In the present work, investigation was carried out to study the suitability of vegetable oil blen... more In the present work, investigation was carried out to study the suitability of vegetable oil blends with mineral oil and alumina based nanofluida 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 behaviuor of oils and their blends was modelled by a power law of the type: θ = kt. Wettability of nanofluids was found to poor.
Heat Treat 2019: Proceedings from the 30th Heat Treating Society Conference and Exposition
The present work presents a comprehensive comparative study on the cooling performance of hot oil... more The present work presents a comprehensive comparative study on the cooling performance of hot oil and molten KNO3- NaNO2-NaNO3 eutectic mixture quench media. The study was conducted using a cylindrical Inconel probe of 16? and 60mm length. Cooling curves at different locations in the probe were acquired using thermocouples- DAQ system. The temperature data was recorded in PC and was subsequently used to calculate spatially dependent transient heat flux at the metal quenchant interface. The heat extraction mechanism in hot oil and NaNO2 eutectic mixture was different. Quench heat transfer occurred in two stages namely boiling stage and convective cooling stage during quenching in molten NaNO2 eutectic mixture. In the case of hot oil, apart from these two stages, third stage of cooling namely vapor blanket stage was observed. A detailed study was conducted to compare magnitude and uniformity of heat extraction during each stage of quenching. Molten salt offered higher cooling rate and...
Abstract The present study is focused on the development of low Ag content 99Sn-0.3Ag-0.7Cu (SAC0... more Abstract The present study is focused on the development of low Ag content 99Sn-0.3Ag-0.7Cu (SAC0307) solder alloy with Al2O3 nanoparticles reinforcement. The effects of multiple reflow cycles and the addition of Al2O3 nanoparticles in 0.01, 0.05, 0.1, 0.3 and 0.5 percentages by weight on microstructure development and mechanical strength of the solcder joint were first investigated. The addition of ceramic nanoparticles in 0.01-0.5 wt% range resulted in 15-40% increase in the wetting area and about 10-55% increase in the microhardness of the solder. The shear strength of nanoparticles reinforced SAC0307 solder joint increased by 11-53% under multiple reflow conditions. Nano-composite solder joints containing 0.01 and 0.05 wt% Al2O3 nanoparticles showed superior shear strength and improved ductility for two reflow cycles. Hence, these nano-composites were selected and tested for their performance and joint reliability. The surface mount 2220 capacitor joint assemblies with the selected nano-composites reflowed on bare copper and Ni–P coated Cu substrates were investigated. The reliability of the solder joint was assessed by determining the joint shear strength under varying temperature environments. The nano-composite with 0.05 wt% nanoparticles addition resulted in maximum joint reliability compared to monolithic solder. The Ni–P coating on the Cu substrate significantly hindered the IMC growth at the joint interface under different thermal conditions. The joint strength improved by about 26% for samples reflowed on Ni–P surface finish compared to that on bare Cu metallization. The Weibull analysis of the joint shear strength under all thermal conditions suggest that the addition of Al2O3 nanoparticles in very small amounts to SAC0307 solder and the presence of Ni–P surface finish on Cu substrate significantly enhances the performance and reliability of solder joints. In terms of both quality and reliability, the newly developed low-silver content SAC0307+0.05Al2O3 nano-composite is an effective alternate lead-free solder that can be used in microelectronics industry in place of high-silver content Sn–Ag–Cu solders.
In the present study, wettability, interfacial intermetallic growth and shear strength of Sn–Cu e... more In the present study, wettability, interfacial intermetallic growth and shear strength of Sn–Cu eutectic solder solidified on bare as well as nickel-coated copper substrates were examined. Sn–0.7Cu solder was reflowed over the substrate for reflow times ranging from 10 to 500 s at 270 °C. Samples were cooled by quenching in water. The wetting behavior was similar on both the substrates. The corresponding time period to the end of gravity zone (Tgz) was measured from the relaxation curve obtained from wetting studies. Tgz was found to be 25 s for Sn–0.7Cu on bare and 50 s on Ni-coated copper substrates. The intermetallic compound layer thickness was fitted to a growth model to study the growth kinetics. The integrity of solder/substrate joint was assessed by performing ball as well as single-lap joint shear tests. The shear strength was found to be maximum at Tgz for all solder/substrate systems.
Cooling behaviour of steels in quench media is of great importance as this controls phase transfo... more Cooling behaviour of steels in quench media is of great importance as this controls phase transformations, heat transfer and the stress evolution. The heat extraction ability of each quenchant is different because of varying thermophysical properties and wetting behaviour. The quenchants should be selected in such a way that they provide uniform cooling of steel. In the present investigation, quenching experiments were carried out with Inconel 600, EN19, EN24, EN31 steel grades in distilled water, servo oil, carbonated distilled water and 10% PAG. The cooling curve analysis of the quenching process was carried out with temperature data recorded during quenching. This measured temperature–time data were used to estimate the heat flux by inverse modelling without considering the effect of phase transformation. The crack propensity was quantified using the quench uniformity ratio. The hardness distribution observed during quenching in carbonated distilled water was observed to be more uniform compared to other quench media.
Solar energy storage technologies have proved to be promising in terms of providing uninterrupted... more Solar energy storage technologies have proved to be promising in terms of providing uninterrupted power supply. The phase change materials (PCMs) with their higher heat storage capacity are more efficient than sensible heat storage materials. In this study, a new method for thermal analysis of PCM salts was proposed. The method was based on the estimation of heat flux at the mold–salt interface using solution to inverse heat conduction problem and characterizing the salt using a simplified energy balance method. It was advantageous over other computer-aided cooling curve analysis methods as it eliminated the use of curve fitting approach involved in baseline calculations. KNO3 and NaNO3 salts were used to validate this method. The solidification parameters like cooling rate, liquidus and solidus temperatures, solidification time and latent heat were assessed. The results of the analysis were in agreement with the data reported in the literature.
Abstract Heat flux transients at the solder/substrate interface during the solidification of Sn–3... more Abstract 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.
The failure of solder joints due to imposed stresses in an electronic assembly is governed by she... more 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.
Martempering is an industrial heat treatment process that requires a quench bath that can operate... more Martempering is an industrial heat treatment process that requires a quench bath that can operate without undergoing degradation in the temperature range of 423 K to 873 K (150 °C to 600 °C). The quench bath is expected to cool the steel part from the austenizing temperature to quench bath temperature rapidly and uniformly. Molten eutectic NaNO3-KNO3 mixture has been widely used in industry to martemper steel parts. In the present work, the effect of quench bath temperature on the cooling performance of a molten eutectic NaNO3-KNO3 mixture has been studied. An Inconel ASTM D-6200 probe was heated to 1133 K (860 °C) and subsequently quenched in the quench bath maintained at different temperatures. Spatially dependent transient heat flux at the metal–quenchant interface for each bath temperature was calculated using inverse heat conduction technique. Heat transfer occurred only in two stages, namely, nucleate boiling and convective cooling. The mean peak heat flux (q max) decreased with increase in quench bath temperature, whereas the mean surface temperature corresponding to q max and mean surface temperature at the start of convective cooling stage increased with increase in quench bath temperature. The variation in normalized cooling parameter t 85 along the length of the probe increased with increase in quench bath temperature.
Several industrial heat treatment processes, such as martempering and austempering, require a que... more Several industrial heat treatment processes, such as martempering and austempering, require a quench bath to be maintained at a temperature ranging between 150°C–600°C. Molten salts, molten alkali, and hot oils are the preferred quenchants for these processes. Molten salts and molten alkali are preferred over hot oil because they possess properties like wide operating temperature range, excellent thermal stability, and tolerance for contaminants. In the present work, the performance of a molten potassium nitrate (KNO3) quench bath was analyzed with an Inconel probe that measured 60 mm in height and 12.5 mm in diameter. The probe was heated to 850°C and subsequently quenched in a bath maintained at 450°C. Cooling curves at different locations of the probe were recorded using the K-type thermocouples inserted into the probe. Spatially dependent transient heat flux at the metal/quenchant interface was estimated using inverse heat conduction technique. The existence of two stages of quenching—boiling stage and convection stage—was confirmed by analyzing the heat flux. The heat transfer coefficient was calculated based on heat flux obtained by the inverse method. The nonuniformity in heat transfer along the length of the probe was quantified by calculating the range of surface temperatures at each instance. The hardness distribution in an AISI 4140 steel was predicted using the temperature distribution in the Inconel probe and obtained using inverse method. Uneven distribution of hardness predicted in the probe was attributed to the nonuniform cooling of the probe during quenching.
International Journal of Cast Metals Research, 2003
Heat flow between the casting and the mould during solidification of three commercially pure meta... more 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.
International Journal of Cast Metals Research, 2016
The effect of cerium melt treatment on microstructure and mechanical properties of gravity die ca... more The effect of cerium melt treatment on microstructure and mechanical properties of gravity die cast Al-8% Si alloy was studied. The addition of Ce transformed the large columnar α-Al grains into fine equiaxed grains and modified the acicular eutectic Si into fine fibrous form. The addition of Ce resulted in the formation of needle-shaped complex Ce intermetallic along the grain boundaries. Electrical conductivity measurements are used for the first time to reveal the effect of Ce addition on modification of the eutectic Si. The electrical conductivity of the alloy increased with Ce melt treatment. Scanning Electron Microscopy results suggests that the Ce particles did not heterogeneously nucleate the α-Al grains, instead the fine equiaxed grains were formed through an invariant reaction between the liquid melt and Ce phase. The ultimate tensile strength, % elongation and hardness of the alloy significantly improved due to simultaneous modification and refinement.
Journal of Materials Engineering and Performance, 2016
The present work involves the study of the effect of varying concentration of Ce addition on micr... more The present work involves the study of the effect of varying concentration of Ce addition on microstructure and mechanical properties of Al-23%Si alloys. Melt-treated alloys were solidified in copper, brass, stainless steel molds to assess the effect of cooling rate. The effect on microstructure was assessed by measuring the fineness of primary silicon and eutectic silicon particle characteristics. The Ce melt treatment transformed the coarse and irregular primary silicon into refined polyhedral silicon crystals, and the effect was more significant at higher cooling rates. Although the melt treatment had refined the eutectic silicon at lower cooling rates, it did not show any considerable effect on the eutectic silicon at higher cooling rates. The mechanical properties of the alloy increased significantly with increase in cooling rates and cerium concentration. Analysis of the results and literature reveals that the refined primary silicon was formed as a result of an invariant reaction between Ce compounds and primary silicon at higher temperatures.
The effect of varying concentrations (0 to 100 vol pct) of glycol polymer solution on wetting kin... more The effect of varying concentrations (0 to 100 vol pct) of glycol polymer solution on wetting kinetics, kinematics, and cooling performance during immersion quenching was studied by using goniometry, online video imaging, and cooling curve analysis techniques. An increase in concentration of the polymer solution resulted in improved wettability and accelerated spreading kinetics of the quench medium. The quench medium showed medium-fast-nonuniform, fast-uniform, slow-uniform, explosive/rapid, repeated, and slow-nonuniform rewetting phenomena depending on the concentration of the polymer solution. The collapse of the vapor film was by an instantaneous rupture process in the quench medium containing more water and by nucleation of bubbles caused by the selective rupture process in the quench medium enriched with polymer. The quench medium consisting of an equal amount of water and polymer showed an explosive collapse of the vapor film on the quench probe surface. The nature of the wetting front was uniform with polymer quench media except at 100 vol pct concentration of polymer quenchant. There was enhancement in the cooling performance of the quench medium, which was enhanced for a lower volume concentration of the polymer solution. However, an increase in the concentration of the polymer resulted in a decreased cooling performance. The cooling of the probe was more uniform with polymer quenchants (5 to 25 vol pct), which exhibited fast and uniform rewetting. Polymer quenchants (75 to 100 vol pct) that exhibited repeated and slow-nonuniform rewetting showed large variation in heat transfer over the quench probe surface.
Computer aided cooling curve analysis (CACCA) is an online prediction tool for the determination ... more Computer aided cooling curve analysis (CACCA) is an online prediction tool for the determination of solidification characteristics of metals or alloys. The results of CACCA can be used to accurately determine latent heat and solid fraction needed for modeling of the solidification process. Newtonian and Fourier analysis techniques adopt a data base line fitting technique to the first derivative curve for calculation of the solid fraction and latent heat of solidification. This paper describes the theoretical and experimental procedures involved Newtonian and Fourier analysis techniques with reference to an Al-22% Si alloy. The correlations between the solid fraction and temperature/time for the alloy were determined.
Simulation of heat transfer during quenching was carried out using finite difference heat transfe... more Simulation of heat transfer during quenching was carried out using finite difference heat transfer based SolidCast software. Copper, Inconel 600, Nickel, Silver and Type 304 stainless steel were chosen as quench probe material and were of cylindrical geometry with a length to diameter ratio of 5. Simulations were carried out at different combinations of heat transfer coefficient (500 to 10000 W/m2K) and quench probe diameter (0.25 to 5”). Temperature at the geometric centre of the probe was estimated and plotted against time. From the temperature – time curve the average cooling rate was determined by taking linear portion of the curve. Simulation results indicate that there is a critical diameter above which increase in cooling rate at the centre of probe is negligible for a material even with a quench medium having a very high severity of cooling. A simple quantitative model which correlates probe material, section size and cooling severity of quench media was proposed. The result...
Transactions of the Indian Institute of Metals, 2015
Solder interconnect reliability is exceedingly influenced by the solder material properties, the ... more Solder interconnect reliability is exceedingly influenced by the solder material properties, the intermetallics formed during soldering, and the environmentally imposed loads. The current study involves the study of the wetting behaviour, interfacial reactions and growth of intermetallic compounds (IMCs) in Sn–2.5Ag–0.5Cu lead free solder solidified on Cu substrate as function of reflow time. The reflow temperature was maintained at 270 °C and reflow time was varied from 10 to 10,000 s. The solder alloy showed better wettability on the substrate with the increase in reflow time. A growth in Cu6Sn5 IMC thickness was observed up to a reflow time of 500 s. IMC layer formed during a reflow time of 10 s was 3.09 μm and its thickness increased to 4.40, 8.21, 10.96 μm during 100, 300 and 500 s reflow time respectively. A decrease in the thickness of IMC was observed for samples reflowed for 1000 s. The IMC thickness increased with further increase in reflow time. The joint reliability of Sn–2.5Ag–0.5Cu solder solidified on copper substrate surfaces was assessed by performing bond shear test. The average shear strength decreased with an increase in reflow time after an optimum value.
In the present work, investigation was carried out to study the suitability of vegetable oil blen... more In the present work, investigation was carried out to study the suitability of vegetable oil blends with mineral oil and alumina based nanofluida 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 behaviuor of oils and their blends was modelled by a power law of the type: θ = kt. Wettability of nanofluids was found to poor.
Heat Treat 2019: Proceedings from the 30th Heat Treating Society Conference and Exposition
The present work presents a comprehensive comparative study on the cooling performance of hot oil... more The present work presents a comprehensive comparative study on the cooling performance of hot oil and molten KNO3- NaNO2-NaNO3 eutectic mixture quench media. The study was conducted using a cylindrical Inconel probe of 16? and 60mm length. Cooling curves at different locations in the probe were acquired using thermocouples- DAQ system. The temperature data was recorded in PC and was subsequently used to calculate spatially dependent transient heat flux at the metal quenchant interface. The heat extraction mechanism in hot oil and NaNO2 eutectic mixture was different. Quench heat transfer occurred in two stages namely boiling stage and convective cooling stage during quenching in molten NaNO2 eutectic mixture. In the case of hot oil, apart from these two stages, third stage of cooling namely vapor blanket stage was observed. A detailed study was conducted to compare magnitude and uniformity of heat extraction during each stage of quenching. Molten salt offered higher cooling rate and...
Abstract The present study is focused on the development of low Ag content 99Sn-0.3Ag-0.7Cu (SAC0... more Abstract The present study is focused on the development of low Ag content 99Sn-0.3Ag-0.7Cu (SAC0307) solder alloy with Al2O3 nanoparticles reinforcement. The effects of multiple reflow cycles and the addition of Al2O3 nanoparticles in 0.01, 0.05, 0.1, 0.3 and 0.5 percentages by weight on microstructure development and mechanical strength of the solcder joint were first investigated. The addition of ceramic nanoparticles in 0.01-0.5 wt% range resulted in 15-40% increase in the wetting area and about 10-55% increase in the microhardness of the solder. The shear strength of nanoparticles reinforced SAC0307 solder joint increased by 11-53% under multiple reflow conditions. Nano-composite solder joints containing 0.01 and 0.05 wt% Al2O3 nanoparticles showed superior shear strength and improved ductility for two reflow cycles. Hence, these nano-composites were selected and tested for their performance and joint reliability. The surface mount 2220 capacitor joint assemblies with the selected nano-composites reflowed on bare copper and Ni–P coated Cu substrates were investigated. The reliability of the solder joint was assessed by determining the joint shear strength under varying temperature environments. The nano-composite with 0.05 wt% nanoparticles addition resulted in maximum joint reliability compared to monolithic solder. The Ni–P coating on the Cu substrate significantly hindered the IMC growth at the joint interface under different thermal conditions. The joint strength improved by about 26% for samples reflowed on Ni–P surface finish compared to that on bare Cu metallization. The Weibull analysis of the joint shear strength under all thermal conditions suggest that the addition of Al2O3 nanoparticles in very small amounts to SAC0307 solder and the presence of Ni–P surface finish on Cu substrate significantly enhances the performance and reliability of solder joints. In terms of both quality and reliability, the newly developed low-silver content SAC0307+0.05Al2O3 nano-composite is an effective alternate lead-free solder that can be used in microelectronics industry in place of high-silver content Sn–Ag–Cu solders.
In the present study, wettability, interfacial intermetallic growth and shear strength of Sn–Cu e... more In the present study, wettability, interfacial intermetallic growth and shear strength of Sn–Cu eutectic solder solidified on bare as well as nickel-coated copper substrates were examined. Sn–0.7Cu solder was reflowed over the substrate for reflow times ranging from 10 to 500 s at 270 °C. Samples were cooled by quenching in water. The wetting behavior was similar on both the substrates. The corresponding time period to the end of gravity zone (Tgz) was measured from the relaxation curve obtained from wetting studies. Tgz was found to be 25 s for Sn–0.7Cu on bare and 50 s on Ni-coated copper substrates. The intermetallic compound layer thickness was fitted to a growth model to study the growth kinetics. The integrity of solder/substrate joint was assessed by performing ball as well as single-lap joint shear tests. The shear strength was found to be maximum at Tgz for all solder/substrate systems.
Cooling behaviour of steels in quench media is of great importance as this controls phase transfo... more Cooling behaviour of steels in quench media is of great importance as this controls phase transformations, heat transfer and the stress evolution. The heat extraction ability of each quenchant is different because of varying thermophysical properties and wetting behaviour. The quenchants should be selected in such a way that they provide uniform cooling of steel. In the present investigation, quenching experiments were carried out with Inconel 600, EN19, EN24, EN31 steel grades in distilled water, servo oil, carbonated distilled water and 10% PAG. The cooling curve analysis of the quenching process was carried out with temperature data recorded during quenching. This measured temperature–time data were used to estimate the heat flux by inverse modelling without considering the effect of phase transformation. The crack propensity was quantified using the quench uniformity ratio. The hardness distribution observed during quenching in carbonated distilled water was observed to be more uniform compared to other quench media.
Solar energy storage technologies have proved to be promising in terms of providing uninterrupted... more Solar energy storage technologies have proved to be promising in terms of providing uninterrupted power supply. The phase change materials (PCMs) with their higher heat storage capacity are more efficient than sensible heat storage materials. In this study, a new method for thermal analysis of PCM salts was proposed. The method was based on the estimation of heat flux at the mold–salt interface using solution to inverse heat conduction problem and characterizing the salt using a simplified energy balance method. It was advantageous over other computer-aided cooling curve analysis methods as it eliminated the use of curve fitting approach involved in baseline calculations. KNO3 and NaNO3 salts were used to validate this method. The solidification parameters like cooling rate, liquidus and solidus temperatures, solidification time and latent heat were assessed. The results of the analysis were in agreement with the data reported in the literature.
Abstract Heat flux transients at the solder/substrate interface during the solidification of Sn–3... more Abstract 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.
The failure of solder joints due to imposed stresses in an electronic assembly is governed by she... more 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.
Martempering is an industrial heat treatment process that requires a quench bath that can operate... more Martempering is an industrial heat treatment process that requires a quench bath that can operate without undergoing degradation in the temperature range of 423 K to 873 K (150 °C to 600 °C). The quench bath is expected to cool the steel part from the austenizing temperature to quench bath temperature rapidly and uniformly. Molten eutectic NaNO3-KNO3 mixture has been widely used in industry to martemper steel parts. In the present work, the effect of quench bath temperature on the cooling performance of a molten eutectic NaNO3-KNO3 mixture has been studied. An Inconel ASTM D-6200 probe was heated to 1133 K (860 °C) and subsequently quenched in the quench bath maintained at different temperatures. Spatially dependent transient heat flux at the metal–quenchant interface for each bath temperature was calculated using inverse heat conduction technique. Heat transfer occurred only in two stages, namely, nucleate boiling and convective cooling. The mean peak heat flux (q max) decreased with increase in quench bath temperature, whereas the mean surface temperature corresponding to q max and mean surface temperature at the start of convective cooling stage increased with increase in quench bath temperature. The variation in normalized cooling parameter t 85 along the length of the probe increased with increase in quench bath temperature.
Several industrial heat treatment processes, such as martempering and austempering, require a que... more Several industrial heat treatment processes, such as martempering and austempering, require a quench bath to be maintained at a temperature ranging between 150°C–600°C. Molten salts, molten alkali, and hot oils are the preferred quenchants for these processes. Molten salts and molten alkali are preferred over hot oil because they possess properties like wide operating temperature range, excellent thermal stability, and tolerance for contaminants. In the present work, the performance of a molten potassium nitrate (KNO3) quench bath was analyzed with an Inconel probe that measured 60 mm in height and 12.5 mm in diameter. The probe was heated to 850°C and subsequently quenched in a bath maintained at 450°C. Cooling curves at different locations of the probe were recorded using the K-type thermocouples inserted into the probe. Spatially dependent transient heat flux at the metal/quenchant interface was estimated using inverse heat conduction technique. The existence of two stages of quenching—boiling stage and convection stage—was confirmed by analyzing the heat flux. The heat transfer coefficient was calculated based on heat flux obtained by the inverse method. The nonuniformity in heat transfer along the length of the probe was quantified by calculating the range of surface temperatures at each instance. The hardness distribution in an AISI 4140 steel was predicted using the temperature distribution in the Inconel probe and obtained using inverse method. Uneven distribution of hardness predicted in the probe was attributed to the nonuniform cooling of the probe during quenching.
International Journal of Cast Metals Research, 2003
Heat flow between the casting and the mould during solidification of three commercially pure meta... more 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.
International Journal of Cast Metals Research, 2016
The effect of cerium melt treatment on microstructure and mechanical properties of gravity die ca... more The effect of cerium melt treatment on microstructure and mechanical properties of gravity die cast Al-8% Si alloy was studied. The addition of Ce transformed the large columnar α-Al grains into fine equiaxed grains and modified the acicular eutectic Si into fine fibrous form. The addition of Ce resulted in the formation of needle-shaped complex Ce intermetallic along the grain boundaries. Electrical conductivity measurements are used for the first time to reveal the effect of Ce addition on modification of the eutectic Si. The electrical conductivity of the alloy increased with Ce melt treatment. Scanning Electron Microscopy results suggests that the Ce particles did not heterogeneously nucleate the α-Al grains, instead the fine equiaxed grains were formed through an invariant reaction between the liquid melt and Ce phase. The ultimate tensile strength, % elongation and hardness of the alloy significantly improved due to simultaneous modification and refinement.
Journal of Materials Engineering and Performance, 2016
The present work involves the study of the effect of varying concentration of Ce addition on micr... more The present work involves the study of the effect of varying concentration of Ce addition on microstructure and mechanical properties of Al-23%Si alloys. Melt-treated alloys were solidified in copper, brass, stainless steel molds to assess the effect of cooling rate. The effect on microstructure was assessed by measuring the fineness of primary silicon and eutectic silicon particle characteristics. The Ce melt treatment transformed the coarse and irregular primary silicon into refined polyhedral silicon crystals, and the effect was more significant at higher cooling rates. Although the melt treatment had refined the eutectic silicon at lower cooling rates, it did not show any considerable effect on the eutectic silicon at higher cooling rates. The mechanical properties of the alloy increased significantly with increase in cooling rates and cerium concentration. Analysis of the results and literature reveals that the refined primary silicon was formed as a result of an invariant reaction between Ce compounds and primary silicon at higher temperatures.
The effect of varying concentrations (0 to 100 vol pct) of glycol polymer solution on wetting kin... more The effect of varying concentrations (0 to 100 vol pct) of glycol polymer solution on wetting kinetics, kinematics, and cooling performance during immersion quenching was studied by using goniometry, online video imaging, and cooling curve analysis techniques. An increase in concentration of the polymer solution resulted in improved wettability and accelerated spreading kinetics of the quench medium. The quench medium showed medium-fast-nonuniform, fast-uniform, slow-uniform, explosive/rapid, repeated, and slow-nonuniform rewetting phenomena depending on the concentration of the polymer solution. The collapse of the vapor film was by an instantaneous rupture process in the quench medium containing more water and by nucleation of bubbles caused by the selective rupture process in the quench medium enriched with polymer. The quench medium consisting of an equal amount of water and polymer showed an explosive collapse of the vapor film on the quench probe surface. The nature of the wetting front was uniform with polymer quench media except at 100 vol pct concentration of polymer quenchant. There was enhancement in the cooling performance of the quench medium, which was enhanced for a lower volume concentration of the polymer solution. However, an increase in the concentration of the polymer resulted in a decreased cooling performance. The cooling of the probe was more uniform with polymer quenchants (5 to 25 vol pct), which exhibited fast and uniform rewetting. Polymer quenchants (75 to 100 vol pct) that exhibited repeated and slow-nonuniform rewetting showed large variation in heat transfer over the quench probe surface.
Computer aided cooling curve analysis (CACCA) is an online prediction tool for the determination ... more Computer aided cooling curve analysis (CACCA) is an online prediction tool for the determination of solidification characteristics of metals or alloys. The results of CACCA can be used to accurately determine latent heat and solid fraction needed for modeling of the solidification process. Newtonian and Fourier analysis techniques adopt a data base line fitting technique to the first derivative curve for calculation of the solid fraction and latent heat of solidification. This paper describes the theoretical and experimental procedures involved Newtonian and Fourier analysis techniques with reference to an Al-22% Si alloy. The correlations between the solid fraction and temperature/time for the alloy were determined.
Simulation of heat transfer during quenching was carried out using finite difference heat transfe... more Simulation of heat transfer during quenching was carried out using finite difference heat transfer based SolidCast software. Copper, Inconel 600, Nickel, Silver and Type 304 stainless steel were chosen as quench probe material and were of cylindrical geometry with a length to diameter ratio of 5. Simulations were carried out at different combinations of heat transfer coefficient (500 to 10000 W/m2K) and quench probe diameter (0.25 to 5”). Temperature at the geometric centre of the probe was estimated and plotted against time. From the temperature – time curve the average cooling rate was determined by taking linear portion of the curve. Simulation results indicate that there is a critical diameter above which increase in cooling rate at the centre of probe is negligible for a material even with a quench medium having a very high severity of cooling. A simple quantitative model which correlates probe material, section size and cooling severity of quench media was proposed. The result...
Transactions of the Indian Institute of Metals, 2015
Solder interconnect reliability is exceedingly influenced by the solder material properties, the ... more Solder interconnect reliability is exceedingly influenced by the solder material properties, the intermetallics formed during soldering, and the environmentally imposed loads. The current study involves the study of the wetting behaviour, interfacial reactions and growth of intermetallic compounds (IMCs) in Sn–2.5Ag–0.5Cu lead free solder solidified on Cu substrate as function of reflow time. The reflow temperature was maintained at 270 °C and reflow time was varied from 10 to 10,000 s. The solder alloy showed better wettability on the substrate with the increase in reflow time. A growth in Cu6Sn5 IMC thickness was observed up to a reflow time of 500 s. IMC layer formed during a reflow time of 10 s was 3.09 μm and its thickness increased to 4.40, 8.21, 10.96 μm during 100, 300 and 500 s reflow time respectively. A decrease in the thickness of IMC was observed for samples reflowed for 1000 s. The IMC thickness increased with further increase in reflow time. The joint reliability of Sn–2.5Ag–0.5Cu solder solidified on copper substrate surfaces was assessed by performing bond shear test. The average shear strength decreased with an increase in reflow time after an optimum value.
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Papers by NARAYAN PRABHU