• R K Mandal

      Articles written in Bulletin of Materials Science

    • XRD and optical microscopic studies of Co(III) complexes containing 5-cyano-6-(4-pyridyl)-2-thiouracil, thymine and adenine bases

      Lallan Mishra Brajesh Pathak R K Mandal

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      Multifunctional ligand 5-cyano-6-(-4-pyridyl)-2-thiouracil (L) was prepared and allowed to react with trans [Co(en)2Cl2]+Cl resulting into [Co(en)2LCl]2+.2Cl which upon further reaction with equimolar ratio of ligand [L] gave the complex [Co(en)2L2]3+.3Cl. These metal complexes were then separately reacted with thymine and adenine bases. Complexes thus prepared after characterization by their elemental analysis, FAB mass and spectral (IR, 1HNMR, UV-visible) data were studied for their powder X-ray diffraction and optical microscopic characteristics.

    • Non-equilibrium solidification of undercooled droplets during atomization process

      Prashant Shukla R K Mandal S N Ojha

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      Thermal history of droplets associated with gas atomization of melt has been investigated. A mathematical model, based on classical theory of heterogeneous nucleation and volume separation of nucleants among droplets size distribution, is described to predict undercooling of droplets. Newtonian heat flow condition coupled with velocity dependent heat transfer coefficient is used to obtain cooling rate before and after nucleation of droplets. The results indicate that temperature profile of droplets in the spray during recalescence, segregated and eutectic solidification regimes is dependent on their size and related undercooling. The interface temperature during solidification of undercooled droplets rapidly approaches the liquidus temperature of the alloy with a subsequent decrease in solid–liquid interface velocity. A comparison in cooling rates of atomized powder particles estimated from secondary dendrite arm spacing measurements are observed to be closer to those predicted from the model during segregated solidification regime of large size droplets.

    • Surface hardness behaviour of Ti–Al–Mo alloys

      Raja Ram Prasad Shankar Azad A K Singh R K Mandal

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      The microhardness characteristics of various micro-constituents formed in the Ti–Al–Mo alloys have been investigated. Four alloys having compositions, Ti–40Al–2Mo, Ti–42Al–2Mo, Ti–40Al–6Mo and Ti–42Al–6Mo, have been chosen for this purpose. All of these were heat treated at 1300°C and 1400°C for 1 h and water quenched. All the specimens after above heat treatments have displayed load independent Vickers hardness values (VHN) around 300 g of applied load. The average surface hardness characteristic of the alloys is largely found to be dictated by the phases that are present. The microstructural specific VHN values vary between 600 and 750. The indentation behaviour, however, is governed by the morphologies and length scales of microstructures. The most remarkable finding of the present study pertains to the formation of shear bands around the periphery of the indenter for a finer basket weave microstructure in the Ti–40Al–2Mo. The cluster of finely located slip steps was clearly seen. Such a report is lacking in literature in this class of alloys.

    • Effect of thermomechanical processing on evolution of various phases in Ti–Nb alloys

      S Banumathy K S Prasad R K Mandal A K Singh

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      This paper deals with the effect of thermomechanical processing on microstructural evolution of three alloys, viz. Ti–8Nb, Ti–12Nb and Ti–16Nb. The alloys were hot rolled at 800°C and then subjected to various heat treatments. Samples from hot-rolled alloys were given solution-treatment in 𝛽 and 𝛼 + 𝛽 phase fields, respectively followed by water quenching and furnace cooling. The solution-treated alloys were subsequently aged at different temperatures for 24 h. Phases evolved after various heat treatments were studied using X-ray diffractometer, optical, scanning and transmission electron microscopes. The alloy Ti–8Nb exhibits 𝛼 and 𝛽 phases while the alloys Ti–12Nb and Ti–16Nb show the presence of 𝛼'', 𝛽 and 𝜔 phases in the as-cast and hot-rolled conditions. The 𝛽 solution treated and water quenched specimen of the alloy Ti–8Nb displays 𝛼'' phase while the alloys Ti–12Nb and Ti–16Nb exhibit 𝛼'', 𝛽 and 𝜔 phases. The alloy Ti–8Nb shows the presence of 𝛼, 𝛽 and 𝜔 phases while those of Ti–12Nb and Ti–16Nb display the presence of 𝛼, 𝛼'', 𝛽 and 𝜔 in 𝛼 + 𝛽 solution treated and water quenched condition. The observation of 𝜔 phase in solution treated condition depends on the cooling rate and the Nb content while in the aged specimens, it is governed by aging temperature as well as the Nb content.

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