect to the peak heat flux and modeled as a function of time. The heat flux model proposed was used to estimate the heat flux transients during solidification in graphite lined copper composite moulds.Item Review on microstructure evolution in Sn-Ag-Cu solders and its effect on mechanical integrity of solder joints(2013) Sona, M.; Prabhu, K.The use of Pb-bearing solders in electronic assemblies is avoided in many countries due to the inherent toxicity and environmental risks associated with lead. Although a number of "Pb-free" alloys have been invented, none of them meet all the standards generally satisfied by a conventional Pb-Sn alloy. A large number of reliability problems still exist with lead free solder joints. Solder joint reliability depends on mechanical strength, fatigue resistance, hardness, coefficient of thermal expansion which are influenced by the microstructure, type and morphology of inter metallic compounds (IMC). In recent years, Sn rich solders have been considered as suitable replacement for Pb bearing solders. The objective of this review is to study the evolution of microstructural phases in commonly used lead free xSn-yAg-zCu solders and the various factors such as substrate, minor alloying, mechanical and thermo-mechanical strains which affect the microstructure. A complete understanding of the mechanisms that determine the formation and growth of interfacial IMCs is essential for developing solder joints with high reliability. The data available in the open literature have been reviewed and discussed. © 2013 Springer Science+Business Media New York.Item Review of microstructure evolution in hypereutectic Al-Si alloys and its effect on wear properties(2014) Vijayan, V.; Prabhu, K.Al-Si alloys with silicon content more than 13 % are termed as hypereutectic alloys. In recent years, these alloys have drawn the attention of researchers due to their ability to replace cast iron parts in the transportation industry. The properties of the hypereutectic alloy are greatly dependent on the morphology, size and distribution of primary silicon crystals in the alloy. Mechanical properties of the hypereutectic Al-Si alloy can be improved by the simultaneous refinement and modification of the primary and eutectic silicon and by controlling the solidification parameters. In this paper, the effect of solidification rate and melt treatment on the evolution of microstructure in hypereutectic Al-Si alloys are reviewed. Different types of primary silicon morphology and the conditions for its nucleation and growth are explained. The paper discusses the effect of refinement/modification treatments on the microstructure and properties of the hypereutectic Al-Si alloy. The importance and effect of processing variables and phosphorus refinement on the silicon morphology and wear properties of the alloy is highlighted. © 2013 Indian Institute of Metals.Item Heat transfer at the casting/chill interface during solidification of Al-11 % Si eutectic alloy (LM 6) was investigated. Experiments were carried out for various combinations of chill thickness, casting height and chill material. The thermal history at nodal locations in the chill was used to estimate the interfacial heat flux by inverse modelling. A new parameter called the heat flux penetration time was proposed to model the transformation of the interfacial condition from a perfect contact to a nonconforming contact. The heat transfer coefficient was modelled as a function of the chill thickness, casting height and the thermal diffusivity of the chill material. Real time x-ray imaging technique was adopted to observe the casting/chill interface during solidification of the alloy. The video pictures indicate that a gas gap forms in the case of thin chills. The formation of the gap in thick chills could not be detected. The widths of the gap formed at the interface were measured by an image analyser which revealed that the width of the gap not only varies with time but also with position along the chill surface.(Maney Publishing michael.wagreich@univie.ac.at, Investigation of casting/chill interfacial heat transfer during solidification of Al-11% Si alloy by inverse modelling and real-time x-ray imaging) Prabhu, K.; Campbell, J.1999Item Item During soldering, the solder/substrate thermal contact conductance must be high enough to prevent the separation of the solidified shell from the substrate. In the present work, the effect of thermal contact conductance on temperature distribution inside a 60Sn-40Pb solder alloy solidifying against metallic chills was simulated. The results of the simulation indicated that the thermal contact conductance plays a major role during solidification in the solder/substrate interfacial region of the casting particularly when the substrate material has a high thermal conductivity. The influence of solder/chill contact conductance on solidification decreased with increase in the distance from the solder/chill interface.(Effect of thermal contact conductance on the solidification of a Pb-Sn solder alloy) Prabhu, K.; Kumar, S.T.; Venkataraman, N.2002Item 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.2003