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Author: search.filters.author.Vijayan, V.

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    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.
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    Failures Investigation of Marine Propellers in Corrosive Environments
    (Springer Nature, 2021) Mirashi, V.U.; Johnson, S.; Hegde, S.; Vijayan, V.; Cadambi, S.
    Marine corrosion failure of fishing boat propellers made of cast Nickel Aluminium Bronze were investigated. Specimens extracted from the corroded propellers were characterized by optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy. The alloy comprises several Fe3Al (κ1, κ2, κ4), NiAl (κ3) type intermetallic precipitates and β’ martensite embedded in Cu-rich α-matrix. Transverse sections of the corroded region showed two distinct zones; a non-uniform top oxide layer and a partially corroded zone with selective corrosion of the β’ martensite which run parallel to the κ3 precipitates. From the microstructural analysis it is adjudged that the aggressive local corrosion of the matrix is preceded by cracking of the oxide by erosion, cavitation, etc., A slow growth of the oxide layer follows that reduces the corrosion rate. However, the corrosion cycle repeats on erosion or cracking of the oxide layer when the propeller is used in marine waters. Coupon specimens immersed in actual marine conditions is presented that supports the above theory. © 2021, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.
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    The effect of strontium modification on casting/chill interfacial heat flux and casting surface profile during solidification of Al-7Si alloy
    (Institution of Engineering and Technology jbristow@theiet.org, 2013) Vijayan, V.; Prabhu, K.N.
    The effect of Sr modification of Al-7%Si alloy on casting/chill interfacial heat flux transients was investigated. The alloy was solidified against polished surfaces of copper, brass and cast iron chills. The heat flux across the casting/chill interface was estimated using inverse modeling technique. On modification melt treatment, the peak heat flux increased by about 70%, 24% and 22% for copper, brass and cast iron chills respectively. The effect of Sr modification on casting surface texture was analyzed using a surface profilometer. The surface profile of the casting and the chill surfaces clearly indicated the formation of anair gap at the periphery of the casting. The arithmetic average value of the profile departure from the mean line, within a sampling length(Ra) and arithmetical mean of the absolute departures of the waviness profile from the centre line within a sampling length(W a) were reduced by 50% on modification. The enhancement in heat transfer achieved due to modification was attributed to the decrease in gap width formed at the interface. The width of the gap formed for the unmodified and modified casting surfaces at the periphery were found to be about 35μm and 19μm respectively. The gap width was used to determine the variation of heat transfer coefficient (HTC) acrossthe chill surface after the formation of stable solid shell.It was found that the HTC decreased along the radial direction.
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    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.
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    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.
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    Effect of cerium addition on casting/chill interfacial heat flux and casting surface profile during solidification of Al-14%Si alloy
    (Institute of Physics Publishing michael.roberts@iop.org, 2016) Vijayan, V.; Prabhu, K.
    In the present investigation, Al-14 wt. % Si alloy was solidified against copper, brass and cast iron chills, to study the effect of Ce melt treatment on casting/chill interfacial heat flux transients and casting surface profile. The heat flux across the casting/chill interface was estimated using inverse modelling technique. On addition of 1.5% Ce, the peak heat flux increased by about 38%, 42% and 43% for copper, brass and cast iron chills respectively. The effect of Ce addition on casting surface texture was analyzed using a surface profilometer. The surface profile of the casting and the chill surfaces clearly indicated the formation of an air gap at the periphery of the casting. The arithmetic average value of the profile departure from the mean line (Ra) and arithmetical mean of the absolute departures of the waviness profile from the centre line (Wa) were found to decrease on Ce addition. The interfacial gap width formed for the unmodified and Ce treated casting surfaces at the periphery were found to be about 35μm and 13μm respectively. The enhancement in heat transfer on addition of Ce addition was attributed to the lowering of the surface tension of the liquid melt. The gap width at the interface was used to determine the variation of heat transfer coefficient (HTC) across the chill surface after the formation of stable solid shell. It was found that the HTC decreased along the radial direction for copper and brass chills and increased along radial direction for cast iron chills.
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    Effect of Ce melt treatment on solidification path of ZA8 alloy
    (Institute of Physics Publishing michael.roberts@iop.org, 2016) Sudheer, R.; Vijayan, V.; Prabhu, K.
    The solidification path of ZA8 alloy with Ce addition was characterized using Newtonian technique of thermal analysis. The solidification events were determined using cooling curve and its first derivative curve. The microstructure and chemical composition of various phases in the alloy were studied using EDS, SEM and XRD techniques. It was found that the addition of Ce did not cause formation of new phases. However, it hinders the nucleation of stable β dendrites in the alloy. The presence of Ce promotes the eutectoid phase transformation and increases the hardness of the alloy. Latent heat of solidification and heat of eutectoid transformation were found to increase on Ce addition. The upward solidification of the alloy against Cu chill was analysed. Chilling had significant influence on solidification parameters, and caused refinement of the microstructure. The addition of Ce to the melt had no effect during chill casting of the alloy.
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    Effect of Ni and Sr additions on the microstructure, mechanical properties, and coefficient of thermal expansion of Al-23%Si alloy
    (Elsevier Ltd, 2021) Vijayan, V.; Ravi, M.; Prabhu, K.N.
    In this paper, the combined and individual effect of strontium (Sr) and nickel (Ni) additions on the microstructure and mechanical properties of hypereutectic Al-23Si alloy was studied using an optical microscopy, universal tensile testing machine and Brinell hardness tester. The wear properties and coefficient of thermal expansion of the melt treated samples were determined using pin on disc wear testing machine and linear expansion measurement unit respectively. The results indicate that the Ni additions significantly enhanced the mechanical properties of the alloy, whereas, presence of Sr was detrimental. It was observed that the improvement in mechanical properties due to Ni was primarily due to refinement and transformation of the star shaped primary silicon into polyhedral crystals. However, the addition of Sr, both as separate and when combined with Ni, transformed the primary silicon into a faceted crystal and hence decreased the mechanical property. Among all, the Ni melt treated alloy samples showed lowest wear rate and coefficient of thermal expansion. © 2021 Elsevier Ltd. All rights reserved.
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    Determining the solidification characteristics of Manganese bronze (MAB) alloy using computer-aided cooling curve analysis
    (Elsevier Ltd, 2022) Pranesh; Mohammed Anas, S.; Johnson, S.; Jose, R.; Sachin, B.; Cadambi, S.; Vijayan, V.; Karinka, S.
    Computer-aided cooling curve analysis (CACCA), known for its reliability and simplicity was used to study the material properties of manganese bronze (MAB) alloy. MAB alloy, due to its high strength and corrosion resistance, is a staple material for marine applications. Since the alloy is difficult to machine, non-heat treatable, and complex to fabricate, casting is the only cost-effective process of producing products of the material. As the literature is scant on the MAB's high-temperature properties, this study is aimed at determining the thermo-physical properties of the alloy required for casting simulation by carrying out Newtonian and Fourier analysis of the recorded temperature of the solidifying alloy from liquidus state. © 2022 Elsevier Ltd. All rights reserved.
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    Review of microstructure evolution in hypereutectic Al-Si alloys and its effect on wear properties
    (2014) Vijayan, V.; Prabhu, K.
    Al-Si alloys with silicon content more than 13 % are termed as hypereutectic alloys. In recent years, these alloys have drawn the attention of researchers due to their ability to replace cast iron parts in the transportation industry. The properties of the hypereutectic alloy are greatly dependent on the morphology, size and distribution of primary silicon crystals in the alloy. Mechanical properties of the hypereutectic Al-Si alloy can be improved by the simultaneous refinement and modification of the primary and eutectic silicon and by controlling the solidification parameters. In this paper, the effect of solidification rate and melt treatment on the evolution of microstructure in hypereutectic Al-Si alloys are reviewed. Different types of primary silicon morphology and the conditions for its nucleation and growth are explained. The paper discusses the effect of refinement/modification treatments on the microstructure and properties of the hypereutectic Al-Si alloy. The importance and effect of processing variables and phosphorus refinement on the silicon morphology and wear properties of the alloy is highlighted. © 2013 Indian Institute of Metals.