Articles written in Bulletin of Materials Science
Volume 6 Issue 3 July 1984 pp 537-547
The methods of characterization of different types of radiation-induced defect clusters by
It is shown that the formation of disordered zones resulting from displacement cascades in the ordered matrix can be utilized in determining the shape and the volume of cascades in the virgin state. The importance of different contributing factors like the strain contrast and the structure factor contrast in producing the overall contrast from the disordered zones is discussed. Detailed observations on the shape of the disordered zones are shown to be important to establish the occurrence of the replacement collision sequence and the formation of sub-cascades.
Volume 6 Issue 4 September 1984 pp 701-701
Majority of the metallurgical phase transformations are first-order transitions which occur by the nucleation and growth process near equilibrium conditions. In recent years, homogeneous transformation has been reported in some of these cases at conditions significantly away from those of equilibrium. In this paper some of these transformations will be discussed. In the first part of the presentation the thermodynamic and the mechanistic distinctions between first and higher order phase transformations will be discussed and a comparison made between homogeneous and heterogeneous modes of phase transformations and those of deformation. Based on Landau’s free energy
Volume 14 Issue 4 August 1991 pp 1135-1140 International Conference On Superconductivity—III
Fast-acting energy storage devices can effectively damp electromechanical oscillations in a power system, because they provide storage capacity in addition to the kinetic energy of the generator rotor, which can share the sudden changes in power requirement. The present paper explores the means of reducing the inductor size for this application so that the use of high-
Volume 15 Issue 4 August 1992 pp 289-296
Texture plays an important role in the commercial acceptability of Zr-2·5 wt% Nb pressure tubes used in nuclear reactors. A modified flow sheet for the fabrication of these pressure tubes involves a few additional steps viz. stress relieving, cold working and annealing, as compared to the conventional route. The evolution of texture during sequential fabrication steps of extrusion, stress relieving, cold working and annealing was studied in terms of texture coefficients and inverse pole figures. It was observed that crystallographic texture primarily developed during hot extrusion and the additional steps of stress relieving, cold working and annealing did not alter the texture significantly. The texture developed was one having a majority of the basal plane normals along the tangential direction of the tube.
Volume 15 Issue 6 December 1992 pp 543-556 Symposium Session On Rapid Solidification Processing
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.
Volume 16 Issue 5 October 1993 pp 347-356
The application of self-propagating high-temperature synthesis (SHS) to prepare a few borides of titanium was investigated. Using the plane wave propagation mode, the synthesis of titanium borides in the cold-pressed cylindrical specimens of the component powder mixtures was effected and was studied as a function of boron content in the initial mix and the specimen size. SHS reaction in compacts having diam. of 6 mm or less and high bulk density could not be initiated and/or sustained and was considered to be a result of rapid heat dissipation.
Volume 17 Issue 5 October 1994 pp 505-511
We report Raman scattering and photoluminescence studies on porous silicon film formed on n-type silicon. The Raman spectra over the sample surface exhibit considerable variation whereas the photoluminescence spectra are practically identical. Our results indicate that, well inside the film surface, it consists of spherical nanocrystals of typical diameter ≈ 100Å, while on the edge these nanocrystals are ⩾ 300Å. We further observe that there is no correlation between the photoluminescence peak position and the nanocrystal diameter. This suggests that the origin of the photoluminescence is due to radiative recombination between defect states in the bulk as well as on the surface of the nanocrystal.
Volume 17 Issue 5 October 1994 pp 533-550
Room-temperature visible luminescence observed in porous silicon is one of the most significant discoveries of this decade as it opens up the possibility of silicon-based optoelectronics afresh. The exact mechanism of this different luminescence behaviour of porous silicon, compared to crystalline silicon, is not well established. In this paper results of a combination of infrared absorption, and photoluminescence emission and excitation spectroscopies will be described to show that the nanocrystallite nature of porous silicon and chemical environment at the surface are the important aspects of this novel luminescence behaviour.
Volume 17 Issue 6 November 1994 pp 875-881
The present work reports the results on the deformation behaviour of ZrO2-3 mol% Y2O3 (3Y-TZP) ceramics which were prepared by pressureless sintering at 1400°C. Dense, cylindrical samples were subjected to uniaxial compression tests under a constant stress of 15 MPa in the temperature range of 1200–1400°C. The ceramics exhibit considerable ductility, attaining over 60% true strain without any edge cracking. Microstructural changes due to interaction of grain boundary viscous phase with the ultrafine and equiaxed grains were analyzed by transmission electron microscopy. Results show the grain boundary sliding accompanied by a diffusion accommodation process as the predominant deformation mechanism in these ceramics.
Volume 17 Issue 6 November 1994 pp 893-910
Fatigue cracked and fast fractured regions in four-point bend specimens prepared from 25 wt% silicon carbide whisker reinforced alumina composite were examined by scanning electron microscopy. This composite was found to be susceptible to a fatigue crack growth phenomenon similar to that in the case of metallic materials, but with a higher crack growth exponent. In the fatigue region, the alumina matrix failed mainly in a transgranular mode and the whiskers mainly failed with a flat fracture surface but without their pullout. On the other hand, in the fast fracture region, the whiskers failed predominantly by pullout and the alumina matrix failed in a mixed mode with about half in transgranular and the other half in intergranular mode. Thus, to improve the fracture toughness of the material, the grain boundary strength of alumina and the matrix whisker interfacial bonding should be improved. To increase the resistance to fatigue, the fracture strength of the alumina grains should be improved by using finer α-alumina particles and the fatigue strength of the whisker have to be increased by improving the uniformity in distribution of β-SiC whiskers during hot pressing.
Volume 20 Issue 4 July 1997 pp 531-534
We report measurement of the electrical resistivity
Volume 20 Issue 4 July 1997 pp 541-548
In this paper, we have examined different types of interfaces that occur between orientational/translational variants generated during the ordering process. This has been illustrated citing examples of ordering of the FCC structure into DO22, Dla and Pt2Mo type structures in some nickel base alloys. Microstructures consisting of more than one ordered structure have also been investigated. Superlattice domains of DO22 and Pt2Mo type structures have also been found to coexist in a microscopic scale of mixing in Ni-V alloys while mixed domains of Dla and Pt2Mo type structures on a much finer scale have been observed in Ni-Mo alloys. The formation of different variants (rotational and translational) of ordered structure(s) from the disordered lattice has been explained on the basis of group theoretical and symmetry considerations.
Volume 20 Issue 5 August 1997 pp 623-635
In 1973, Usikov and Zilbershtein proposed that the
Volume 20 Issue 6 September 1997 pp 787-803 India-Japan Seminar On New Materials
An extensive amount of experimental work has been reported in the literature on the ordering behaviour of Ni-Mo alloys containing 8–33 at% of Mo, which exhibit both short-range and long-range ordering phenomena and a competition among several fcc-based long-range ordered structures. We have used local-density-based tight binding linear muffin-tin orbital (TB-LMTO) method in conjunction with ‘augmented space recursion + orbital peeling’ (ASR + OP) for the determination of ground state energies of these superstructures in terms of effective pair interactions up to the fourth nearest neighbour pairs. The ordering behaviour of the four competing fcc-based superstructures has been studied using the mean-field-based ‘static concentration wave’ (SCW) model in terms of the free energy-order parameter plots (Landau plots) and the free energy-composition plots. The instability domains with respect to concentration fluctuations, both short wavelength (ordering) and long wavelength (clustering) have been identified from these calculations. This information has been used to predict the sequence of transformation events in the Ni-Mo alloys undergoing ordering and/or clustering and the results are compared with those obtained experimentally.
Volume 22 Issue 3 May 1999 pp 701-708 Characterization Of Materials
High resolution electron microscopy (HREM) has emerged as a very powerful tool for probing the structure of metals and alloys. It has not only helped in unravelling the structure of materials which have been at the forefront of novel materials development such as quasicrystalline phases and high temperature superconducting compounds, but also is fast becoming a technique for solving some outstanding issues in the case of the commercial alloys thereby helping alloy development. In addition to the determination of the structures of phases, this tool is used for obtaining a first hand information of the arrangement of atoms around the various types of crystallographic defects and interphase interfaces. This mode of microscopy allows direct observation of orientation relationships between two phases across interfaces. HREM can be used for the direct examination of the prenucleation process. Initial stages of nucleation can also be studied readily in amorphous alloys, precipitation hardening alloys like maraging steels and in those systems where the formation of the omega phase occurs.
This presentation describes some results of HREM studies on various alloys, commercial as well as alloys of scientific interest, where some of the aforementioned aspects have been examined. The specific examples cited pertain to metallic glasses, NiTi shape memory alloys, Ni-Mo, Zr-Nb and Ti-Al alloys.
Volume 42 | Issue 6
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