• E S Dwarakadasa

      Articles written in Bulletin of Materials Science

    • Computer-aided composition-treatment-structure-property correlation studies in steels

      K Vijayaraju E S Dwarakadasa

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      Internal structure of materials uniquely decides their properties. The structure is a complicated function of composition and thermal and/or mechanical treatment. Inter-relation is so complex that a highly generalized correlation is very difficult. Steel is a very good example to illustrate this complexity. Advent of mini- and microcomputers have now paved way for handling such multiparametric problems in a more rational way, with greater ease and increased confidence. This paper is an attempt to develop a computer software which will assist the user in three different ways: (a) to determine the treatments that will generate a desired structure, when compositions are known; (b) to determine composition limits within which desired structure will result having defined the treatments, and (c) to predict structures that can be generated when composition and treatments are limited. This program has immense utility of (i) best use of available inventory, (ii) reduction of standards, varieties and inventory and (iii) most importantly to decide the best purchase based on treatment limitations in the shop. A large data bank is being built to support the program.

    • Failure analysis of a hot extrusion die used for Al-Li alloy processing

      U Rama Murty G S Avadhani E S Dwarakadasa

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      Al-Li alloys being developed as lighter, substitutes for conventional high strength Al alloys are to be processed by routine methods. During extrusion of a 8090 Al-Li alloy, the extrusion die container failed causing some alarm. This failed die container was analysed to examine if the failure was caused by interaction of Li diffusing out of Al-Li alloy with the carbides of die steel. The evidence, although not conclusive, is sufficient to exercise caution during such processing.

    • Effect of hydrogen charging on the mechanical properties of medium strength aluminium alloys 2091 and 2014

      Amit Bandyopadhyay Rajan Ambat E S Dwarakadasa

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      Cathodic hydrogen charging in 3·5% NaCl solution altered the mechanical properties of 2091-T351 (Al-Cu-Li-Mg-Zr) determined by a slow (10−3/s) strain rate tensile testing technique. UTS and YS decreased in the case of 2091-T351 and 2014-T6(Al-Cu-Mn-Si-Mg) with increase in charging current density. Elongation showed a decrease with increase in charging current density for both the alloys. However, elongation occurring throughout the gauge length in uncharged specimens changed over to localized deformation, thus increasing the reduction in area in charged specimens. A transition in fracture mode from surface (brittle) to the core (ductile) was observed. The presence of hydrogen increased the hardness, mostly indicative of solution strengthening and it decreased with depth confirming the existence of hydrogen concentration gradient. The effects were similar in 2014-T6, but to a slightly smaller extent.

    • Foreword

      D K Avasthi E S Dwarakadasa

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    • Effect of hydrogen in aluminium and aluminium alloys: A review

      Rajan Ambat E S Dwarakadasa

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      Susceptibility of aluminium and its alloys towards hydrogen embrittlement has been well established. Still a lot of confusion exists on the question of transport of hydrogen and its possible role in stress corrosion cracking. This paper reviews some of the fundamental properties of hydrogen in aluminium and its alloys and its effect on mechanical properties. The importance of hydrogen embrittlement over anodic dissolution to explain the stress corrosion cracking mechanism of these alloys is also examined in considerable detail. The various experimental findings concerning the link between hydrogen embrittlement and stress corrosion cracking are also discussed.

    • Studies on indentation fracture toughness on ceramic and ceramic composite using acoustic emission technique

      A K Ray G Das N K Mukhopadhyay D K Bhattacharya E S Dwarakadasa N Parida

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      This paper is aimed at investigating the acoustic emission activities during indentation toughness tests on an alumina based wear resistant ceramic and 25 wt% silicon carbide whisker (SiCw) reinforced alumina composite. It has been shown that the emitted acoustic emission signals characterize the crack growth during loading and unloading cycles in an indentation test. The acoustic emission results indicate that in the case of the composite the amount of crack growth during unloading is higher than that of loading, while the reverse is true in case of the wear resistant ceramics. Acoustic emission activity observed in wear resistant ceramic is less than that in the case of composite. An attempt has been made to correlate the acoustic emission signals with crack growth during indentation test.

    • Distribution of lead in lead-containing aluminium alloys obtained by liquid phase co-spray forming technique

      Yu Fuxiao E S Dwarakadasa S Ranganathan

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      Liquid phase co-spray forming (LPCSF) technique was employed to produce Al-Pb and Al-Si-Pb alloys to show that it is possible, using this technique, to distribute lead into very fine-sized particles in Al/Al alloy matrix at low melt temperatures. Microstructural studies were carried out to explore the mechanisms governing lead distribution in the matrix of the alloys during processing. Results showed that, regardless of the alloy compositions and experimental conditions, the microstructures of the preforms exhibited great similarity, i.e. less uniform distribution of Pb particles in the base region, and uniform distribution of fine Pb particles in the equiaxed region. During LPCSF process, the behaviour of Pb droplets was similar to that of ceramic particles, except that the shape and size of liquid Pb phase varied corresponding to local solidification condition.

    • Effect of corrosive medium on fatigue crack growth behaviour and fracture in high martensite dual phase steel

      K V Sudhakar Asim Bag E S Dwarakadasa K K Ray

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      Fatigue crack growth (FCG) behaviour in both near-threshold and higher stress intensity range (ΔK) in intercritically annealed dual-phase (DP) steel containing martensite between 32% and 76% in ferrite has been studied in 3·5% NaCl solution. It is shown that the amount of martensite content in dual phase steel has a significant effect on threshold (ΔKth) values and FCG rates. Higher content of martensite in ferrite leads to higher threshold values and lower FCG rates. Further, ΔKth is much higher in 3·5% NaCl solution as compared to that in laboratory air. Fractography studies reveal that in the near-threshold region, fracture surfaces are characterized mainly by intergranular cracking in corrosive (3·5% NaCl solution) environment. Higher threshold values in 3·5% NaCl solution is attributed to the higher crack closure induced by rougher fracture surface and by the strong wedge effects of corrosion products.

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