• Volume 16, Issue 1

      February 1993,   pages  1-85

    • Mechanical alloying—a novel synthesis route for amorphous phases

      B S Murty

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      Mechanical alloying (MA) pioneered by Benjamin is a technique for the extension of solid solubility in systems where the equilibrium solid solubility is limited. This technique has, in recent years, emerged as a novel alternate route for rapid solidification processing (RSP) for the production of metastable crystalline, quasicrystalline, amorphous phases and nanocrystalline materials. The glass-forming composition range (GFR), in general, is found to be much wider in case of MA in comparison with RSP. The amorphous powders produced by MA can be compacted to bulk shapes and sizes and can be used as precursors to obtain high strength materials. This paper reports the work done on solid state amorphization by MA in Ti-Ni-Cu and Al-Ti systems where a wide GFR has been obtained. Al-Ti is a classic case where no glass formation has been observed by RSP, while a GFR of 25–90 at.% Ti has been obtained in this system, thus demonstrating the superiority of MA over RSP. The free energy calculations made to explain GFR are also presented.

    • Plasma spraying of an indigenous yttria stabilized zirconia powder prepared by the sol-gel technique

      S V Joshi M P Srivastava M Chatterjee J Ray A Chatterjee D Ganguli

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      An indigenous sol-gel derived yttria-partially stabilized zirconia (Y-PSZ) powder has been characterized and its suitability for plasma spraying applications evaluated. The powder, determined to have about 5·1% yttria content, predominantly consisted of spherical particles with an average equivalent particle diameter close to 25µm. Furthermore, it was found that the powder did not contain any particles >50µm, which is considered the ideal upper size limit for spray-grade ceramic powders in order to ensure complete melting during spraying. The sol-gel produced powder exhibited good flow characteristics and the plasma sprayed coatings developed using this powder were also found to have excellent thermal shock resistance. The corresponding results obtained using an imported Y-PSZ powder are also presented for the purpose of comparison.

    • Electromagnetic fields near metal surfaces

      R K Thapa P Das N Kar R A Lal

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      Electromagnetic field variation at the surface region of nearly free electron metal (Al), noble metal (Ag) and transition metals (Cr, Rh, Pd and Mo) are studied with respect to the incident photon energy. The electromagnetic field used is the one calculated by Bagchi and Kar using the local frequency dependent dielectric response function. The results so obtained may be of significance in the photoemission scattering cross-section calculations in understanding electronic structure and properties of these metals.

    • Phase transition in copper(II) pyrovanadate

      N Suresh Rao O G Palanna

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      A new phase Cu2V2O7 synthesized, exhibits phase transitions between 475°C and 500°C. These phase transitions are reversible with ease in contrast toαβ phase transition at 712°C of Cu2V2O7 phase reported earlier. These phase transitions are identified by DTA technique and characterized by detailed XRD investigations at different temperatures. The crystal structures of these Cu2V2O7 phases are related to either thortveitite (Sc2Si2O7) type or a modification of it.

    • SIMS depth profiling of implanted helium in Al-Mn alloy using CsHe+ molecular ion detection

      A K Tyagi K G M Nair K Krishan

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      The use of Cs+ primary ions in conjunction with the detection of CsHe+ molecular ions is proposed for the analysis of helium in metals by secondary ion mass spectrometry (SIMS). Concentration depth profiles of helium implanted at 100keV in Al60Mn40 alloy have been measured. Helium concentrations down to about 100 ppm were measured at moderately low sputtering rate of 0·5nm/sec. The experimentally determined implantation profile of helium is compared with the theoretical profile obtained using the Monte Carlo Code TRIM.

    • Some electrical and magnetic properties of γ-Fe2O3

      A Venkataraman

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      γ-Fe2O3 synthesized from FeC4H4O4·4H2O has been studied using various techniques. The phase transformation observed by electrical conductivity measurements agrees well with the initial magnetization measurement. The magnetic hysteresis values compare with those ofγ-Fe2O3 samples synthesized using established procedures.γ-Fe2O3 particles obtained were circular in shape showing a well resolved six narrow bands in Mössbauer spectrum. The presence of hydrogen ferrite phase was also confirmed by electrical and magnetic measurements.

    • Photoconductive and ellipsometric studies of spray pyrolysed CdS thin films

      A G Valyomana Sunny Mathew K P Vijayakumar C Purushothaman

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      The influence of annealing temperature on photoconductivity of spray pyrolysed CdS films has been investigated. The annealing of films at 373K resulted in maximum photoconductivity. The photoconductivity at all wavelengths was found to decrease with increase of annealing temperature and became a minimum at 473K. For films annealed at or above 523K, the photoconductivity for wavelengths ⩾560 nm decreased considerably. The results are discussed with the help of ellipsometric data, visible and IR spectra of these samples. Also the variation in photoconductivity of these samples were studied during heating to analyse the effect of trapping.

    • On the tensile creep behaviour of a directionally-solidified Ni3Al-based alloy

      M S Gopala Krishna M C Pandey

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      High temperature tensile creep behaviour of a directionally-solidified Ni3Al-based alloy is presented. The study involved selection of nine alloy systems based on Ni3Al. The alloys contained varying amounts of Cr and Ta, fixed amounts of 1·5 at.% Hf and 0·5 at.% Zr and doped with 0·2 at.% each of C and B. The alloys were vacuum arc-melted into buttons and homogenized at 1050°C for 68 h. The test pieces of the alloys were hot compression tested at 600, 700, 800 and 900°C. The yield strength data of some of the alloys were superior to conventionally cast Mar-M 200, a cast nickel-base superalloy widely used in gas turbine structural applications. The best alloy system was chosen based on consistent performance in the hot compression studies. The alloy so chosen was directionally solidified and vacuum-homogenization-treated for 20 h at various selected temperatures. Optimum creep properties were observed at 1120°C, 20 h treatment. The minimum creep rate data of the DS alloy showed relatively higher values even at lower temperatures and stress levels as compared to Mar-M 200. Hence, the alloy is less promising in replacing nickel-based superalloys used as structural materials in gas turbine applications.

    • Studies on certain wood-plastic-composites prepared by gamma irradiation

      P T Thomas B R S Babu K Neelakandan

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      Wood-plastic-composites have been prepared using locally available soft wood and commercial monomers by vacuum impregnation of monomer in wood and subsequent polymerization by gamma irradiation. The irradiation was performed by means of a60Co source of strength 50,000 Ci at 0·2 Mrad/h. The radiation dosage required for maximum conversion of monomer into polymer was less than 2 Mrad except styrene which required a much larger dose of about 10 Mrad. The impregnation efficiency was found to be more for wood with high pore volume. The impregnation efficiency also depended on the ambient pressure: the more the vacuum, the more was the impregnation efficiency. Mechanical strength of the composites was found to be enhanced and water absorption considerably reduced. X-ray diffraction studies showed that the crystallinity of the cellulose did not get affected by the radiation polymerization which suggested that grafting of polymer on to the cell wall took place only in the amorphous regions.

    • Concise encyclopedia of magnetic and superconducting materials, 1992, (ed.) Jan Evetts - (Oxford: Pergamon Press), pp. 726, Price £ 140/$280

      C N R Rao

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