• Volume 18, Issue 4

      August 1995,   pages  309-468

    • Foreword

      Saburo Nagakura

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    • Computer simulation of deformation and fracture of small crystals by molecular dynamics method

      Masao Doyama

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      Body-centred cubic iron whiskers having [100] and [110] axes were pulled in a molecular dynamics simulation using a supercomputer. The upper yield stress close to the theoretical strength was found. Above the upper yield stress, phase transformation was observed; at the same time the stress was greatly reduced. A new possible mechanism of twinning is proposed. The whiskers were pulled until they had broken into two pieces. Copper small crystals with and without a notch were sheared. It was observed that the edge dislocations were created at the surface and moved through and escaped from the crystals. Copper small single crystals with a notch were pulled. A half-dislocation was created near the tip of the notch. Sharp yield stress was observed. In medium deformation dislocations on different slip planes were created. Due to the cutting of dislocations the tensile stress increased.

    • Basic studies leading to the development of an ultrahigh strength, high fracture toughness low-alloy steel

      G Malakondaiah M Srinivas P Rama Rao

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      Ultrahigh strength steels have been used increasingly in recent years for critical aircraft and aerospace structural applications. In such applications, though materials performance is of prime consideration, cost and availability makes the low-alloy steels an attractive option. This paper describes the development of an ultrahigh strength NiSiCrCoMo low-alloy steel, supported by significant findings obtained from the basic studies that were aimed at understanding how solute additions influence fracture resistance of iron, with and without the presence of carbon. The results of the basic studies, in combination with the work of Garrison (1986) on a NiSiCr steel, have profitably been employed in the development of a NiSiCrCoMo low-alloy steel possessing a strength-toughness combination quite comparable to the highly alloyed 250-grade maraging steel. Reproducibility of attractive strength and toughness properties has been established in tonnage scale melts. This steel, in the softened condition, has good formability and machinability. Weld parameters have also been established. The NiSiCrCoMo low-alloy steel thus meets the requirements of performance and cost rendering it an attractive option for advanced structural applications.

    • MOVPE growth and characterization of ZnSe-GaAs heterovalent heterostructures

      Mitsuru Funato Shizuo Fujita Shigeo Fujita

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      ZnSe-GaAs heterovalent heterostructures were fabricated by metalorganic vapour phase epitaxy and characterized structurally and electrically. A study on growth behaviour of GaAs on ZnSe revealed that either the 2-dimensional or the 3-dimensional growth mode may occur depending on the growth conditions. This growth behaviour is applied to the construction of low-dimensional structures. Successful fabrication of quantum well structures and GaAs islands buried into ZnSe is demonstrated by means of X-ray diffraction and transmission electron microscopy. The electrical properties of the heterostructures are also described.

    • On the stability of intermetallic phases

      S Lele B N Sarma A Ghosal G V S Sastry

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      A general methodology using atomic clusters is applied to three problems connected to the study of alloy phase stability. The cluster method proposed by Allen and Cahn is applied to non-ideal hcp structures under tetrahedral approximation using multiatom interactions. The possible ground-state structures which are stable at absolute zero temperature are obtained. A geometrical representation in 4D parameter space of the possible strengths of multiatom interactions permitted for these structures is illustrated in terms of a 2D analogue. Extending these ideas, the cluster variation method (CVM) proposed by Kikuchi is applied to fcc structures under tetrahedral approximation to find the effect of multiatom interactions on the topology of the coherent phase diagrams in which all the phases present are derivable by mere rearrangement of atoms on the parent disordered structure. In addition, the possible invariant reactions are identified in such coherent phase diagrams. Finally the CVM is applied for calculating a model incoherent phase diagram, that of Ti-Zr system, where disordered hcp and bcc phases are present. The free energies of hcp and bcc phases are formulated using CVM procedures respectively under tetrahedral-octahedral and tetrahedral approximations. The CVM is shown to be in better agreement with the thermodynamic data and to be able to reproduce the correct value of measured enthalpy of transformation compared to that given by the regular solution model, which significantly overestimates the same.

    • Novel concept for the aggregation structure of fatty acid monolayers on the water surface and direct observation of molecular arrangements in their monolayers

      Tisato Kajiyama Taishi Kuri

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      The aggregation structure of fatty acid monolayers on water subphases of different pH’s was investigated by means of transmission electron microscopy. Fatty acid monolayers exhibited the phase transition from an amorphous state to a crystalline one by surface compression in the case of a highly dissociated state of hydrophilic groups, whereas they did not show the phase transition in the case of a slightly dissociated state. The aggregation structure of monolayers on the water surface was systematically classified into “the crystalline monolayer”, “the amorphous monolayer” and “the compressing crystallized monolayer” with respect to thermal and chemical (intermolecular repulsive) factors.

      Molecular-resolution images of fatty acid molecules in the monolayers on mica substrate were successfully observed with an atomic force microscope (AFM) for the first time. The AFM image of a lignoceric acid monolayer prepared at a surface pressure of 5mNm−1 showed a two-dimensional periodic structure with locally disordered molecular arrangements. Also, the nondestructive AFM image observation was successful for a stearic acid monolayer which was prepared by a multistep creep method, indicating that a high mechanical stability of the monolayer is inevitably required for the nondestructive AFM observation.

    • Some recent advances in bulk growth of mercury cadmium telluride crystals

      R K Sharma R K Bagai Vikram Kumar

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      The inherent metallurgical problems associated with the HgTe/CdTe pseudobinary alloy system render the standard crystal growth processes inapplicable to the preparation of mercury cadmium telluride crystals for infrared detector applications. A variety of rather nonconventional techniques have been developed to overcome these problems. Two such techniques, viz. asymmetrical Bridgman and horizontal casting for solid-state recrystallization, developed at Solid State Physics Laboratory for the bulk growth of mercury cadmium telluride crystals are reviewed in this communication.

      Due to the poor thermal conductivity of mercury cadmium telluride melts and solids, and the use of thick-walled quartz ampuoles, it is extremely difficult to obtain a flat solid-liquid interface during Bridgman growth of this material. The technique of asymmetrical Bridgman has been successful in overcoming this problem to a great extent. Solid-state recrystallization has been widely accepted as one of the most successful techniques for obtaining large quantities of acceptable-quality mercury cadmium telluride crystals for infrared detector applications. This is a two-step process—the melt is first quenched to obtain a good cast, which is then subjected to a grain-growth annealing. The horizontal casting procedure developed for solid state recrystallization growth has been successful in improving the overall quality and yield of bulk mercury cadmium telluride crystals.

    • Recent studies on electrical and magnetic properties of molecular solids

      Yusei Maruyama

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      Recent progress in studies on electrical and magnetic properties of some typical molecular solids is described, focussing on research in Japan. Especially we focus on two recent topics, organic semiconductor BTQBT and organic superconductors. Two types of compound are discussed, (BEDT-TTF)2Cu(NCS)2 and M3C60 (M = K or Rb). Finally, two kinds of molecular ferromagnet, nitronyl nitroxide radicals and C60(TDAE), are briefly introduced.

    • Interfaces in discontinuously reinforced metal matrix composites: An overview

      R Mitra Y R Mahajan

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      The fundamental and engineering aspects pertaining to the matrix-reinforcement interfaces in discontinuously reinforced metal matrix composites are presented in this overview. The interfaces play a key role in determining mechanical properties, namely Young’s modulus, yield strength, elongation, creep and fracture behaviour, as well as physical properties like coefficient of thermal expansion, thermal conductivity and damping characteristics of metal matrix composites; these are discussed in detail. The ratio of the experimental value of the Young’s modulus to that predicted from the rule of mixtures has been used as a measure of interfacial bond strength. Various issues such as the nature of the interfacial bond, chemical reaction at the interfaces, and effect of alloying and processing on the structure of the interfaces and the properties of the composite are examined. In order to exploit the full potential of reinforcing the metallic matrix, the suggested strategies include creation of metallic bonding at the interface, use ofin situ processing, choice of right type of alloying elements, and heat treatments and engineering of interfaces.

    • Crystal engineering of high-Tc and related oxide films for future electronics

      Hideomi Koinuma

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      Advanced technology and future prospect of oxide-based electronic materials are described with a focus on the significance of atomically controlled epitaxy of high-Tc superconductors and related oxide films. Problems in suitably forming the oxides whose power is potentially superior to silicon’s are discussed to stimulate technology development for engineering oxide film growth on an atomic scale. Our experimental results on controlled epitaxial growth of oxide films are presented with respect to pulsed laser deposition of YBa2Cu3O7 −δ films as well as laser MBE growth of SrTiO3 homoepitaxy and CeO2 heteroepitaxy on Si substrates.

    • Use of microwaves for the synthesis and processing of materials

      K J Rao P D Ramesh

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      An overview of the synthesis of materials under microwave irradiation has been presented based on the work performed recently. A variety of reactions such as direct combination, carbothermal reduction, carbidation and nitridation have been described. Examples of microwave preparation of glasses are also presented. Great advantages of fast, clean and reduced reaction temperature of microwave methods are emphasized. The example of ZrO2-CeO2 ceramics has been used to show the extraordinarily fast and effective sintering which occurs in microwave irradiation.

    • Book review

      K J Rao

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    • Announcement

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      Posted on July 25, 2019

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