• Volume 15, Issue 6

      December 1992,   pages  481-564

    • Foreword

      P Rama Rao K J Rao P Ramachandrarao S Ranganathan

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    • Metallic structures: A magnificent obsession

      T R Anantharaman

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      The twentieth century has been an exciting and fruitful period for materials scientists involved in probing the structure of metals and alloys at different levels. The Science of Metallography dealing with the macrostructure, microstructure, submicrostructure and crystal structure of metallic materials has made impressive strides in many directions during this century, particularly during the last four decades coinciding with the author’s own research career. The steady advances in optical microscopy, the growing sophistication in electron microscopy and diffraction, the welcome advent of field ion microscopy, the increasing precision in X-ray diffractometry and the powerful back-up provided by Computer Science have all combined to open out many a new and bright vista in Structural Metallurgy in recent decades.

      In this lecture some of the notable developments in the fascinating area of metallic structures are highlighted with special reference to the researches of the author, his students and coworkers in several Indian and overseas Laboratories, particularly Oxford (UK), Stuttgart (Germany), Pasadena (USA) and Bangalore, Varanasi and Patiala (all three in India).

    • Rapid solidification of steels

      P Ramachandrarao

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      Solidification at very high rates of cooling results in considerable refinement in the microstructure of alloys. It enables the formation of extremely fine grains, extends solid solubilities and leads to the nucleation of many metastable crystalline phases. We discuss briefly the methods of rapid solidification and their impact on microstructure and structure of alloys. Each of the aspects of structure development is illustrated with examples from steels.

    • Nanocomposites by rapid solidifcation route

      K Chattopadhyay

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      Nanometric aggregates of solids can be classified into two types, nanograined or nanophased materials and nanocomposites. In the present paper after a brief review including the relation between size and boundary fraction, the basic principles that can be utilized to synthesize these materials from liquid route has been discussed. We shall present examples to show that with proper choice of systems and conditions it is possible to obtain nanocomposites in systems showing clustering tendencies in liquid as well as the systems exhibiting ordering tendencies leading to compound formation.

    • Spray forming: Science and technology

      S N Ojha

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      Spray forming involves sequential gas atomization of a melt into a spray of fine droplets and their deposition on a substrate to build up a high-density preform. The rapid solidification inherent in spray deposition generates refined, equiaxed and low segregation microstructures. A number of promising features of this near-net shape manufacturing process are highlighted and compared, wherever possible, with the conventional casting and PM techniques. Some commercial nozzles used to create spray and mechanisms associated with spray generation are described. The consolidation of the droplets and the development of the microstructure in the deposit are primarily governed by the nature of the spray and the thermal state of droplets on the deposition surface. Several microstructural characteristics of the deposit are presented and their origin in spray deposition is discussed.

    • Rapid solidification of zirconium-based alloys

      G K Dey S Banerjee

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      Zr based metal-metal binary and ternary alloys can be obtained in the amorphous state in very wide composition ranges. Several eutectic reactions and intermetallic compounds are present in these alloy systems which provide opportunities for examining the validity of different theories on glass formation. The amorphous phases in these alloys decompose by a variety of crystallization mechanisms. Instances of polymorphic, primary and eutectic crystallization have been encountered in these glasses. Zr-based metallic glasses possess excellent corrosion resistance and mechanical properties. In several studies their properties have been compared with that of their crystalline counterparts and interesting differences have emerged. In the solute lean Zr-based alloys very large freezing ranges are available for studying the liquid to solid transformation. It has been possible to study the formation of some of the low temperature phases directly from the liquid. This paper describes some of the aforementationed studies carried out on Zr-based amorphous and crystalline alloys.

    • Some amorphous alloys in Zr-Ru-Mo and Zr-Ru-W systems prepared by rapid solidification

      D Gusković Z D Stanković D Marković

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      All binary systems of the ternary systems Zr-Mo-Ru and Zr-W-Ru show at least one eutectic point. This indicates the existence of low melting eutectic alloys in these ternary systems (∼ 1200–1300°C). As starting materials, homogeneous Zr-Mo-Ru and Zr-W-Ru samples of different compositions were prepared by rapid solidification (∼106Ks−1) in a splat-cooling apparatus with a rf levitation coil and a high-velocity two-piston arrangement driven by solenoids. The possibility of obtaining alloys in amorphous state from low-melting areas of these ternary systems with the addition of boron or silicon has been investigated.

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