Faculty Publications

Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736

Publications by NITK Faculty

Browse

Author: search.filters.author.Prabhu, K.Has files: No

Search Results

Now showing 1 - 10 of 60
  • No Thumbnail Available
    Item
    The Effect of Cooling Rate and Cerium Melt Treatment on Thermal Analysis Parameters and Microstructure of Hypoeutectic Al-Si Alloy
    (Wiley Blackwell, 2015) Vijayan, V.; Prabhu, K.
    In the present investigation, pure cerium ingots were added to Al- 8% Si alloy melt to study its effect on the microstructure and cooling curve parameters. The melt treated alloy was solidified against sand base, stainless steel, brass, and copper chills to study the effect of chilling. Ce treated alloys solidified against sand base resulted in refinement of the eutectic silicon along with the formation of Al-Si-Ce ternary intermetallic compound. Addition of Ce to alloys solidified against chills resulted in the complete modification of eutectic silicon. Thermal analysis results revealed that the nucleation temperatures of eutectic silicon decreased on addition of cerium to the chilled alloys due to the synergistic effect of chilling and cerium addition. The degree of modification achieved was higher due to the decrease in the formation of Ce intermetallic s at higher cooling rates. © 2015 The Minerals, Metals & Materials Society. All rights reserved.
  • No Thumbnail Available
    Item
    Polymer Quenchants for Industrial Heat Treatment
    (CRC Press, 2016) Prabhu, K.; Nayak, V.; Rao, P.
    Flux During Quenching 732 25.12 Application of Polymeric Quenchants in Heat Treatment of Steels 734 25.13 Application of Polymeric Quenchants in Heat Treatment of Aluminum Alloys 736 25.14 Summary 738 References 739 during the quench process. Generally, a liquid quench medium is commonly used to facilitate/control the heat transfer during quenching. The most commonly used quenchants in industries worldwide is water followed by oils. On immersion quenching in these liquids, the metal experiences three typical stages of quenching: vapor stage, nucleate boiling stage, and the convective cooling stage. However, the severity of cooling and the duration of the stages in both classes are very much different. Water, because of its severe nature of cooling, provides ample, or exceeds, mechanical properties over that which is required. Moreover, in many circumstances, such as cooling of complex objects or high-alloyed steels, it causes undue distortion, residual stresses, and, in the most severe case, crack formation. Oils, by their very viscous nature, deliver lower cooling performance and reduces is the propensity towards distortion and cracking. The low quench severity of oils results in reduced properties. These limitations compelled the quenchant suppliers to develop polymer quench media that offer the benefit of both water and oils. © 2017 by Taylor and Francis Group, LLC.
  • No Thumbnail Available
    Item
    The effect of cooling rate and cerium melt treatment on thermal analysis parameters and microstructure of hypoeutectic Al-Si alloy
    (Minerals, Metals and Materials Society 184 Thorn Hill Road Warrendale PA 15086, 2015) Vijayan, V.; Prabhu, K.
    In the present investigation, pure cerium ingots were added to Al-8% Si alloy melt to study its effect on the microstructure and cooling curve parameters. The melt treated alloy was solidified against sand base, stainless steel, brass, and copper chills to study the effect of chilling. Ce treated alloys solidified against sand base resulted in refinement of the eutectic silicon along with the formation of Al-Si-Ce ternary intermetallic compound. Addition of Ce to alloys solidified against chills resulted in the complete modification of eutectic silicon. Thermal analysis results revealed that the nucleation temperatures of eutectic silicon decreased on addition of cerium to the chilled alloys due to the synergistic effect of chilling and cerium addition. The degree of modification achieved was higher due to the decrease in the formation of Ce intermetallics at higher cooling rates.
  • No Thumbnail Available
    Item
    Assessment of wetting kinematics and cooling performance of select vegetable oils and mineral-vegetable oil blend quench media
    (Trans Tech Publications Ltd ttp@transtec.ch, 2015) Pranesh Rao, K.M.; Prabhu, K.
    Quench hardening is a process where an alloy is heated to solutionizing temperature and held for a definite period, and then rapidly cooled in a quenching medium. Selection of quenchant that can yield desired properties is essential as it governs heat extraction process during quenching. In the present work, the cooling performance of vegetable oil and mineral-vegetable oil blend quench media was assessed. The vegetable oils used in this work were olive oil, canola oil and rice bran oil. The mineral-vegetable oil blends were prepared by blending 10 and 20 vol. % of rice bran and canola oil in mineral oil. Inconel probe of 12.5mm diameter and 60mm height, instrumented with thermocouples were used to characterize quenchants. The probe was heated to 850°C and quenched in the oil medium. The cooling curves at different locations in the probe were used to study wetting kinematics. Inverse modelling technique was used to estimate spatially dependent metal-quenchant interfacial heat flux. It was found that the vegetable oils exhibited very short vapour blanket stage compared to mineral oil and blends. Faster wetting kinematics obtained with blends resulted in uniform heat transfer compared to that of mineral oil. The temperature distribution in the probe quenched in vegetable oils and blends was more uniform compared to that in mineral oil. It is expected that the parts quenched in vegetable oils and blends would lead to better hardness distribution compared to mineral oils. © (2015) Trans Tech Publications, Switzerland.
  • No Thumbnail Available
    Item
    Wetting kinetics and joint strength of Sn-0.3Ag-0.7Cu lead-free solder alloy on copper substrate as a function of reflow time
    (Trans Tech Publications Ltd ttp@transtec.ch, 2015) Sona, M.; Prabhu, K.
    Solder plays a vital role in the interconnection of electronic devices in electronic assemblies. As an interconnection material, the solder joint executes electrical, mechanical and thermal functions. The use of lead bearing solders in electronic products is banned due to the toxicity and environmental risks coupled with lead. In the present study, wetting kinetics, interfacial reactions and the formation of intermetallic compounds (IMCs) during solidification of Sn-0.3Ag- 0.7Cu solder alloy on Cu substrate and the corresponding joint strength were studied as a function of reflow time. Experiments were carried out at various reflow times of 10, 100, 300 and 500s. The reflow temperature was maintained at 270°C. The solder alloy showed enhanced wettability on the substrate at longer reflow times. The thickness of IMC layer formed during a reflow time of 10s was 1.67μm and the thickness increased to 2.20μm, 2.85μm, 2.91μm during 100s, 300s and 500s of reflow time respectively. The joint shear test was performed to assess the integrity of Sn-0.3Ag- 0.7Cu solder solidified on Cu substrates using Nordson DAGE 4000 Plus bond tester. The joint strength increased with the increase in reflow time up to 300s and the maximum joint strength was observed for samples reflowed for 300s. Although the samples reflowed for 500s samples showed good wettability, they exhibited lowest joint strength. © (2015) Trans Tech Publications, Switzerland.
  • No Thumbnail Available
    Item
    Centrifugal casting and characterisation of primary silicon and Mg2Si dispersed aluminium functionally graded materials
    (Trans Tech Publications Ltd ttp@transtec.ch, 2015) Midhun Krishnan, P.; Sanil, S.; Jayakumar, E.; Rajan, T.P.D.; Prabhu, K.
    Aluminium based FGM rings, reinforced by in-situ primary Si and primary Si/ Mg2Si hybrid reinforcement were successfully fabricated by centrifugal casting and micro structural, chemical, hardness and corrosion characteristics were evaluated. It was observed that in Al-20Si ring the primary Si particles were present mostly in inner region and few in outer region where as in Al-20Si-3Mg ring both the primary silicon and Mg2Si were completely found in the inner region only resulting in a graded FGM structure. The hardness values were measured along radial direction of samples and variations corresponding to micro structural variation were analysed. Optical Emission spectroscopic studies have revealed the remarkable compositional changes along radial direction. Corrosion characteristics were also evaluated both in particle rich and depleted regions. © (2015) Trans Tech Publications, Switzerland.
  • No Thumbnail Available
    Item
    Assessment of latent heat and solid fraction of Al-22Si alloy using Newtonian and Fourier analysis techniques
    (Trans Tech Publications Ltd ttp@transtec.ch, 2015) Vijayan, V.; Prabhu, K.
    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. © (2015) Trans Tech Publications, Switzerland.
  • No Thumbnail Available
    Item
    Wettability and bond shear strength of Sn-9Zn lead-free solder alloy reflowed on copper substrate
    (Trans Tech Publications Ltd ttp@transtec.ch, 2015) Tikale, S.; Sona, M.; Prabhu, K.
    Lead-free solders are environment friendly and are in great demand for microelectronic applications. In the present study, Sn-9Zn lead free solder alloy was solidified on Cu substrate for different reflow times varying from 10 to 1000s. The influence of reflow time on wetting, bond shear strength and formation of intermetallic compounds (IMCs) was studied using dynamic contact angle analyzer, bond tester and scanning electron microscopy (SEM), respectively. The results indicate that, the wettability of the solder alloy increased with increase in reflow time. Microstructure study revealed the presence of Cu5Zn8 and CuZn5 IMCs at the interface. The thickness of an IMC increased with increase in the reflow time. A mean thickness of Cu5Zn8 IMC layer of about 11μm was obtained for a reflow time of 1000s. The thickness of CuZn5 layer increased up to a reflow time of 100s and decreased thereafter. The bond shear strength increased up to 100s and decreased with increase in reflow time. The decrease in shear strength at higher reflow time is mainly due to the formation of thick Cu5Zn8 IMC layer and diffusion of Sn from bulk solder towards the substrate. The thick IMC layer exhibited micro-cracks leading to the brittle failure of bond under the influence of shear stress. © (2015) Trans Tech Publications, Switzerland.
  • No Thumbnail Available
    Item
    Characterization of metal-PCMs for thermal energy storage applications
    (Trans Tech Publications Ltd ttp@transtec.ch, 2015) Sudheer, R.; Prabhu, K.
    In recent years phase change materials have emerged to be ideal energy storage materials for their higher energy density over sensible heat storing materials. Use of phase change materials (PCM) have been successfully implemented at lower temperature applications with various organic compounds. On the other hand, high temperature applications have been solely dominated by various salts, their eutectics and mixtures as phase change materials. This work discusses the suitability of metals and alloys for thermal energy storage applications as the phase change material. Metals offer superior thermal conductivities with considerable energy density compared to salts. Here, two alloys namely, Sn-0.3Ag-0.7Cu (SAC) solidifying over 212-224°C and ZA8 (Zn-8%Al) solidifying over 378-405°C have been studied. Thermal analysis of PCMs using Computer Aided Cooling Curve Analysis (CA-CCA) and DSC technique were performed to predict the solidification path. In addition to this, Newtonian technique was employed to estimate the latent heat of fusion for these phase change materials. Cooling rate curves and Fraction Solid curves offered a better insight into their ability to receive and discharge heat over the concerned temperature range. © (2015) Trans Tech Publications, Switzerland.
  • No Thumbnail Available
    Item
    Heat transfer during immersion quenching in MWCNT nanofluids
    (Trans Tech Publications Ltd ttp@transtec.ch, 2015) Nayak, U.; Prabhu, K.
    Quench heat treatment consists of rapid cooling of steel alloys after austenetization by subjecting them to cooling in a suitable cooling medium. At the heart of quench treatment is the transient heat transfer that occurs between the metal surface and the quenchant at their interface. This governs the quality of the component as it influences phase transformation, residual quench stresses and mechanical properties developed. In the present research work, spatially dependent transient heat flux in the axial direction was estimated using cooling curve analyses coupled with inverse heat conduction technique. A standard Inconel 600 probe instrumented with multiple thermocouples and heated to 865°C was quenched in distilled water (DW) and DW based multi walled carbon nanotubes (MWCNT) quench media. For evaluating the cooling performance, nanoquenchants with concentrations of 0.01, 0.1 and 1.0g/lt. were prepared. The cooling rate curve calculated from the measured temperature at the geometric center of the probe and the estimation of spatially dependent heat fluxes showed that the heat extraction during quenching with MWCNT nanoquenchant (0.1g/lt.) was higher than the other quenchants. The measured values of thermal conductivity and viscosities of quenchants did not show any significant variation. © (2015) Trans Tech Publications, Switzerland.