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Krishnamohan S.,Egs Pillay Engineering College | Ramanathan S.,Annamalai University | Ramakrishnan V.,Thermal Systems Group
Journal of Computational and Theoretical Nanoscience | Year: 2017

The elevated strength, low weight ratio and excellent corrosion resistance intrinsic to titanium and its alloys has led to a wide range of successful applications which ensures high levels of unswerving performance in aerospace. The performance of the Thermal Control System extremely depends on the thermal behavior of the materials used in its elements. The measurements of the thermal properties of materials are necessary for better understanding of the thermal design. Differential scanning calorimetry (DSC) is the most extensively used thermal method for finding wealth of information about a material. The heat capacity (Cp) of a material was established quantitatively using DSC. The measurement was made by heating a very small quantity of the Ti6Al4V alloy and Ti6Al4V/Nano SiCp composites. Mechanical alloying (MA) and Powder metallurgy (P/M) techniques were used to fabricate the Ti6Al4V alloy and Ti6Al4V/ nano SiCp composites. The heat flow reaction was recorded as a function of definite sample temperature range from -100 °C to 375 °C. The measurements of the heat capacity of each sample in three runs were recorded by DSC. The heat capacity (Cp) of specimens is reported in this study. © 2017 American Scientific Publishers.

Parida B.,Thermal Systems Group | Rani R.U.,Thermal Systems Group | Sharma A.K.,Thermal Systems Group
Surface Engineering | Year: 2010

A novel galvanic conversion coating was studied on magnesium alloy AZ31B in an electrolyte system consisting of ammonium molybdate and magnesium chloride. The conditions of the conversion coating process and the characteristic of the coatings are studied in detail. The coatings were characterised by energy dispersive X-ray, infrared spectral and scanning electron microscopy studies. The thermoanalytical investigations have been carried out using thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC). The space worthiness of the coating was evaluated by environmental tests, namely, humidity, thermal cycling, thermovacuum performance and thermal stability tests. Optical properties (solar absorptance and infrared emittance) were measured before and after each environmental test to ascertain its stability. The coating provides higher solar absorptance and infrared emittance in the order of ∼0·80. The developed procedure is simple, ecofriendly and economically viable. © 2010 Institute of Materials, Minerals and Mining.

Sharma A.K.,Thermal Systems Group | Sridhara N.,Thermal Systems Group
Advances in Space Research | Year: 2012

A spacecraft with a passive thermal control system utilizes various thermal control materials to maintain temperatures within safe operating limits Materials used for spacecraft applications are exposed to harsh space environments such as ultraviolet (UV) and particle (electron, proton) irradiation and atomic oxygen (AO), undergo physical damage and thermal degradation, which must be considered for spacecraft thermal design optimization and cost effectiveness This paper describes the effect of synergistic radiation on some of the important thermal control materials to verify the assumptions of beginning-of-life (BOL) and end-of-life (EOL) properties Studies on the degradation in the optical properties (solar absorptance and infrared emittance) of some important thermal control materials exposed to simulated radiative geostationary space environment are discussed The current studies are purely related to the influence of radiation on the degradation of the materials; other environmental aspects (e.g.; thermal cycling) are not discussed The thermal control materials investigated herein include different kind of second-surface mirrors, white anodizing, white paints, black paints, multilayer insulation materials, varnish coated aluminized polyimide, germanium coated polyimide, polyether ether ketone (PEEK) and poly tetra fluoro ethylene (PTFE) For this purpose, a test in the constant vacuum was performed reproducing a three year radiative space environment exposure, including ultraviolet and charged particle effects on North/South panels of a geostationary three-axis stabilized spacecraft Reflectance spectra were measured in situ in the solar range (250-2500 nm) and the corresponding solar absorptance values were calculated The test methodology and the degradations of the materials are discussed The most important degradations among the low solar absorptance materials were found in the white paints whereas the rigid optical solar reflectors remained quite stable Among the high solar absorptance elements, as such the change in the solar absorptance was very low, in particular the germanium coated polyimide was found highly stable © 2012 COSPAR Published by Elsevier Ltd All rights reserved.

Pillai A.M.,Thermal Systems Group | Rajendra A.,Thermal Systems Group | Sharma A.K.,Thermal Systems Group
Transactions of the Institute of Metal Finishing | Year: 2012

Electrodeposition of nanocrystalline nickel on aluminium alloy AA 6061 substrate was carried out using cathodic square wave pulse with an on-time of 0?1 ms and an off-time of 0?9 ms from a modified Watt's bath containing saccharin as an additive. The influences of concentration of saccharin, pH of the plating bath and average current density on the surface morphology, crystal orientation, average grain size and lattice strain were investigated. The study confirms that increase in concentration of saccharin in the plating bath as well as increase in the average current density results in a decrease in the average grain size of the deposit. pH appears to have no significant effect on the grain size of the deposit. The crystal orientation progressively changes from a strong (200) fibre structure to a (111) (200) double fibre structure as the concentration of saccharin is increased in the plating bath. It was also observed that as the grain size decreases the lattice strain of the coating increases. The space worthiness of the coating has been evaluated by humidity, thermal cycling, thermovacuum performance tests and measurement of optical properties. The coatings were characterised by scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy analysis, microhardness evaluation, adhesion, thermal stability and corrosion resistance tests. © 2012 Institute of Metal Finishing.

Dey A.,Thermal Systems Group | Mukhopadhyay A.K.,Indian Central Glass and Ceramic Research Institute
Ceramics International | Year: 2014

The evaluation of residual stress in bioactive hydroxyapatite (HAP) ceramic coating by nanoindentation technique has been attempted successfully for the very first time ever in the present work. The HAP coatings were deposited on surgical grade 316 L austenitic stainless steel and Ti-6Al-4V substrates by microplasma spraying (MIPS) process. The coatings had Ca/P ratio of 1.67 and were ∼80-90% crystalline. The results showed a residual compressive stress of ∼22 MPa for the MIPS-HAP coatings on the SS316L substrates. For the coatings deposited on the Ti-6Al-4V substrates, however, a residual tensile stress of ∼11 MPa was estimated. These data matched well with those obtained by XRD based technique. Thus, favorable data comparison provides further support to the efficacy of the nanoindentation based technique utilized in the present work for residual stress estimations. © 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Pillai A.M.,Thermal Systems Group | Rajendra A.,Thermal Systems Group | Sharma A.K.,Thermal Systems Group
Transactions of the Institute of Metal Finishing | Year: 2012

Pulse electrodeposition of nanocrystalline nickel has been carried out on AA 6061 substrate from a modified Watt's bath using saccharin as a grain refining additive. By varying the concentration of saccharin and other operating parameters, nanocrystalline nickel electrodeposits of varying average grain sizes (from 115 down to 17 nm) have been obtained. Nanoindentation was employed for studying the effect of average grain size on the mechanical and tribological properties of the electrodeposits, with emphasis on hardness, elastic modulus, wear resistance and coefficient of friction. The study confirms that the hardness of nanocrystalline nickel electrodeposits increases as the average grain size decreases and a value as high as 7·2 GPa is obtained for a coating having an average grain size of 17 nm. No inverse Hall-Petch relationship is observed for the entire range of grain sizes studied. The elastic modulus of the electrodeposits remained almost constant (between 150 and 160 GPa), irrespective of the average grain size and a coefficient of friction value of 0·25 has been obtained for a deposit having an average grain size of 17 nm. © 2012 Institute of Metal Finishing.

Pillai A.M.,Thermal Systems Group | Rajendra A.,Thermal Systems Group | Sharma A.K.,Thermal Systems Group
Journal of Coatings Technology Research | Year: 2012

Ni-P deposits with a phosphorous content of up to 20% (wt) were obtained on AA6061 substrates by direct current electrodeposition technique from a solution containing nickel sulfate, nickel chloride, phosphorous acid, phosphoric acid, and a wetting agent (sodium lauryl sulfate). The effect of various plating parameters like current density, concentration of phosphorous acid, concentration of phosphoric acid and plating temperature on the P content of the coating as well as the rate of deposition was investigated systematically. It has been observed that the influence of current density on the P content of the deposit is largely dependent on the concentration of phosphorous acid in the plating bath. Composition, surface morphology, microstructure, and mechanical properties of the Ni-P deposits were studied using SEM, EDAX, XRD, and nanoindentation techniques. Ni-P electrodeposits with low P content in the range of 4-7 wt% of P exhibited superior microhardness of 7.74-8.57 GPa. With increasing P content in the deposit, the structure undergoes transition from crystalline to nanocrystalline and becomes amorphous above 9.14 wt% of P. Ni-P alloys with some selected compositions were subjected to heat treatment at 400°C for 1 h in a hot air oven and the resulting variation in mechanical properties was studied using nanoindentation technique. © ACA and OCCA 2012.

Dey A.,Thermal Systems Group | Rani R.U.,Thermal Systems Group | Thota H.K.,Thermal Systems Group | Sharma A.K.,Thermal Systems Group | And 2 more authors.
Ceramics International | Year: 2013

Microstructural, corrosion and nanomechanical behaviour of micro arc oxidised (MAO) coating grown on magnesium AZ31B alloy was evaluated. Microstructural characterization of the coating was carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) followed by image analysis and energy dispersive spectroscopy (EDX). Linear polarization technique was used to evaluate the corrosion behaviour of the MAO coating. Further, nanoindentation was employed to evaluate nanohardness and Young's modulus of the MAO coating. The characteristic values of both the nanohardness and the Young's modulus were calculated through the application of the Weibull statistics. © 2012 Elsevier Ltd and Techna Group S.r.l.

Karthikeyan B.,Annamalai University | Ramanathan S.,Annamalai University | Ramakrishnan V.,Thermal Systems Group
Materials and Design | Year: 2010

The need for lightweight, dimensionally stable materials for critical aerospace applications opened new frontiers of advanced materials. Metal-matrix composites can withstand the extreme conditions often encountered in space environment. The metal-matrix composites have been developed indigenously and tested in Thermo Mechanical Analyser (TMA). The measurement and characterization of thermo physical properties of MMC such as density, coefficient of thermal expansion (CTE), specific heat (Cp) and thermal conductivity plays a important role. It is essential to evaluate the new material for thermal stability and to evaluate CTE before actual use. Experimentally the CTE can be measured by TMA under the absolute methods. The experiments have been carried out in the temperature range -125°C to 550°C. The measurements of the thermal properties of materials help better understanding of the thermal design. Stir casting technique was used to fabricate the 7075 Aluminium Alloy and 7075 Al with different volume fractions of SiCp composites. The composites exhibited lower coefficient of expansion values than the alloy. © 2009 Elsevier Ltd.

Banker N.D.,Indian Institute of Science | Prasad M.,Thermal Systems Group | Dutta P.,Indian Institute of Science | Srinivasan K.,Indian Institute of Science
Applied Thermal Engineering | Year: 2010

A laboratory model of a thermally driven adsorption refrigeration system with activated carbon as the adsorbent and 1,1,1,2-tetrafluoroethane (HFC 134a) as the refrigerant was developed. The single stage compression system has an ensemble of four adsorbers packed with Maxsorb II specimen of activated carbon that provide a near continuous flow which caters to a cooling load of up to 5 W in the 5-18 °C region. The objective was to utilise the low grade thermal energy to drive a refrigeration system that can be used to cool some critical electronic components. The laboratory model was tested for its performance at various cooling loads with the heat source temperature from 73 to 93 °C. The pressure transients during heating and cooling phases were traced. The cyclic steady state and transient performance data are presented. © 2010 Elsevier Ltd. All rights reserved.

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