• Volume 13, Issue 5

      December 1990,   pages  305-369

    • Preparation and characterization of aluminium alloy sheet Aramid fibre-laminated composites

      P Kanakalatha M K Sridhar Chadra Ajay C Balasingh A K Singh

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      Laminated composites consisting of alternate layers of aluminium alloy sheets and unidirectional Kevlar-49 fibre epoxy composites were prepared using two different aluminium alloys DTD 687 and aluminium-lithium alloy. Tensile, compressive and interlaminar shear strengths of the laminates were measured. The residual stresses in the aluminium alloy sheets arising out of thermal mismatch between aluminium alloys and aramid fibres were also measured. It is found that the laminates have lower density, higher tensile strength and marginally lower Young’s modulus as compared with monolithic alloy sheets.

    • Microstructure and thermomechanical pretreatment effects on creep behaviour of helium-implanted DIN 1·4970 austenitic stainless steel

      M K Matta W Kesternich

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      Microstructure investigations were carried out on unimplanted and 150 at.ppm helium implanted foil specimens of DIN 1·4970 austenitic stainless steel after various thermomechanical pretreatments. Creep tests were also carried out for both helium-implanted and unimplanted specimens at 700°C and 800°C. The strength, ductility and rupture time are correlated with the dislocation and precipitate distributions. Helium embrittlement can be reduced in these experiments when dispersive TiC precipitate distributions are produced by proper pretreatments or allowed to form during creep test.

    • Microstructures of CaSO3 0·5 H2O single crystals grown in silica gel

      S N Patil A Venkateswara Rao

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      This paper deals with the study of surface structures of silica gel grown crystals of CaSO3 0·5 H2O. Various growth features such as growth layers, overgrowths and oriented and random liquid inclusions have been observed using optical and scanning electron microscopy techniques.

    • An alternate method for determination of brittleness of ceramics and polymers

      S B Bhaduri

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      As opposed to a pendulum scratching test for the determination of brittleness parameter for ceramics and polymers, this paper proposes an alternate brittleness parameter based on indentation analysis. The important advantages are that (i) no elaborate experiments are needed, and (ii) the proposed brittleness parameter has physical implications. The proposed parameter is as effective as the pendulum test for categorizing the brittleness of ceramics and polymers.

    • 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.

    • Composition dependence of electrical properties of simultaneously evaporated Sb-Se thin films

      P S Nikam R R Pawar

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      Amorphous thin films of Sb-Se are prepared using the three-temperature method. The films are prepared with atomic compositions from 5–90 at.% Sb. The electrical resistivity, Hall voltage and thermoelectric power of annealed samples have been measured in the temperature range 25 to 250°C. On heat treatment the sharp fall of resistance of the annealed films is attributed to radical structural transformation from amorphous to crystalline. Electrical resistivity, Hall constant and thermoelectric power are found to vary with thickness and composition of the film.

    • Metallurgical characteristics of electroslag-refined MDN 250 maraging steel

      K R Udupa D H Sastry G N K Iyengar

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      MDN-250 maraging steel was electroslag-refined in a 350 kVA DC ESR unit using a slag of composition, CaF2-65, CaO-9, Al2O3-2O, TiO2-5, and MoO3-1 (wt % basis) in straight as well as reverse polarity modes of melting. The chemical homogeneity of the ingots was established by X-ray fluorescence, plasma scan and spectrovac methods. The dissolved gas content (O and N) in the ingots was determined by a LECO gas analyser. Volume fraction, density and size distribution of inclusions in the ingots and the electrode were determined in a Quantimet image analyser. These results were supplemented by EPMA and SEM studies on selected inclusions. Mechanical properties of the ingots in the heat-treated and aged conditions were assessed and compared with those of the electrode material.

      The present results confirm that the reverse polarity mode of melting is best suited for producing quality maraging steels for the ingots produced by this mode of melting were found to possess superior metallurgical characteristics in terms of cleanliness and mechanical properties compared to those produced by the straight polarity ESR route and other conventional methods.

    • A laboratory design for uniaxial hot pressing

      D S Mungekar K B Bhatt A J Singh

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      A design to hot press uniaxially compacts of 12 mm diameter and 15 mm long and its assembly has been described. The hot press was successfully employed to demonstrate conversion of BN powder into hexagonal machinable variety at 1800°C and 80 bars pressure.

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