• Volume 19, Issue 6

December 1996,   pages  837-1165

• Foreword

• A perspective on materials characterization for technology advancement and industrial growth: Emphasis on non-destructive evaluation

Materials are the index of human progress. The evolution of mankind is linked to materials, for example, stone age, bronze age, iron age etc. The success of use of materials towards better quality of human life depends on the capabilities for characterization of these materials, which leads to ensuring reliable performance of the materials and development of new, and more efficient materials. The materials characterization encompasses determining chemical constituents, microstructural characterization down to a few Angstroms level and defect assessment from a few micrometers to few millimeters in a wide variety of materials. Recent progress made in the nondestructive characterization of materials and the future trends and direction are discussed in this paper.

• Sixty years of dislocations

It is well-known that with the appearance of three independent papers by Taylor, Polanyi and Orowan in the year 1934, the concept of crystal dislocations was born. Since then, dislocation theory has had many spectacular successes. It is quite appropriate therefore to be aware of the state of development of this exciting subject, sixty years after its discovery.

A flavour for the vast subject of the applications of dislocation mechanisms to real materials is presented by choosing three examples, one each, drawn from metallurgy, physics and electronics. The topic of ‘Strength of metals and alloys’ is the first one, as this is also the author’s area of research. The phenomenon of solidification and crystal growth forms the next topic, especially in view of the seminal contributions made by A R Verma and his school from India. Dislocations play a useful role in the strengthening of solids, but how influential are they in affecting the performance of modern semiconductor devices? In the third example, the interesting and painstaking work done to settle this question is reviewed.

Can we regard carbon fibre as thetransistor of dislocation theory? How shall we understand the long-established effects such as corrosion-fatigue, superplasticity and shape memory as well as the electrochemical and electro-mechanical properties of dislocations in semiconductor and non-metallic crystals? Answers to these questions belong to the realms of the future developments in dislocations. The talk is concluded with a discussion of these topics.

• New materials for the twenty-first century and the role of Tata Steel

• From product-oriented to process-oriented: Emerging new engineering paradigm

The conventional approach has put emphasis upon reducing labour, and increasing efficiency and uniformity. But this holds good only in the mass production paradigm. As we are entering the age of small production with far wider varieties, these principles of yesterday should be re-examined. Labour itself sometimes gives satisfaction if it involves the joy of creation, and longer time does not necessarily mean just patience, it sometimes turns into expectation if greater joy will be provided later. Too much fitness for the purpose sometimes means lack of robustness and adaptability to the quickly and widely changing environment. Thus, we should reconsider the items we thought important in the mass production age to aptly cope with the diversification of each customer’s requirements.

• Production of low phosphorus steels from high phosphorus Indian hot metal: Experience at Tata Steel

The position in India on the phosphorus front vis-a-vis iron and steel operations elsewhere in the world is, and will remain, most unfavourable since Indian iron ores contain high phosphorus and coal (and therefore, also the coke), has high ash and phosphorus in the Indian subcontinent. While dephosphorization of hot metal is theoretically ruled out in the Indian context, dephosphorization of liquid steel can also not be considered because of its adverse effect on ladle refractories and steel cleanliness.

For a large proportion of the steels made through the LD-slab caster-hot strip mill route at Tata Steel, the phosphorus content required in the product is 0·020% max and in some grades, it is restricted to 0·015% max. Various control strategies evolved to make low phosphorus steel at Tata Steel are discussed in the paper. The major steps which have significantly reduced the phosphorus levels are described.

• Recent trends in alumina and aluminium production technology

For well over a century the Bayer process for the production of alumina from bauxite and the Hall-Heroult process involving the electrolysis of alumina dissolved in cryolite to produce aluminium have been commercially exploited. However, significant advances based on intense research and development activities in the last five decades have led to considerable improvements in operating parameters and productivity, efficient disposal and utilization of wastes. This review presents the developments that have taken place in technology, equipment and treatment of wastes in both the alumina and aluminium production processes.

Technology and equipment developments in the field of alumina are concerned with usage of different qualities of bauxite, improvement in extraction efficiency of alumina from bauxite, obtaining better yield during precipitation, enhancing scale of operation and minimizing soda losses in the process. Improvements in electrolysis involve utilization of modified electrolytic baths, controlled feeding of alumina, better design of cell based on mathematical modelling of magnetic field and heat distribution and optimization of the performance of electrodes on the basis of good understanding of physical, mechanical and electrical properties. Information on the present situation in the Indian plants is also presented. Proper treatment and disposal of wastes generated in alumina and aluminium production are of great importance as they contain significant amounts of sodium hydroxide, fluorides, sulphur dioxide, oxides of carbon and cyanide. Some attempts made to utilize the waste material are briefly summarized.

• Development of technologies for large scale production of titanium and magnesium metals at the defence metallurgical research laboratory, Hyderabad

Titanium has been finding increasing usage as a structural metal in aerospace and many non-aerospace sectors mainly due to its light weight, high strength and outstanding corrosion resistance properties. India is very fortunate to possess the world’s largest and richest mineral deposit for this metal. Early studies on the metal extraction during mid ’60s at the Bhabha Atomic Research Centre, Bombay and pilot plant studies at the Nuclear Fuel Complex, Hyderabad resulted in the establishment of a ‘Technology Development Centre’ at Defence Metallurgical Research Laboratory (DMRL), Hyderabad. DMRL has already demonstrated titanium sponge production feasibility in 2,000 kg batches by the conventional Krcll process and is presently engaged in the development of the more energy saving ‘combined process technology’ in 4,000 kg batches. Fused salt electrolysis is widely employed to produce magnesium metal in integrated titanium plants so as to regenerate magnesium from the by-product magnesium chloride. DMRL has developed magnesium electrolysis technology in a 30 kA monopolar, modular type cell and is now developing the multipolar cell technology in 7kA, 22·2 V, two-module cell equipped with five bipoles in each module. This paper traces the developmental efforts on titanium metal extraction in India and describes the current efforts underway at DMRL for developing the latest energy efficient and cost effective technologies for the large scale production of both titanium and magnesium metals.

• Synthesis of nanocrystalline alloys and intermetallics by mechanical alloying

Nanocrystalline Al3Ni, NiAl and Ni3Al phases in Ni-Al system and theα, β, γ, ɛ and deformation induced martensite in Cu-Zn system have been synthesized by mechanical alloying (MA) of elemental blends in a planetary mill. Al3Ni and NiAl were always ordered, while Ni3Al was disordered in the milled condition. MA results in large extension of the NiAl and Ni3Al phase fields, particularly towards Al-rich compositions. Al3Ni, a line compound under equilibrium conditions, could be synthesized at nonstoichiometric compositions as well by MA. The phases obtained after prolonged milling (30 h) appear to be insensitive to the starting material for any given composition &gt; 25 at.% Ni. The crystallite size was finest (∼ 6 nm) when NiAl and Ni3Al phases coexisted after prolonged milling. In contrast, in all Cu-Zn blends containing 15 to 85 at.% Zn, the Zn-rich phases were first to form, and the final crystallite sizes were coarser (15–80 nm). Two different modes of alloying have been identified. In case of NiAl and Al3Ni, where the ball milled product is ordered, as well as, the heat of formation (ΔHf) is large (&gt; 120 kJ/mol), a rapid discontinuous mode of alloying accompanied with an additive increase in crystallite size is detected. In all other cases, irrespective of the magnitude of ΔHf, a gradual diffusive mode of intermixing during milling seems to be the underlying mechanism of alloying.

• Chemical synthesis of nanosized oxides

Fine powder of single and binary mixed oxides can be produced by decomposition of the respective metal nitrates and polyvinyl alcohol (PVA) or, a mixture of PVA and polyacrylic acids. These mixtures, after spray drying, yield a brown fluffy mass, which is spontaneously combustible and the heat liberated is sufficient for the crystallization of the desired oxide phase. The rate of combustion controls the growth of the particles. This can be manifested by combustion of the mixture in controlled atmosphere. The nanoparticles of the oxide system studied are: spinels [MFe2O4 where M = Ni(II), Co(II), Zn(II), Mg(II)]; orthoferrites [MFeO3 where M = Gd(III), Sm(III)]; LaAlO3, NdGaO3, CaO/MgO/Y2O3 stabilized zirconia (ZrO2); lead zirconate titanate (PZT), lanthanum modified lead zirconate titanate (PLZT) and BaTiO3.

• On the formability of sheet steels

Formability of sheet steel in stamping operation primarily depends on strain hardening exponent (n), average plastic strain ratio ($$\bar r$$) and the maximum strain the material can undergo before the onset of localized necking. The formability parameters (n and$$\bar r$$) and the forming limit diagrams have been evaluated for a variety of sheet steel products, extensively used for press forming of components of diverse shapes e.g. extra deep drawing quality auto-body sheets, high strength cold rolled sheets, LPG steel for gas cylinders, austenitic and ferritic stainless steels, etc. The effect of sulphide shape control on formability of hot rolled HSLA steel has also been studied. Additionally, the press performance of auto-body sheets and austenitic stainless steels have been monitored and evaluated at customer’s end for complete information on the formability.

• Creep of austenitic stainless steel welds

Austenitic stainless steels (SS) find extensive application in power, petrochemical and nuclear industries in view of their excellent elevated temperature mechanical properties, corrosion resistance, formability and weldability. However, they are susceptible to hot cracking during fusion welding. To avoid this problem, chemical composition of the welding consumable is generally adjusted to promote primary ferrite mode of solidification and retain about 3 to 10%δ-ferrite in the as-welded condition. The duplex microstructure of the weld metal undergoes transformation to carbides and a variety of intermetallic phases during elevated temperature service and causes deterioration in the mechanical properties.

This paper presents a comprehensive review of the current understanding of the solidification microstructures, ageing processes and their influence on the creep behaviour of types 308 and 316 SS weld metals. The effects of varying chemical composition,δ-ferrite content, electrode coating and welding processes on creep strength and ductility are examined. Current trends in the design of welded components for creep application are also discussed.

• Effect of gamma prime depletion on creep behaviour of a nickel base superalloy (Inconel alloy X-750)

Specimens of a nickel base superalloy were exposed to air at 1423 K to study the effect of gamma prime depletion in the near-surface region on the creep behaviour of the alloy. The results showed that the gamma prime depletion in the air-exposed specimens caused a weakening effect, leading to enhanced creep rate. Kachanov’s damage parameterf was determined and was found to be 0·5 indicating that the near-surface region, comprising of surface oxide, grain boundary oxide and gamma prime depleted region, carried a small fraction of the applied stress. It is further shown that the damaging effect is more pronounced in thinner specimens.

• Emerging uses of aluminium in late 20th and early 21st century

Aluminium a metal of this century will emerge as the most versatile metal with wide application in transport, building and packaging sectors. Aluminium is only next to Iron and Steel in its availability and wide range of electro-mechanical properties. It combines the strength and toughness of steel alongwith electrical conductivity of copper. In the area of energy efficient and light weight designs, aluminium and its alloys will score over all other materials. The paper highlights the trend of application and their growth in the early part of the next century.

• Missile materials—Current status and challenges

Missile Development Programme has provided focal thrust to indigenous materials and components. Materials have been selected on the basis of their high strength to weight ratio, good corrosion resistance, high fracture toughness, easy fabricability and reliable quality. Alloys of magnesium, aluminium, titanium and maraging steel are extensively used for airframe and propulsion systems. Polymer materials and carbon-carbon composites are major nonmetallic materials. Development of high purity electronic materials like silicon, indium, phosphorus, Cu clad materials, photo resists and epoxies are very important for the programme. The paper covers the requirements and challenge areas of research, and calls for consortium approach involving academic institutions. R and D laboratories and industries to ensure self reliance.

• Superconducting materials and applications

The field of superconductivity has witnessed tremendous excitement in recent years, starting with the discovery of what has come to be known as ‘high temperature superconductors’. This has led to extensive activity on many aspects concerning the mechanism of superconductivity, new materials and systems and their technological applications. Further impetus to research in this area has been provided by the discovery of superconductivity in doped fullerenes. The first identification of superconductivity in a quarternary borocarbide system Y-Ni-B-C which must be regarded as the foremost fundamental Indian contribution in recent times, has further stimulated interest in this field. Notwithstanding the new excitements, the conventional superconductors continue to be the workhorses for technological applications. This review selectively presents some of the aspects of the developments in the entire gamut of the known superconducting systems from the stand point of materials and their applications.

• Microclusters as superatoms for developing new materials

With the discovery of solid C60, efforts are being made to develop new clusters and molecules which could be assembled to form new materials. Here we present some recent developments in this direction and discuss bonding in such materials.

• Characterization of La1 −xSr1 +xCu5 −xFex O12 + δ (0 ≤x ≤ 1·0) by dc electrical conductivity, magnetic susceptibility and EPR measurements(0 ≤x ≤ 1·0) by dc electrical conductivity, magnetic susceptibility and EPR measurements

The DC electrical resistivity results of La4 −xSr1 +xCu5 −xFex O12 + δ (0 ≤x ≤ 1·0) showed that for S1 (x = 0) and S2 (x = 0·25) the temperature coefficient of resistivity (TCR), dρ/dT, is positive and slightly increases with increasing temperature in the range 20–270 K. This shows the metallic nature of S1 and S2. For the samples S3(x = 0·5) and S4 (x = 0·75), TCR slightly increases in the range 20–270 K, with change in sign from negative to positive at ∼ 80 K and ∼ 130 K, respectively. These results show the metal-insulator type transition in S3 and S4. For the sample S5 (x = 1·0), the TCR is negative and gradually increases in the range 20–270 K, which shows its semiconductor-like behaviour. The activation energy for S5 is found to be 0·21 × 10−2 eV. Furthermore, the DC resistivity results of S1–S5 in the range 350–660 K are in conformity with the low temperature results. The very weak temperature dependence of magnetic susceptibility results of S1–S3 show Pauli-paramagnetic behaviour in the range 77K–400 K, while S4 and S5 exhibit Pauli-paramagnetic behaviour in the range 77–850 K. Long-range antiferromagnetic interaction is observed in S5 (x = 1·0) belowTc ∼ 100 K. The room temperature EPR lineshapes gradually improve from metallic S1 (x = 0) to semiconductor-like S5(x = 1·0). Negativeg-shift is observed in the samples S2–S5 with increasing trend ingiso-values of 1·880 in S2 to 1·961 in S5. However, thegiso-value for S1 could not be observed due to very poor lineshape.

• Electrical conduction in the system Sr0·90La0·10Ti0·90M′0·10O3 (M′ = Co, Ni or Cr)

We have successfully synthesized the system Sr1 −xLaxTi1 −xM′xO3 where M′ = Cr, Ni and Co by using conventional solid state ceramic method. Powder X-ray diffraction patterns of the different compositions show the formation of single phase materials. Measurement of AC conductivity as a function of frequency at different temperatures in the range 300–550 K show that conduction in these compositions occurs due to hopping of charge carriers between localized transition metal ion sites.

Cadmium(II) metavanadate has crystal structure related to brannerite (ThTi2O6) structure. The high temperatureβ-CdV2O6 phase isn-type semiconductor between 185 and 750°C. The electrical conduction in theβ-CdV2O6 occurs due to deviation from oxygen stoichiometric composition of the lattice. The seebeck coefficient (α) of the sample is negative and constant in the entire range of investigation. The mechanism of transport in cadmium metavanadate lattice is via thermally activated hopping of localized electrons on vanadium (V5+) sites of the lattice. The DTA result indicated that CdV2O6 undergoes phase transition at 185°C and not at 670°C as reported earlier. There is no DTA evidence to show the possibility ofβα phase reverse transition. The XRD powder patterns of the two modifications are nearly similar indicating brannerite related structures. The infrared absorption band of vanadium-oxygen stretching vibration modes of distorted VO6 octahedra ofβ-CdV2O6 is exhibited at 855 cm−1.

• Structural and dielectric properties of Pb(Li1/4Sm1/4Mo1/2)O3 ceramics

The ceramic samples of lithium-samarium modified lead molybdate, Pb(Li1/4 Sm1/4 Mo1/2)O3 (PLSM)—a member of ABO3 family were prepared by solid state reaction technique at ≈ 600–700°C. Preliminary X-ray analysis suggests the formation of single phase orthorhombic compound of PLSM. Studies of surface morphology, uniform particle/grain distribution, and presence of elements in the compound were completed using scanning electron microscope (SEM). Measurements of dielectric constant (ɛ), loss (tanδ) and conductivity (σ) at different frequencies and temperatures provided that the compound has a strong dielectric anomaly at 107°C.

• EPMA, EPR, electronic and vibrational spectral studies on natural aurichalcite

The electron probe micro analysis (EPMA), electron paramagnetic resonance (EPR), electronic and vibrational spectral studies on a natural mineral, aurichalcite were studied at room temperature. The EPMA analysis revealed the concentration of copper in the mineral to be 2·6 wt% and zinc as 24·5 wt%. The optical spectra revealed the presence of copper inD4h symmetry with crystal field (Dq) and tetragonal field (Ds andDt) parameters as 1250, 1600 and 520 cm−1 respectively. This further confirmed the presence of Cu(II) ion in an elongated tetragonal site. The EPR studies indicated the presence of Cu(II) ion, but hyperfine lines could not be resolved due to the high concentration of the paramagnetic impurity in the mineral. The IR spectrum confirmed the presence of water and carbonate ion.

• 57Fe Mössbauer studies on natural chromites

Five chromite samples procured from two different belts of India have been studied by57Fe Mössbauer spectroscopy. It is shown that four symmetric doublets are sufficient to fit the chromite spectrum; the Mössbauer parameters and the Fe3+/Fe2+ ratio are computed. For fully oxidized chromite with only Fe3+, two doublets are needed and the parameters are computed.

• Alkali tellurite glasses: Bonding, structure and conductivity

The nature of the Te-O bond and charge transfer between alkali atoms and Te-O polyhedra in alkali-tellurite glasses is discussed in connection with ion transport in these glasses. Experimental results on XPS, neutron and Raman scattering support the empirical picture developed here. The overall kinetics of the interchange transport mechanism for conduction in single and mixed alkali-tellurite glasses is apparently determined by the kinetics of the alkali ion—glass former ion interchange—an aspect to be probed experimentally.

• Electron beam deposition system for X-ray multilayer mirrors

We have developed a multi source electron beam evaporation system toprepare high quality X-ray multilayer mirrors. The system has three electron guns mounted in an ultra high vacuum chamber. The deposition system is evacuated by a turbo molecular pump and two sputter ion pumps. A movable masking system is mounted to deposit several kinds of multilayers. First results on niobium-carbon X-ray multilayers are presented.

• Refinement of directed melt oxidized structures

Composite microstructures obtained via directed melt oxidation can be refined using external reinforcements and alloying additions. The mechanisms responsible for refinement of composite (alumina) microstructure are discussed.

• Fast neutron activation analysis of glycidyl azide polymers

Fast neutron activation analysis technique using 14 MeV neutrons has been applied to analyse nitrogen, chlorine and oxygen content of glycidyl azide polymers (GAP) with$$\bar M$$n around 2100. It has been found that the method is better suited for elemental analysis of GAP than infrared spectroscopy. In fact IR spectral analysis fails to detect chlorine in the polymer when the chlorine content is approximately less than 20%. Oxygen is directly measured by fast neutron activation analysis which is unique.

• Repeated drop weight impacts and post-impact ILSS tests on glass-epoxy composite

E glass epoxy laminates of thicknesses in the range 2–5 mm were subjected to repeated impacts. For each thickness the number of hits to cause tup penetration was determined and the value of this number was higher the larger the thickness of the laminate tested. The C-scan, before and after impact, was done to obtain information regarding flaw distribution. Short beam shear test samples were made from locations at fixed distances from impact point and tested. The samples closer to the zone of impact showed lower strength values. Scanning fractography revealed shear deformation features for these samples and brittle fracture features for the region near the zone of impact.

• Study of fracture features in foam bearing glass epoxy composites subjected to repeated impacts

The paper reports the failure features observed in low mass repeatedly (pendulum) impacted glass epoxy composites with and without the mid section having either 2-layers or 3-layers of flexible foam. Features such as through width and inclined cracks as well as adhering of foam observed in the experiments are explained. The significance of the foam material in modifying the impact response of the composite is stressed.

• Anisotropic studies of quenched and indented potassium bromide cleavages

Kick’s law and modified Kick’s law for pyramidal indenter were used to study the mechanical response of indented and quenched potassium bromide cleavages. The study has disclosed an unusual interpretation of constants in the above laws. It suggested a pair of anisotropic indices which characterize a crystallographic direction. This study has also shown that there is atleast one crystallographic direction usually termed as homogeneous isotropic direction along which their mechanical properties are same. The implications are discussed in detail.

• Rapid microwave assisted synthesis of hydroxyapatite

A fast, efficient and novel method of preparation of hydroxyapatite using microwaves has been described.

• Bulletin of Materials Science

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• Editorial Note on Continuous Article Publication

Posted on July 25, 2019