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Item Two Parameter Weibull Analysis of the Effect of Chemical Modification of Al�7si�0.3�Mg Alloy on Ultimate Tensile Strength(2014) Raghunathan, R.; Prabhu, K.N.; Hegde, T.G.Double oxide films are one of the primary reasons that cause casting defects particularly in dross forming alloys. It is not clear whether the beneficial effect of modification melt treatment in Al�Si alloys is entirely due to the transformation of acicular eutectic Si to fibrous morphology. In the present work, the effect of chemical modification of Al�7Si�0.3�Mg alloy on casting reliability was assessed from the Weibull analysis of tensile strengths. The findings show that the modification melt treatment of Al�Si alloy has a beneficial effect as indicated by consistently higher Weibull modulus. Apart from transformation in the silicon morphology, modifiers decrease the scatter present as a result of various defects, particularly the bi-film, resulting in higher reliability for the modified castings. � 2014, The Indian Institute of Metals - IIM.Item Wetting kinetics, kinematics and heat transfer characteristics of pongamia pinnata vegetable oil for industrial heat treatment(2014) Ramesh, G.; Prabhu, K.N.The suitability of pongamia pinnata vegetable oil as cooling medium for quench heat treatment was investigated. Wetting kinetics, kinematics and heat transfer characteristics of pongamia oil during immersion quenching of hot Inconel probe were determined and compared with palm and mineral oils. A comparison of the relaxation of contact angle indicated early attainment of equilibrium contact angle for pongamia oil droplet on Inconel substrate. The equilibrium contact angle value of pongamia oil was in between mineral and palm oils. However, the spreading kinetics was faster with pongamia oil. Pongamia oil showed the formation of a stable vapour film on the probe surface during quenching. This phenomenon was not observed in palm oil and other vegetable oils reported in literature. Pongamia pinnata oil exhibits uniform nature of wetting front, intermediate rewetting temperature and less variations in rewetting temperatures during quenching. The hardening power of pongamia oil was higher than palm and mineral oils and the cooling of the probe was more uniform during quenching in pongamia oil. The heat transfer characteristics of pongamia oil were found to be superior to palm and mineral oils after film/transition boiling. Pongamia oil showed lower heat transfer but more uniform cooling during film boiling. � 2014 Elsevier B.V.Item Wetting behavior of solders(2010) Kumar, G.; Prabhu, K.N.Lead bearing solders have been used extensively in the assembly of modern electronic circuits. However, increasing environmental and health concerns about the toxicity of lead has led to the development of lead-free solders. Wetting of solders on surfaces is a complex and important phenomenon that affects the interfacial microstructure and hence the reliability of a solder joint. The solder material reacts with a small amount of the base metal and wets the metal by intermetallic compound (IMC) formation. The degree and rate of wetting are the two important parameters that characterize the wetting phenomenon. Contact angle is a measure of the degree of wetting or wettability of a surface by a liquid. Spreading kinetics in a given system is strongly affected by the experimental conditions. In reactive systems like soldering, wetting and chemical interfacial reactions are interrelated, and hence for successful modeling, it is essential to assess the effect of interfacial reactions on kinetics of wetting. Solder wetting necessarily involves the metallurgical reactions between the filler metal and the base metal. This interaction at the solder/base metal interface results in the formation of IMCs. During soldering an additional driving force besides the imbalance in interfacial energies originates from the interfacial reactions. The formation of IMC has significant influence on contact angle. The presence of IMCs (thin, continuous, and uniform layer) between solders and substrate metals is an essential requirement for good bonding. Optimum thickness of an IMC layer offers better wettability and an excellent solder joint reliability. However, due to their inherent brittle nature and tendency to generate structural defects, a too thick IMC layer at the interface may degrade the joint. In this paper, the factors affecting the wetting behavior of solders and evolution of interfacial microstructure are reviewed and discussed. Copyright � 2010 by ASTM International.Item Wetting behaviour and evolution of microstructure of Sn-Ag-Zn solders on copper substrates with different surface textures(2011) Satyanarayan; Prabhu, K.N.The effect of surface roughness on wetting behaviour and evolution of microstructure of two lead-free solders (Sn-2.625Ag-2.25Zn and Sn-1.75Ag-4.5Zn) on copper substrate was investigated. Both solders exhibited good wettability on copper substrates having rough surface and lower wettabilty on smooth surfaces. The contact angles of solders decreased linearly with increase in surface roughness of the substrate. The exponential power law, ?=exp(-KT -1), was used to model the relaxation behaviour of solders. A high intermetallic growth was observed at the interface particularly on copper substrates with rough surface texture. A thin continuous interface showing scallop intermetallic compounds (IMC) was obtained on smooth surfaces. With an increase in surface roughness, the IMC morphology changed from scallop shaped to needle type at the Sn-2.625Ag-2.25Zn solder/ substrate interface and nodular to plate like IMCs for Sn-1.75Ag-4.5Zn solder matrix. Copyright � 2010 by ASTM International.Item Wetting behaviour and evolution of microstructure of Sn-Ag-Zn solders on copper substrates with different surface textures(2010) Satyanarayan; Prabhu, K.N.The effect of surface roughness on wetting behaviour and evolution of microstructure of two lead-free solders (Sn-2.625Ag-2.25Zn and Sn-1.75Ag-4.5Zn) on copper substrate was investigated. Both solders exhibited good wettability on copper substrates having rough surface and lower wettabilty on smooth surfaces. The contact angles of solders decreased linearly with increase in surface roughness of the substrate. The exponential power law, ?=exp(-K ?n), was used to model the relaxation behaviour of solders. A high intermetallic growth was observed at the interface particularly on copper substrates with rough surface texture. A thin continuous interface showing scallop intermetallic compounds (IMC) was obtained on smooth surfaces. With an increase in surface roughness, the IMC morphology changed from scallop shaped to needle type at the Sn-2.625Ag-2.25Zn solder/substrate interface and nodular to plate like IMCs for Sn-1.75Ag-4.5Zn solder matrix. Copyright � 2010 by ASTM International.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 Wetting kinematics and spreading behaviour of water based aluminium nanofluids during immersion quenching(2013) Ramesh, G.; Prabhu, K.N.In the present work, wetting kinematics of water based aluminium nanofluids having nanoparticle concentrations varying from 0.001 to 0.5 vol.-% during immersion quenching of Inconel 600 probe was investigated by measuring the contact resistance. The contact resistance between the quench probe and counter electrode during quenching indicated that the duration of the film of water vapour decreased with increasing nanoparticle concentration as well as absence of stable vapour film formation with 0.05, 0.1 and 0.5 vol.-% of nanoparticles. The phenomenon of a repeated wetting process was observed during quenching in nanofluids. Further, quenching in 0.1 and 0.5 vol.-% nanofluids indicated the formation of a nanoparticle porous layer and its deposition on the quench probe. The spreading behaviour was studied by measuring the dynamic contact angle of nanofluids droplets on Inconel 600 substrate. Contact angle measurement showed that the addition of aluminium nanoparticles did not have a significant effect on the relaxation of contact angle of water droplet. However, lower static contact angles were obtained for nanofluids indicating improved wetting. � 2013 IHTSE Partnership.Item Wettability of root canal sealers on intraradicular dentine treated with different irrigating solutions(2013) Ballal, N.V.; Tweeny, A.; Khechen, K.; Prabhu, K.N.; Satyanarayan; Tay, F.R.Objectives The aim of this in vitro study was to evaluate the wettability of AH Plus and ThermaSeal Plus sealers on intraradicular dentine treated with different irrigating solutions. Methods Fifty anterior teeth were decoronated and split longitudinally. Each root half was divided into 5 groups (n = 10). Group I: 5 mL of 2.5% NaOCl + QMix. Group II: 5 mL of 2.5% NaOCl + 17% EDTA. Group III: 5 mL of 2.5% NaOCl + 7% maleic acid. Group IV: 5 mL of 2.5% NaOCl. Group V: 5 mL of distilled water. Irrigation regimens were performed for 1 min. Each specimen was placed inside a Dynamic Contact Angle Analyser. A controlled-volume droplet of sealer was placed on each specimen and the static contact angle was analysed. Results The contact angle made by both sealers with EDTA-irrigated dentine was significantly larger when compared to the other irrigants (P < 0.05). For ThermaSeal Plus, contact angles produced on maleic acid-, NaOCl- and distilled water-irrigated dentine were not significantly different, but were all significantly larger than the contact angle produced on QMix-irrigated dentine (P < 0.05). For AH Plus, contact angles produced on NaOCl- and distilled water-irrigated dentine were not significantly different, but were significantly larger than those made by maleic acid and QMix. Conclusion When used as a final irrigant, QMix favours the wetting of root canal dentine by both AH Plus and ThermaSeal Plus sealers. Maleic acid shows a promising result when compared to EDTA and NaOCl. Wettability of both sealers is the worst on EDTA-irrigated dentine. Clinical significance The present study highlights the effect of newer endodontic irrigating solutions on the wettability of sealers on to the root canal dentine, which is required for obtaining good obturation seal. � 2013 Elsevier Ltd.Item Wetting behavior of solders(2011) Kumar, G.; Prabhu, K.N.Lead bearing solders have been used extensively in the assembly of modern electronic circuits. However, increasing environmental and health concerns about the toxicity of lead has led to the development of lead-free solders. Wetting of solders on surfaces is a complex and important phenomenon that affects the interfacial microstructure and hence the reliability of a solder joint. The solder material reacts with a small amount of the base metal and wets the metal by intermetallic compound (IMC) formation. The degree and rate of wetting are the two important parameters that characterize the wetting phenomenon. Contact angle is a measure of the degree of wetting or wettability of a surface by a liquid. Spreading kinetics in a given system is strongly affected by the experimental conditions. In reactive systems like soldering, wetting and chemical interfacial reactions are interrelated, and hence for successful modeling, it is essential to assess the effect of interfacial reactions on kinetics of wetting. Solder wetting necessarily involves the metallurgical reactions between the filler metal and the base metal. This interaction at the solder/base metal interface results in the formation of IMCs. During soldering an additional driving force besides the imbalance in interfacial energies originates from the interfacial reactions. The formation of IMC has significant influence on contact angle. The presence of IMCs (thin, continuous, and uniform layer) between solders and substrate metals is an essential requirement for good bonding. Optimum thickness of an IMC layer offers better wettability and an excellent solder joint reliability. However, due to their inherent brittle nature and tendency to generate structural defects, a too thick IMC layer at the interface may degrade the joint. In this paper, the factors affecting the wetting behavior of solders and evolution of interfacial microstructure are reviewed and discussed. Copyright � 2010 by ASTM International.Item Wetting and cooling performance of mineral oils for quench heat treatment of steels(2014) Ramesh, G.; Prabhu, K.N.In the present work, wetting kinetics, kinematics and heat transfer characteristics of mineral oils having varying thermo-physical properties sourced from different suppliers were investigated using contact angle, online video imaging and cooling curve analysis techniques. The relaxation behavior of mineral oils of low viscosity and surface tension on Inconel substrate indicated improved wettability and fast spreading kinetics while mineral oils of high viscosity and surface tension showed reduced wettability and slower spreading kinetics. Further, the spreading behavior of mineral oils of lower viscosity and density showed the absence of viscous regime. During rewetting, formation of double wetting fronts and more uniform nature of wetting front were observed with mineral oils of high viscosity and flash point whereas no additional wetting front was observed for mineral oils of low viscosity and flash point. Among the convectional/fast/hot mineral oils, higher wetting front velocity and cooling rate were obtained for low viscosity mineral oil. The heat extracting capability of high viscosity mineral oils was higher during vapour and nucleate boiling and lower during liquid cooling stage. Further, highly viscous mineral oils showed uniform heat transfer compared to mineral oils having low viscosity. � 2014 ISIJ.