• A K Sinha

      Articles written in Bulletin of Materials Science

    • Surface alloying of pure iron by molybdenum and tin by a continuous wave CO2 laser

      I S Batra K Bhanumurthy S K Khera A K Sinha A R Biswas V I Titov M B Ignatiev A Uglov

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      It is now well established that considerable improvement in the mechanical/chemical properties of near surface regions of materials can be achieved by the process of laser surface alloying. The change in chemistry at the surface is attained through the process of melting and mixing of a predeposited coating and a thin layer of the substrate. Rapid solidification of this molten region at the surface then results in the development of very interesting microstructural features. In the present work, an attempt was made to surface alloy pure iron by molybdenum and/or tin by using a continuous wave CO2 laser. Morphology of the resulting microstructural features was examined by optical as well as scanning electron microscopy and the compositional details were determined using an electron probe microanalyser. Microhardness measurements were carried out as a function of depth from the laser-treated surface. This paper discusses the results of these investigations and delineates the roles of the various parameters on the chemistry and microstructure of the surface alloys formed as a result of laser treatment.

    • Micro hardness measurements on lead silicate glass

      V K Shrikhande T Mirza B B Sawant A K Sinha G P Kothiyal

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      The synthesis of lead silicate glass suitable for fabrication of compression type glass to metal seals has been studied with varying amounts of modifier ions (Na, K and Ba). A three-stage heating schedule was evolved for the preparation of glass. While, some of the constituents were taken in the form of oxides, the others were either in the form of carbonates or nitrates. Dependence of micro hardness of these glasses on the relative content of Na2O, K2O and BaO was investigated. The concentration of these oxides was varied in the range 0–16 wt%. The modifier ions were seen to affect the micro hardness in a combplex manner. While the micro hardness of glass without Na2O and 13 wt% K2O was found to be 504 kg/mm2, it turned out to be 547 kg/mm2 for a glass with 13 wt% of Na2O in the absence of K2O. However, the micro hardness of the glass synthesized having optimum composition with oxides of Na, K and Ba in the proportion of 5, 8 and 4 wt%, respectively was 455 kg/mm2. The glass powder was found to be suitable for making single- and multi-pin seals which could withstand pressures up to 1·2×104 psi and vacuum of 10−8 Torr.

    • Structural studies of Nd$_{1.85}$Ce$_{0.15}$CuO$_{4}$ $+$ Ag superconducting system

      N RADHIKESH RAVEENDRAN A K SINHA R RAJARAMAN M PREMILA E P AMALADASS K VINOD J JANAKI S KALAVATHI AWADHESH MANI

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      We have studied for the first time the effect of Ag addition (0–15 wt%) to the superconducting system, Nd$_{1.85}$Ce$_{0.15}$CuO$_{4}$, on its crystal structure and local structural features, using synchrotron X-ray diffraction(SXRD) and Raman spectroscopy, respectively. SXRD and subsequent Rietveld refinement studies on powders of Nd$_{1.85}$Ce$_{0.15}$CuO$_4$ $+$ Ag system indicate a small but significant change in lattice parameter upon Ag addition, showing evidence for possible incorporation of Ag to the extent of $\sim$1 wt%. Raman spectroscopic studies indicate that the parent structure of Nd$_{1.85}$Ce$_{0.15}CuO$_{4}$ remains unaffected with no major local structural changes on doping with silver. However, all Raman modes show minor phonon hardening upon Ag addition, which is consistent with the unit cell volume reduction as is observed in XRD. A systematic bleaching out of the apical oxygen defect mode was also observed with increased Ag addition. Polarized Raman measurements helped to identify the asymmetric nature of the B1g Raman mode. X-ray diffraction studies on pellets of Nd$_{1.85}$Ce$_{0.15}CuO$_4$ $+$ Ag system further indicate a randomization of preferred orientation upon Ag addition. The superconductivity of the Nd$_{1.85}$Ce$_{0.15}$CuO$_4$ $+$ Ag system has been well characterized for all the compositions studied.

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