• P K Ghosh

      Articles written in Bulletin of Materials Science

    • Use of linear weight factor in real-space renormalization group

      D Sengupta P K Ghosh

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      An important problem in all real space renormalization group calculations is the choice of appropriate weight factor for different configurations. In this context, the use of linear weight factor has been restricted due to lack of suitable criterion for selecting the parameterq. An elegant matching procedure has recently been developed to fixq. First we undertake a systematic investigation of the variation of critical constants with cell size. A comparison is also made with the results obtained using an earlier criterion proposed by Subbarao. Secondly, we extend the applicability of the theory to the realm of dynamic problems by studying the exponent of energylike perturbation in 2D Glauber-Ising model. The value of the exponent obtained for square and triangular lattices are 2·147 and 1·918 respectively which are in good agreement with the general consensus (∼2·0).

    • Surface composition and near-surface hardness studies on high dose boron-implanted 304 stainless steel

      A K Goel N D Sharma R K Mohindra P K Ghosh M C Bhatnagar

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      The modification of boron-implanted near surface of 304 stainless steel having strained and strain-free surfaces was studied. The energy of the boron ion was 130 keV at a dose of 2·5×1017 ions cm−2. Ion-implantation is known to modify the tribological properties of metals, however, it is not well-understood as to how such a shallow implanted layer can affect the microhardening. A full understanding of the process involved is yet to emerge. In the present work the ion implanted layer was characterized for boron depth profiles using AES and XPS. The implanted layer is observed to contain B2O3, Fe2B, FeB and CrB2 compounds with small fractions of chromium and iron oxides. The strain-free surface of 304 SS shows an increase in microhardness by ∼ 80% after boron ion implantation at 2 gf and the strained surface by ∼ 30% at the same load. The annealing effects on microhardness for mechanically polished and implanted samples were also investigated in the temperature range 100 to 400°C. The possible correlation of near-surface microhardness increase with boride formation is discussed.

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