• BALDEV RAJ

Articles written in Bulletin of Materials Science

• Image analysis system for quantitative metallography

This paper describes a Z-80 microprocessor-based image analyzer developed for global parameter evaluation of images over a 256 × 256 pixel frame. It consists of a microscope,ccd scanner, 6-bit videoadc, Z-80 computer and an image display monitor. Facilities are provided for feature erosion/dilation and halo correction. The paper also presents the details of another more powerful user microprogrammable HP1000 minicomputer-based image analysis system under development. This system consists of an optical microscope/epidiascope coupled to a chalnicon scanner. Here the 512 × 512 pixel image is acquired with 8-bit resolution. It provides for shading correction, auto-delineation, image processing and image analysis functions for evaluation of various basic and derived parameters.

Both the systems are software intensive and are realised according to requirements of quantitative metallography. They can also be used for analysis of images obtained in the fields of biology, medicine, geological survey, photography and space.

• Acoustic emission behaviour during stage II fatigue crack growth in an AISI type 316 austenitic stainless steel

Acoustic emission (AE) behaviour during fatigue crack growth (FCG) in a ductile AISI type 316 austenitic stainless steel is reported. The two substages in the stage II Paris regime of FCG could be distinguished by a change in the rate of acoustic activity with increase in crack growth rate. The transition point in the cumulative ringdown count plot coincides with that in the da/dn plot. The AE activity increases with increase in ΔK during stage IIa and decreases during stage IIb. The major source of AE during stage IIa is found to be the plastic deformation within the cyclic plastic zone (CPZ) as compared to the phenomena such as monotonic plastic zone (MPZ) expansion, ductile crack growth, crack closure, etc. The increase in AE activity with increase in ΔK during stage IIa is attributed to the increase in the size of the CPZ which is generated and developed only under plane strain conditions. The decrease in AE activity during stage IIb is attributed to the decrease in the size of the CPZ under plane stress condition. The high acoustic activity during the substage IIa is attributed to irreversible cyclic plasticity with extensive multiplication and rearrangement of dislocations taking place within the CPZ. The AE activity is found to strongly depend on the optimum combination of the volume of the CPZ, average plastic strain range and the number of cycles before each crack extension. Based on this, an empirical relationship between the cumulative RDC and ΔK has been proposed and is found to agree well with experimentally observed values.

• 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.

• Confocal laser scanning microscopy: Applications in material science and technology

Confocal laser scanning microscope (CLSM) has great advantage over a conventional microscope because it rejects the light that does not come from the focal plane, enabling one to perform optical slicing and construction of three-dimensional (3D) images. Further its high axial resolution, sharp image quality and associated quantitative image analysis provide vital structural information in the mesoscopic range for the full 3D realization of the microstructure. Because of this unique feature, CLSM is now finding wider applications in the study of variety of materials and processes such as phase separation in binary polymer mixtures, fracture toughness in alloys, in determining residual strains in fibre-reinforced metal composites, and in microvisualization of corrosion. This paper reviews some of these recent applications and also discusses our results on colloidal dispersions. CLSM has been used to characterize the amorphous structure in highly-charged colloidal systems which have undergone gas-solid transition. CLSM images show presence of large voids deep inside the disordered suspensions. Frame averaged images reveal that the structural disorder is amorphous. The reasons for voids coexisting with dense amorphous regions and their implications on colloidal interactions are discussed. The article also reviews the use of fluorescence-CLSM in the investigation of novel materials of technological importance such as template-directed colloidal crystals with preferred orientations and multilayered structures with different crystal plane symmetries. Direct measurement of the interfacial curvatures for a bicontinuous polymer blend system as well as real space measurement of structure in phase separating polymer mixtures are now possible using CLSM. This paper reviews some of these results highlighting the unique advantages of confocal microscopy for better understanding of the microstructure and mechanistic aspects of various important phenomena in a large variety of materials.

• Thermogravimetry-evolved gas analysis–mass spectrometry system for materials research

Thermal analysis is a widely used analytical technique for materials research. However, thermal analysis with simultaneous evolved gas analysis describes the thermal event more precisely and completely. Among various gas analytical techniques, mass spectrometry has many advantages. Hence, an ultra high vacuum (UHV) compatible mass spectrometry based evolved gas analysis (EGA–MS) system has been developed. This system consists of a measurement chamber housing a mass spectrometer, spinning rotor gauge and vacuum gauges coupled to a high vacuum, high temperature reaction chamber. A commercial thermogravimetric analyser (TGA: TG + DTA) is interfaced to it. Additional mass flow based gas/vapour delivery system and calibration gas inlets have been added to make it a versatile TGA–EGA–MS facility. This system which gives complete information on weight change, heat change, nature and content of evolved gases is being used for

temperature programmed decomposition (TPD),

synthesis of nanocrystalline materials,

gas–solid interactions and

analysis of gas mixtures.

The TPD of various inorganic oxyanion solids are studied and reaction intermediates/products are analysed off-line. The dynamic operating conditions are found to yield nanocrystalline products in many cases. This paper essentially describes design features involved in coupling the existing EGA–MS system to TGA, associated fluid handling systems, the system calibration procedures and results on temperature programmed decomposition. In addition, synthesis of a few nanocrystalline oxides by vacuum thermal decomposition, gas analysis and potential use of this facility as controlled atmosphere exposure facility for studying gas–solid interactions are also described.

• Materials science research for sodium cooled fast reactors

The paper gives an insight into basic as well as applied research being carried out at the Indira Gandhi Centre for Atomic Research for the development of advanced materials for sodium cooled fast reactors towards extending the life of reactors to nearly 100 years and the burnup of fuel to 2,00,000 MWd/t with an objective of providing fast reactor electricity at an affordable and competitive price.

• Ultrasonic-assisted fabrication of superhydrophobic ZnO nanowall films

Zinc oxide-based superhydrophobic surfaces were fabricated on aluminium oxide-seeded glass substrates via sonochemical approach by varying the parameter, the sonication time duration. The fabricated structures have nanowall-like morphology with an average long axis length and thickness of $\sim$300 and $\sim$40 nm, respectively. The surface roughness createdby surface-modified ZnO nanowalls and the air pockets trapped within the dense nanowalls, transformed the hydrophobic glass substrates into superhydrophobic surfaces with water contact angle of 156$^{\circ}$ during 20 min of sonication. An independent analysis was carried out to study the growth of ZnO nanowalls over glass substrates in the absence of the aluminium oxide seed layer and sonication process. The results suggested that the synergistic effect of the aluminium oxide seed layer and sonochemical process can enable the formation of ZnO nanowall structures favourable for superhydrophobic property. A possible growth mechanism of ZnO nanowalls formation during sonication process has been discussed in detail.

• Materials in harnessing solar power

Harnessing renewable solar energy through different technologies is greatly dependent on the advancement of solar grade materials’ science and engineering. In this article, the prominent solar energy technologies, namely solarphotovoltaic and concentrated solar power and other relevant technologies, and aspects related to various solar grade materials, influence of nanomaterials on enhancement of solar energy harvest, technology–market relations, development of hybrid systems etc., are discussed. The inspiration to write this article is not only to review the existing technologies to harvest solar energy but also to highlight the pertinent and possible solutions thereof, especially from materials perspective.

• # Bulletin of Materials Science

Current Issue
Volume 42 | Issue 6
December 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019