• S Singh

      Articles written in Bulletin of Materials Science

    • Electron microscopic studies of thermomechanically aged 2218 aluminium alloy

      Mukesh Kumar S Singh D B Goel

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      The effect of thermomechanical ageing (TMA) treatment on the microstructure and mechanical properties of 2218 Al alloy has been studied. This was followed by hardness measurements and transmission electron metallography (TEM). The 2218 Al alloy was given various thermomechanical ageing treatments including partial peak ageing, warm rolling and further ageing to peak hardness level. Without thermomechanical treatment the peak hardness value was 130 VHN. With thermomechanical treatment there was an overall improvement in hardness. This is attributed to the combined effect of dislocation precipitate networks and the fineness ofθ′ particles.

    • A cold model study of mass transfer in Q-BOP

      N Prasad S Singh S L Malhotra

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      At steel-making temperature, chemical kinetics can rarely be the rate-limiting step. Thus most of the reactions are limited by the rate of mass transfer to and from the reaction interface. The overall rate of mass transfer may be controlled by gas phase mass transfer or liquid phase mass transfer. Since in Q-BOP, the rate of reaction may be controlled by the rate of mass transfer in gas phase or in liquid phase, both were studied in a cold model. The different variables studied were tuyere diameter, jet direction, flow rate of gas and tuyere depth. The results of gas phase mass transfer indicate that the effect of tuyere diameter and jet direction is very small. For Reynolds number less than 9000 the effect of flow rate and tuyere depth is given by the equation,KgA/L0Q = 0·02d0 + 0·043, whereas for Reynolds number greater than 9000 the effect of flow rate and tuyere depth is given by the equation,KgA/L0Q=0·061d0+0·046. Similarly the liquid phase mass transfer coefficient is independent of the tuyere diameter and the shrouding gas, and is not much affected by the jet direction. The effect of gas flow rate and tuyere depth is given by the equation,KLA=0·077 (Q)0·75(L0)0·61.

    • Thermomechanical ageing (TMA) of 2014 aluminium alloy for aerospace applications

      S Singh D B Goel

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      Various thermomechanical ageing (TMA) treatments for 2014 Al-alloy have been developed which include partial peak ageing, warm rolling and further ageing to peak hardness at 160°C. Electron microscopic studies reveal that the TMA treatments affect substantially the ageing characteristics. The TMA-Ib treatment yields finestϑ′ needles having longitudinal dimensions of ∼400 Å. TMA treatment leads to precipitate-dislocation network of different magnitudes. Among the TMA treatments, the TMA IIb treatment results in thickest precipitate-dislocation tangles. In addition toϑ′, two types of dispersoids Al4CuMg5Si4 and Al12 (Fe, Mn)3Si have been observed. The density or concentration of these dispersoids is drastically reduced due to TMA treatments. Thus an optimum TMA treatment i.e. TMA-IIb has been developed which results in a significant improvement in the mechanical properties of 2014 Al-alloy.

    • Synthesis of Y-Ba-Cu-O superconducting material by citrate chemical route—some observations

      R K Kotnala S M Khullar B S Khurana K Jain M Sharma S Singh R C Goel G K Padam R B Tripathi B K Das

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      We present an overview of our powder synthesis procedure and give some initial results concerning the superconducting properties of YBa2Cu3O7−x.

    • Grain boundary effect on the electrical properties of boron-doped polysilicon films

      N K Upreti S Singh

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      The effect of grain boundary width has been accounted for and a modified simple model of average carrier concentration is presented considering the transport mechanism of charge carriers by thermionic emission only. It is found that the electrical properties of polysilicon are very sensitive to doping concentration when the grain size is small and the effect of grain boundary width on electrical properties increases as the grain size decreases. The inclusion of grain boundary width in resistivity and mobility formulae also gives better results near the critical doping concentration. The proposed model gives better agreement between experimental data and theoretical results.

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