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Singh G.,Indian Institute of Science | Gaddam R.,Lulea University of Technology | Petley V.,Gas Turbine Research Establishment | Datta R.,International Center for Materials Science | And 4 more authors.
Scripta Materialia | Year: 2013

The strain-controlled fatigue behaviour of Ti-6Al-4V alloy with up to 0.11 wt.% B addition was investigated. Results show significant softening when the strain amplitudes, ΔεT/2, are ≥0.75%. B addition was found to improve the fatigue life for ΔεT/2 ≤ 0.75% as it corresponds to the elastic regime and hence is strength dominated. At ΔεT/2 = 1%, in contrast, the base alloy exhibits higher fatigue life as TiB particle cracking due to strain incompatibility causes easy crack nucleation in the B-modified alloys. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Singh G.,Indian Institute of Science | Satyanarayana D.V.V.,Indian Defence Research And Development Laboratory | Pederson R.,GKN plc | Pederson R.,Lulea University of Technology | And 3 more authors.
Materials Science and Engineering A | Year: 2014

The addition of B, up to about 0.1. wt%, to Ti-6Al-4V (Ti64) reduces its as-cast grain and colony sizes by an order of magnitude. In this paper, the creep resistance of this alloy modified with 0.06 and 0.11. wt% B additions was investigated in the temperature range of 475-550. °C and compared with that of the base alloy. Conventional dead-weight creep tests as well as stress relaxation tests were employed for this purpose. Experimental results show that the B addition enhances both elevated temperature strength and creep properties of Ti64, especially at the lower end of the temperatures investigated. The steady state creep rate in the alloy with 0.11. wt% B was found to be an order of magnitude lower than that in the base alloy, and both the strain at failure as well as the time for rupture increases with the B content. These marked improvements in the creep resistance due to B addition to Ti64 were attributed primarily to the increased number of inter-phase interfaces - a direct consequence of the microstructural refinement that occurs with the B addition - that provide resistance to dislocation motion. © 2014 Elsevier B.V.

Rao C.N.R.,International Center for Materials Science
Journal of Physical Chemistry Letters | Year: 2015

Although it is customary to substitute cations in metal oxides, sulfides, and other materials to modify their structure and properties, effects of anion substitution have not been investigated sufficiently. This is particularly true of materials cosubstituted by two anions (such as N3- and F- in place of O2- or P3- and Cl- in place of S2-). Substitution of a trivalent anion along with a monovalent anion helps to eliminate defects, the three anions being isoelectronic and of nearly the same size. Furthermore, such aliovalent anion substitution gives rise to marked changes in the electronic structure and properties. Isovalent anion substitution (e.g., S2- in place of O2- or Se2- in place of S2-) does not bring about such changes. In this Perspective, we examine the electronic structures and properties of several oxides involving cosubstitution of N and F for oxygen. The oxides discussed are TiO2, ZnO, Cr2O3, and BaTiO3. Aliovalent anion substitution decreases the band gaps of the oxides and affect the magnetic and ferroelectric transitions. Sulfides such as CdS and ZnS where sulfur is substituted by P and Cl also show a large decrease in band gaps. Unlike in cation substitution where the conduction band is mainly affected, in the aliovalent anion-substituted materials the p-states of the trivalent anions (N3- and P3-) dominate the top of the valence band, with the metal-trivalent anion (N, P) bond being shorter and the metal-halogen bond longer. Such materials with high visible absorption extending to long wavelengths may indeed find uses. © 2015 American Chemical Society.

Datta K.K.R.,Jawaharlal Nehru Centre for Advanced Scientific Research | Jagadeesan D.,Jawaharlal Nehru Centre for Advanced Scientific Research | Jagadeesan D.,University of Toronto | Kulkarni C.,Jawaharlal Nehru Centre for Advanced Scientific Research | And 4 more authors.
Angewandte Chemie - International Edition | Year: 2011

A structural chameleon: A porous layered carbon material (PLC) containing nanographene domains was prepared by graphitizing glucose within the nanoscopic voids of an aminoclay template. The size of the pores in the PLC was altered reversibly by a mesoscale order-disorder transformation brought about by an applied mechanical force (see picture). This pore flexibility was exploited for the size-selective separation of dye molecules. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Devidas T.R.,Indira Gandhi Center for Atomic Research | Chandra Shekar N.V.,Indira Gandhi Center for Atomic Research | Sundar C.S.,Indira Gandhi Center for Atomic Research | Chithaiah P.,International Center for Materials Science | And 7 more authors.
Journal of Physics Condensed Matter | Year: 2014

Noting that BiI3 and the well-known topological insulator (TI) Bi2Se3 have the same high symmetry parent structures, and that it is desirable to find a wide-band gap TI, we determine here the effects of pressure on the structure, phonons and electronic properties of rhombohedral BiI3. We report a pressure-induced insulator-metal transition near 1.5 GPa, using high pressure electrical resistivity and Raman measurements. X-ray diffraction studies, as a function of pressure, reveal a structural peculiarity of the BiI3 crystal, with a drastic drop in c/a ratio at 1.5 GPa, and a structural phase transition from rhombohedral to monoclinic structure at 8.8 GPa. Interestingly, the metallic phase, at relatively low pressures, exhibits minimal resistivity at low temperatures, similar to that in Bi2Se3. We corroborate these findings with first-principles calculations and suggest that the drop in the resistivity of BiI3 in the 1-3 GPa range of pressure arises possibly from the appearance of an intermediate crystal phase with a lower band-gap and hexagonal crystal structure. Calculated Born effective charges reveal the presence of metallic states in the structural vicinity of rhombohedral BiI3. Changes in the topology of the electronic bands of BiI3 with pressure, and a sharp decrease in the c/a ratio below 2 GPa, are shown to give rise to changes in the slope of phonon frequencies near that pressure. © 2014 IOP Publishing Ltd.

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