Journal Articles
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Item Oxide bifilms in aluminium alloy castings - A review(2011) Gopalan, R.; Prabhu, K.N.Aluminium alloy castings are most widely used in automobile industry because of their light weight, better castability and improved properties. The liquid aluminium surface easily oxidises during melting, transferring and pouring operation which may entrain oxide films into the casting. Research work has shown that the entrainment of this surface film and formation of bifilms in castings appear to be the source of most of the casting defects leading to a significant reduction in the mechanical properties of aluminium alloy castings. In this paper, the phenomenon of formation of oxide bifilms in aluminium alloy castings, effect of these bifilms on casting properties and their assessment techniques are discussed. For enhancing the quality of casting, research should focus towards development of process techniques for healing of bifilms in liquid metal during solidification. © 2011 Institute of Materials, Minerals and Mining.Item Reactive wetting, evolution of interfacial and bulk IMCs and their effect on mechanical properties of eutectic Sn-Cu solder alloy(2011) Satyanarayan, S.; Prabhu, K.N.Lead free solders are increasingly being used in electronic applications. Eutectic Sn-Cu solder alloy is one of the most favored lead free alloys used for soldering in electronic applications. It is inexpensive and principally used in wave soldering. Wetting of liquid solder on a substrate is a case of reactive wetting and is accompanied by the formation of intermetallic compounds (IMCs) at the interface. Wettability of Sn-0.7Cu solder on metallic substrates is significantly affected by the temperature and the type of flux. The wettability and microstructural evolution of IMCs at the Sn-0.7Cu solder/substrate interfaces are reviewed in the present paper. The reliability of solder joints in electronic packaging is controlled by the type and morphology of interfacial IMCs formed between Sn-0.7Cu solder and substrates. The formation and growth mechanisms of interfacial IMCs are highlighted. Mechanical behavior of bulk solder alloy and solder joint interfaces are analyzed. The characteristics of the IMCs which have marked effect on the mechanical properties and fracture behavior as well as reliability of solder joints of the alloy are discussed. An attempt has also been made to discuss the effect of cooling rate and strain rate on shear strength, tensile properties and creep resistance of the solder alloy. It is recommended that future work should focus on evolving a standard procedure involving sequential assessment of wetting behavior, evolution of IMCs and mechanical properties. © 2011 Elsevier B.V.Item Preparation, characterization and performance study of poly(isobutylene- alt-maleic anhydride) [PIAM] and polysulfone [PSf] composite membranes before and after alkali treatment(2011) Padaki, M.; Isloor, A.M.; Belavadi, G.; Prabhu, K.N.Recently, nanofiltration (NF) membranes have been drawing much attention in the field of filtration and the purification process of water/industrial effluents, because of their energy efficiency and low cost. Although reverse osmosis (RO) membranes are widely used in present desalination units, NF membranes are considered as "future membranes" for desalination, because of the low operating pressure. In the present paper, we hereby report the synthesis of a new composite NF membranes of poly(isobutylene-alt-maleic anhydride) (PIAM) with polysulfone, using a diffusion-induced phase separation (DIPS) method. The anhydride groups were converted to acid group by alkaline treatment. Newly prepared composite membranes were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) studies. The membranes were tested for salt rejection and water swelling. The resulted NF membranes exhibited significantly enhanced water permeability while retaining high salt rejection. The flux and rejection rate of the NF membrane to Na2SO4 (500 ppm) reached to 11.73 L/(m2 h) and 49% rejection under 1 MPa and also 70:30 composition of the membrane showed 54% water swelling; contact angle measurement, ion exchange capacity, and water uptake of the membrane were recorded. © 2011 American Chemical Society.Item Heat transfer during quenching and assessment of quench severity-A review(2009) Prabhu, K.N.; Fernandes, P.In the heat treatment of steel, quenching is done to prevent ferrite or pearlite formation and allows formation of bainite and martensite. For a particular grade of steel, the effectiveness of quenching depends on the cooling characteristics of the quenching medium. The cooling rate is not a constant throughout the quenching process; instead it varies depending upon the various stages that occur during the quenching process. Knowledge of heat transfer during various stages of quenching and kinetics of wetting of the quench medium is fundamental to the understanding of the relationship between material, quench medium, microstructure, and properties. In this paper the characteristics of various quench media, the effect of process parameters on quenching, mechanisms of thermal transport, methods of assessing severity of quenching, and techniques of estimation of heat transfer coefficients are reviewed. An attempt is also made to highlight the importance of wetting kinetics of liquid media on quenching. Copyright © 2009 by ASTM International.Item Review of thermo-physical properties, wetting and heat transfer characteristics of nanofluids and their applicability in industrial quench heat treatment(2011) Ramesh, G.; Prabhu, K.N.The success of quenching process during industrial heat treatment mainly depends on the heat transfer characteristics of the quenching medium. In the case of quenching, the scope for redesigning the system or operational parameters for enhancing the heat transfer is very much limited and the emphasis should be on designing quench media with enhanced heat transfer characteristics. Recent studies on nanofluids have shown that these fluids offer improved wetting and heat transfer characteristics. Further water-based nanofluids are environment friendly as compared to mineral oil quench media. These potential advantages have led to the development of nanofluid-based quench media for heat treatment practices. In this article, thermo-physical properties, wetting and boiling heat transfer characteristics of nanofluids are reviewed and discussed. The unique thermal and heat transfer characteristics of nanofluids would be extremely useful for exploiting them as quench media for industrial heat treatment. © 2011 Ramesh and Prabhu.Item Review of non-reactive and reactive wetting of liquids on surfaces(2007) Kumar, G.; Prabhu, K.N.Wettability is a tendency for a liquid to spread on a solid substrate and is generally measured in terms of the angle (contact angle) between the tangent drawn at the triple point between the three phases (solid, liquid and vapour) and the substrate surface. A liquid spreading on a substrate with no reaction/absorption of the liquid by substrate material is known as non-reactive or inert wetting whereas the wetting process influenced by reaction between the spreading liquid and substrate material is known as reactive wetting. Young's equation gives the equilibrium contact angle in terms of interfacial tensions existing at the three-phase interface. The derivation of Young's equation is made under the assumptions of spreading of non-reactive liquid on an ideal (physically and chemically inert, smooth, homogeneous and rigid) solid, a condition that is rarely met in practical situations. Nevertheless Young's equation is the most fundamental starting point for understanding of the complex field of wetting. Reliable and reproducible measurements of contact angle from the experiments are important in order to analyze the wetting behaviour. Various methods have been developed over the years to evaluate wettability of a solid by a liquid. Among these, sessile drop and wetting balance techniques are versatile, popular and provide reliable data. Wetting is affected by large number of factors including liquid properties, substrate properties and system conditions. The effect of these factors on wettability is discussed. Thermodynamic treatment of wetting in inert systems is simple and based on free energy minimization where as that in reactive systems is quite complex. Surface energetics has to be considered while determining the driving force for spreading. Similar is the case of spreading kinetics. Inert systems follow definite flow pattern and in most cases a single function is sufficient to describe the whole kinetics. Theoretical models successfully describe the spreading in inert systems. However, it is difficult to determine the exact mechanism that controls the kinetics since reactive wetting is affected by a number of factors like interfacial reactions, diffusion of constituents, dissolution of the substrate, etc. The quantification of the effect of these interrelated factors on wettability would be useful to build a predictive model of wetting kinetics for reactive systems. © 2007 Elsevier B.V. All rights reserved.Item Thermal interface materials for cooling microelectronic systems: present status and future challenges(Springer, 2021) Pathumudy, R.D.; Prabhu, K.N.Thermal management has become a challenging aspect particularly in the field of microelectronics due to rapid miniaturization and massive scale integration. This has resulted in the generation of enormous amounts of heat that needs to be efficiently transferred from microelectronic devices to ensure longer life cycles. The efficient transfer of heat offers advantages such as achieving higher operating temperatures and prevents component failure. A device engineer has to, therefore, identify methods that would facilitate the efficient transfer of heat from the systems. The existence of an interface between the heat source and the heat sink impedes the efficient transfer of heat. Over the years, researchers have identified techniques that could be employed to reduce the interface impediments. Among these techniques, the application of thermal interface materials (TIMs) at the interface is the most promising and has become an integral part of applications where an efficient transfer of heat across interfaces is desirable. In the present paper, the assessment of contact resistance, properties of interface materials and thermal management of microelectronic devices using TIMs are discussed. The present status of TIMs is critically reviewed and the future challenges are highlighted. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Item Thermal Resistance at the Polymer/Mold Interface in Injection Molding(Springer, 2022) Kamala Nathan, D.K.; Prabhu, K.N.In injection molding, the thermomechanical condition of the solidifying part inside the cavity determines the morphology developed during cooling and thus the final properties of the component. This condition is significantly affected by the thermal contact resistance (TCR) at the polymer/mold interface. TCR is one of the most significant heat transfer characteristics that affect the quality of injection-molded components. TCR values significantly influence the simulated temperature distribution of the solidifying part inside the cavity. Using incorrect TCR values affect the accuracy of the simulated results leading to defects in the molded components. Further, the overall heat transfer during injection molding is influenced by the coolant characteristics and the thermophysical properties of the mold material. This paper gives an insight into the role of thermal transport phenomenon in the injection molding process, and particularly the importance of TCR during simulation of injection molding. © 2021, The Indian Institute of Metals - IIM.Item Residual Stress and Distortion during Quench Hardening of Steels: A Review(Springer, 2022) Samuel, A.; Prabhu, K.N.Quench hardening is a widely used heat treatment process for achieving better mechanical properties in carbon steels. However, when high quench-sensitivity steel components having thin sections are quenched, they may get distorted due to thermal and phase transformation stresses. Appropriate steps have to be taken to minimize residual stresses and distortion during quenching operation in the heat-treating industry. Many factors such as quenchant type, quench severity, quenching process variables, the geometry of the component, and material properties significantly affect the evolution of residual stresses. The heat transfer from the metal surface to the quench medium is the critical physical phenomenon that drives the microstructure evolution and residual stresses during quenching. The nonuniformity in heat transfer between the heated metal and the quench medium is the key source of residual stress development in the quenched material. Modeling and simulation of the quenching process can predict the residual stress distribution in the quenched sample and the evolution of quench cracks and component failure. Optimizing quenching process conditions and selecting appropriate quenchants minimize residual stresses and distortion. One of the requirements for improving the accuracy of simulation models is the use of reliable spatiotemporal heat transfer boundary conditions. The present review addresses the evolution of residual stresses during quenching, factors affecting residual stresses such as geometry and section thickness of the quenched part, cooling uniformity, quenchant selection, and the interrelation between heat transfer and residual stresses. The methods to minimize residual stress and distortion in quenched parts are discussed. © 2022, ASM International.Item Microstructure and Mechanical Properties of Sn-Ag-Cu Nanocomposite Solders: A Review(ASTM International, 2025) Muhammed, H.J.; Prabhu, K.N.Sn-Ag-Cu (SAC) solder alloy is the most promising lead-free solder alloy, with Sn as the principal constituent. It offers excellent solderability and mechanical properties and addresses the environmental hazards associated with Pb-Sn solders. Key factors affecting the reliability and solderability of the alloy includes wettability, microstructure evolution, intermetallic compound (IMC) growth at the solder-substrate interface, and mechanical properties. The addition of nanoparticles in low weight fractions reduce surface tension, enhances wettability, refines the microstructure, and improves mechanical properties such as shear strength, tensile strength, and microhardness. The improvement in mechanical properties is achieved by inhibiting IMC growth and strengthening the solder matrix. However, excessive nanoparticle additions can adversely affect the properties of solder joints. Despite advancements in lead-free solders, none of the alloys has fully replaced Sn–Pb solders due to challenges in controlling IMC formation during reflow processes. The present work reviews the effects of nanoparticles on the microstructure, mechanical properties, and reliability of SAC solder alloys. The ongoing research on nanocomposite solders should focus on optimizing nanoparticle additions to enhance reliability under thermal cycling and aging conditions. © © 2025 by ASTM International.