Bhagwati Prasad Kashyap

Abstract: Tensile specimens of Type 316L stainless steel having grain sizes in the range 3.1–86.7 μm were deformed to 34% strain at temperatures 24, 400 and 700°C and strain rate 1 × 10−4s−1 to investigate the Hall-Petch (H-P) relationship, the nature of stress-strain curves and the substructure development. Upto ∼5% strain the H-P relationship exhibits bi-linearity whereas the single Hall-Petch relation is exhibited at larger strains. The presence of bi-linearity is explained by the back stress associated with the difference in the dislocation densities in the vicinity of grain boundary and in the grain interior. The log stress (σ)-log strain (e) plots depict three regimes and follow the relationship σ = Ken in each regime, but with varying magnitudes of the strength coefficient (K) and strain-hardening exponent (n).

Abstract: Forming and forging processes are among the oldest and most important materials related technologies. New materials technologies centre on the development and widespread use of thermomechan...

Abstract: The microstructural aspects of the superplastic phenomenon are reviewed. The experimental results of a very large number of investigations are critically analysed in the context of: grain shape and size; grain growth; grain boundary sliding and migration, grain rotation and rearrangement; diffusion and dislocation activity. It is shown, that in spite of often conflicting evidence in the literature, a common pattern of microstructural behaviour emerges for all the materials and conditions investigated to date.

Abstract: Hydrogen in excess of the terminal solid solubility precipitates out as a brittle hydride phase in zirconium alloys. The hydrides acquire platelet shaped morphology due to their accommodation in the matrix and can cause severe embrittlement, especially when these are oriented normal to the tensile stress axis. The precipitation of hydride platelets normal to the tensile stress when cooled under stress from a solution-annealing temperature is commonly referred to as ‘stress-reorientation’. The stress-reorientation is associated with a threshold stress below which no reorientation is observed. In this work, stress-reorientation of hydrides was investigated for unirradiated, cold worked and stress-relieved Zr–2.5 wt% Nb pressure tube material for a reorientation temperature of 423–723 K. The effect of the reoriented hydrides on the tensile properties of the Zr–2.5 wt% Nb pressure tube alloy was evaluated in the temperature range of 298–573 K.

Abstract: Tensile specimens of type 316L stainless steel with a grain size of 5.0 μm have been deformed at a constant strain rate of 10−3 s−1 over the temperature range 21–900°C and by differential strain-rate test technique over strain rates from about 10−5 to 10−3 s−1 at temperatures in the range 750–900°C. The normalized yield and flow stresses against temperature plots exhibit three regions. While in regions I and III the stresses decrease with increasing temperature, they increase with increasing temperature in region II. Transmission electron microscopy studies on deformed specimens show that at small strains the dislocations generated at grain boundaries have characteristic distributions: in region I the dislocations are confined to the vicinity of the grain boundary, in region II the dislocations are spread into the grain interior, and in region III the dislocations rearrange to form walls. The evolution of substructure and the work-hardening behaviour are explained by considering both intragranula...

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Abstract: A balanced mechanics-materials approach and coverage of the latest developments in biomaterials and electronic materials, the new edition of this popular text is the most thorough and modern book available for upper-level undergraduate courses on the mechanical behavior of materials To ensure that the student gains a thorough understanding the authors present the fundamental mechanisms that operate at micro- and nano-meter level across a wide-range of materials, in a way that is mathematically simple and requires no extensive knowledge of materials This integrated approach provides a conceptual presentation that shows how the microstructure of a material controls its mechanical behavior, and this is reinforced through extensive use of micrographs and illustrations New worked examples and exercises help the student test their understanding Further resources for this title, including lecture slides of select illustrations and solutions for exercises, are available online at wwwcambridgeorg/97800521866758

Abstract: Most natural (or biological) materials are complex composites whose mechanical properties are often outstanding, considering the weak constituents from which they are assembled. These complex structures, which have risen from hundreds of million years of evolution, are inspiring Materials Scientists in the design of novel materials. Their defining characteristics, hierarchy, multifunctionality, and self-healing capability, are illustrated. Self-organization is also a fundamental feature of many biological materials and the manner by which the structures are assembled from the molecular level up. The basic building blocks are described, starting with the 20 amino acids and proceeding to polypeptides, polysaccharides, and polypeptides–saccharides. These, on their turn, compose the basic proteins, which are the primary constituents of ‘soft tissues’ and are also present in most biominerals. There are over 1000 proteins, and we describe only the principal ones, with emphasis on collagen, chitin, keratin, and elastin. The ‘hard’ phases are primarily strengthened by minerals, which nucleate and grow in a biomediated environment that determines the size, shape and distribution of individual crystals. The most important mineral phases are discussed: hydroxyapatite, silica, and aragonite. Using the classification of Wegst and Ashby, the principal mechanical characteristics and structures of biological ceramics, polymer composites, elastomers, and cellular materials are presented. Selected systems in each class are described with emphasis on the relationship between their structure and mechanical response. A fifth class is added to this: functional biological materials, which have a structure developed for a specific function: adhesion, optical properties, etc. An outgrowth of this effort is the search for bioinspired materials and structures. Traditional approaches focus on design methodologies of biological materials using conventional synthetic materials. The new frontiers reside in the synthesis of bioinspired materials through processes that are characteristic of biological systems; these involve nanoscale self-assembly of the components and the development of hierarchical structures. Although this approach is still in its infancy, it will eventually lead to a plethora of new materials systems as we elucidate the fundamental mechanisms of growth and the structure of biological systems.

Abstract: This article presents an overview of the developments in stainless steels made since the 1990s. Some of the new applications that involve the use of stainless steel are also introduced. A brief introduction to the various classes of stainless steels, their precipitate phases and the status quo of their production around the globe is given first. The advances in a variety of subject areas that have been made recently will then be presented. These recent advances include (1) new findings on the various precipitate phases (the new J phase, new orientation relationships, new phase diagram for the Fe–Cr system, etc.); (2) new suggestions for the prevention/mitigation of the different problems and new methods for their detection/measurement and (3) new techniques for surface/bulk property enhancement (such as laser shot peening, grain boundary engineering and grain refinement). Recent developments in topics like phase prediction, stacking fault energy, superplasticity, metadynamic recrystallisation and the calculation of mechanical properties are introduced, too. In the end of this article, several new applications that involve the use of stainless steels are presented. Some of these are the use of austenitic stainless steels for signature authentication (magnetic recording), the utilisation of the cryogenic magnetic transition of the sigma phase for hot spot detection (the Sigmaplugs), the new Pt-enhanced radiopaque stainless steel (PERSS) coronary stents and stainless steel stents that may be used for magnetic drug targeting. Besides recent developments in conventional stainless steels, those in the high-nitrogen, low-Ni (or Ni-free) varieties are also introduced. These recent developments include new methods for attaining very high nitrogen contents, new guidelines for alloy design, the merits/demerits associated with high nitrogen contents, etc.

Abstract: Many traditional approaches for strengthening steels typically come at the expense of useful ductility, a dilemma known as strength-ductility trade-off. New metallurgical processing might offer the possibility of overcoming this. Here we report that austenitic 316L stainless steels additively manufactured via a laser powder-bed-fusion technique exhibit a combination of yield strength and tensile ductility that surpasses that of conventional 316L steels. High strength is attributed to solidification-enabled cellular structures, low-angle grain boundaries, and dislocations formed during manufacturing, while high uniform elongation correlates to a steady and progressive work-hardening mechanism regulated by a hierarchically heterogeneous microstructure, with length scales spanning nearly six orders of magnitude. In addition, solute segregation along cellular walls and low-angle grain boundaries can enhance dislocation pinning and promote twinning. This work demonstrates the potential of additive manufacturing to create alloys with unique microstructures and high performance for structural applications.