1. Faculty Publications
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Item Wetting behaviour and interfacial microstructure of Sn-Ag-Zn solder alloys on nickel coated aluminium substrates(2011) Satyanarayan; Prabhu, K.N.Wetting behaviours of two lead free solders (Sn-2�625Ag- 2�25Zn and Sn-1�75Ag-4�5Zn) on nickel coated aluminium substrates were investigated. Sn-2�625Ag-2�25Zn exhibited better wettability compared to Sn-1�75Ag-4�5Zn solder. Contact angles of the solders increased with increasing roughness of the substrate. The Young-Dupre equation was used to evaluate the work of adhesion of solder on the substrate. Sn-2�625Ag-2�25Zn solder exhibited higher work of adhesion than Sn-1�75Ag-4�5Zn. A thin continuous layer of Ni 3Sn was detected at the interface between Sn-2�625Ag- 2�25Zn solder and nickel coated Al substrate. Sn-1�75Ag- 4�5Zn solder exhibited scallop intermetallic compounds (IMCs) growing into the solder field as well as a thin continuous IMC in some cases. Ni 3Sn and Ni3Sn4 IMCs were observed at the interface of Sn-1�75Ag-4�5Zn solder and nickel coated Al. � 2011 Institute of Materials, Minerals and Mining.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 Thermal Analysis of Cerium-Treated Chill-Cast Al-23 Si Alloy(2018) Vijeesh, V.; Prabhu, K.N.The influence of elemental cerium addition on the cooling curve parameters and microstructure of hypereutectic Al-23Si alloy was investigated in this work. The cooling rate of the treated and untreated alloy samples was varied by solidifying the melt against chills of different materials in a stainless-steel tube. The cooling curve was recorded and nucleation temperatures of various phases in the alloy were measured. The results show that the chilling improves the effectiveness of the modifier. The two main phases of the alloy, primary silicon and eutectic silicon, were nucleated at temperatures of about 661.2 and 571.6 C, respectively. The addition of Ce to slowly cooled alloys resulted in an increase in undercooling temperature of both the phases, with a decrease in its nucleation temperature, whereas the same additions increased the nucleation temperatures in chilled alloys. Based on the thermal analysis results, a relation between thermal analysis parameter (? TG) and silicon particle size of the alloy was proposed. 2018, ASM International.Item The Effect of Wetting Gravity Regime on Shear Strength of SAC and Sn-Pb Solder Lap Joints(2017) Sona, M.; Prabhu, K.N.The failure of solder joints due to imposed stresses in an electronic assembly is governed by shear bond strength. In the present study, the effect of wetting gravity regime on single-lap shear strength of Sn-0.3Ag-0.7Cu and Sn-2.5Ag-0.5Cu solder alloys reflowed between bare copper substrates as well as Ni-coated Cu substrates was investigated. Samples were reflowed for 10 s, Tgz (time corresponding to the end of gravity regime) and 100 s individually and tested for single-lap shear strength. The single-lap shear test was also carried out on eutectic Sn-Pb/Cu- and Sn-Pb/Ni-coated Cu specimens to compare the shear strength values obtained with those of lead-free alloys. The eutectic Sn-Pb showed significantly higher ultimate shear strength on bare Cu substrates when compared to Sn-Ag-Cu alloys. However, SAC alloys reflowed on nickel-coated copper substrate exhibited higher shear strength when compared to eutectic Sn-Pb/Ni-coated Cu specimens. All the substrate/solder/substrate lap joint specimens that were reflowed for the time corresponding to the end of gravity regime exhibited maximum ultimate shear strength. 2017, ASM International.Item The Effect of Thermal Ageing on Solder/Substrate Interfacial Microstructures During Reflow of Sn 37Pb and Sn 3Ag 0.5Cu(2019) Satyanarayan; Kumarswamy, M.C.; Prabhu, K.N.In the current study, the influence of thermal ageing on evolution of microstructures in the interfacial region between solders (Sn 37Pb, Sn 3.5Ag 0.5Cu) and copper substrates was investigated. Pb-containing and Pb-free solders were reflowed on Cu substrates at 230 C for 15 min and were isothermally aged at 100 C for 24 h. As-reflowed Sn Pb solder/Cu substrate interfacial region exhibited continuous and layered type of IMC at the interface, and this IMC morphology changed to scallop type with isothermal ageing. SAC solder/Cu as-reflowed samples showed continuous and needle-shaped Cu6Sn5 and Ag3Sn IMCs at the interface. However, in an isothermally aged condition, plate-shaped Cu6Sn5 and flower-shaped Ag3Sn IMCs were found inside the solder matrix. Scanning electron microscopic (SEM) study showed that the thickness of Cu6Sn5 IMC was higher in reflowed Sn Pb/Cu region than in SAC/Cu region. 2019, The Indian Institute of Metals - IIM.Item Performance of MWCNT-Reinforced SAC0307/Cu Solder Joint Under Multiple Reflow Cycles(2018) Tikale, S.; Prabhu, K.N.The evolution of interfacial microstructure and its effect on shear strength under multiple reflow cycles for multi-walled carbon nanotubes (MWCNT)-reinforced Sn0.3Ag0.7Cu solder/copper joint was investigated. The melting characteristics, wettability and mechanical properties of the solder alloy were assessed. The addition of MWCNT in the range of 0.01 0.05 wt% improved the wettability, melting behaviour and mechanical strength of the SAC0307 solder alloy. The nanoparticles in small weight fraction (0.01 0.05 wt%) addition were more effective in retarding intermetallic compounds growth at the interface. Amongst all compositions studied, the SAC0307 0.05MWCNT nanocomposite showed significant improvement in the performance of SAC0307/Cu solder joint under multiple reflow condition. The nanoparticles reinforcement above 0.1 wt% of the solder alloy was ineffective in improving the solder performance due to increased clustering in the matrix. 2018, The Indian Institute of Metals - IIM.Item Quench cooling performance-hardness correlation for AISI 1045 and 1090 steels(2019) Nayak, U.V.; Prabhu, K.N.Heat transfer and microstructure evolution during quenching of AISI 1045 and 1090 steels in vegetable oils was investigated. To simulate the industrial quench heat treatment, reference probes made of medium and high carbon steels were quenched, and heat flux transients were estimated by taking into account the phase transformation. The cooling curves obtained with reference probes made from AISI 1045 and AISI 1090 steels showed kinks indicating enthalpy change accompanied with phase transformations during continuous cooling. This was reflected in the estimated heat flux curves. The section thickness effect on heat flux transients was examined by using probes of diameters 25 mm and 50 mm. The cooling rates measured at various locations across the section diameter of reference probes were related to the hardness using the quench factor technique. The heat transfer characteristics of the quench media, the evolved microstructure, and the resulting hardness were in complete agreement. 2019 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.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 New polypropylene supported chitosan NF-membrane for desalination application(2011) Padaki, M.; Isloor, A.M.; Fernandes, J.; Prabhu, K.N.In the present study, a new NF membrane was prepared by coating chitosan on polypropylene fiber support, by the dissolution of chitosan in 2% acetic acid solution. The resulting membrane was characterized by thermo gravimetric analysis, water absorption, contact angle measurement and scanning electron microscopy. Prepared membrane showed two Tg peaks, one at ~90 C that was due to chitosan and the other peak at ~170 C that was corresponding to the supporting polypropylene membrane. The membrane showed a low swelling ratio at pH 7, 9, and 11 as compared with pH 5. The performance of the membrane was assessed out using dead end cell. Water flux was studied at different pressures. The salt rejection study was done using NaCl solution and the effect of pH on performance of the membrane was also examined. Newly prepared membrane showed improved water flux, and % of rejection is highest in acidic pH and lowest in basic pH. Hydrulic permeability coefficient and the dielectric constant confirms that the prepared membrane is nanofiltration membrane. 2011 Elsevier B.V.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.