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Choudhary B.K.,Indira Gandhi Center for Atomic Research
Materials Science and Engineering A | Year: 2013

Tensile tests were performed on specimens in normalised and tempered condition at temperatures ranging from 300 to 873K and at four strain rates in the range 6.33×10-5 to 6.33×10-3s-1 to examine serrated flow behaviour in 9Cr-1Mo ferritic steel. At all strain rates, the steel exhibited different types of serrations namely type A, B and C serrations at intermediate temperatures, and the nature and type of serrations were strongly dependent on temperature and applied strain rate. Serrations were observed only after a specimen was deformed beyond a critical plastic strain. Critical strain for type A and A+B serrations decreases with increase in temperature and decrease in strain rate. Inverse temperature dependence of critical strain for type C serrations was observed. The activation energy of 86kJmol-1 obtained for serrated flow suggested that diffusion of an interstitial solute such as carbon is responsible for dynamic strain ageing in 9Cr-1Mo steel. © 2012 Elsevier B.V.

Choudhary B.K.,Indira Gandhi Center for Atomic Research
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2014

Tensile tests were performed at strain rates ranging from 3.16 × 10-5 to 3.16 × 10-3 s-1 over the temperatures ranging from 300 K to 1123 K (27 C to 850 C) to examine the effects of temperature and strain rate on tensile deformation and fracture behavior of nitrogen-alloyed low carbon grade type 316L(N) austenitic stainless steel. The variations of flow stress/strength values, work hardening rate, and tensile ductility with respect to temperature exhibited distinct three temperature regimes. The steel exhibited distinct low- and high-temperature serrated flow regimes and anomalous variations in terms of plateaus/peaks in flow stress/strength values and work hardening rate, negative strain rate sensitivity, and ductility minima at intermediate temperatures. The fracture mode remained transgranular. At high temperatures, the dominance of dynamic recovery is reflected in the rapid decrease in flow stress/strength values, work hardening rate, and increase in ductility with the increasing temperature and the decreasing strain rate. © 2013 The Minerals, Metals & Materials Society and ASM International.

Viswanathan R.,Indira Gandhi Center for Atomic Research
Journal of Nuclear Materials | Year: 2014

Clad corrosion being one of the factors limiting the life of a mixed-oxide fast reactor fuel element pin at high burn-up, some aspects known about the key elements (oxygen, cesium, tellurium, iodine) in the clad-attack are discussed and many Fuel-Clad-Chemical-Interaction (FCCI) models available in the literature are also discussed. Based on its relatively superior predictive ability, the HEDL (Hanford Engineering Development Laboratory) relation is recommended: d/μm = ({0.507 × [B/(at.% fission)] × (T/K-705) × [(O/M)i-1.935]} + 20.5) for (O/M)i ≤ 1.98. A new model is proposed for (O/M)i ≥ 1.98: d/μm = [B/(at.% fission)] × (T/K-800)0.5 × [(O/M)i-1.94] × [P/(W cm-1)]0.5. Here, d is the maximum depth of clad attack, B is the burn-up, T is the clad inner surface temperature, (O/M)i is the initial oxygen-to-(uranium + plutonium) ratio, and P is the linear power rating. For fuels with [n(Pu)/n(M = U + Pu)] > 0.25, multiplication factors f are recommended to consider the potential increase in the depth of clad-attack. © 2013 Elsevier B.V. All rights reserved.

Nandi P.K.,Indira Gandhi Center for Atomic Research
Journal of physics. Condensed matter : an Institute of Physics journal | Year: 2010

We calculate properties like equilibrium lattice parameter, bulk modulus and monovacancy formation energy for nickel (Ni), iron (Fe) and chromium (Cr) using Kohn-Sham density functional theory (DFT). We compare the relative performance of local density approximation (LDA) and generalized gradient approximation (GGA) for predicting such physical properties for these metals. We also make a relative study between two different flavors of GGA exchange correlation functional, namely PW91 and PBE. These calculations show that there is a discrepancy between DFT calculations and experimental data. In order to understand this discrepancy in the calculation of vacancy formation energy, we introduce a correction for the surface intrinsic error corresponding to an exchange correlation functional using the scheme implemented by Mattsson et al (2006 Phys. Rev. B 73 195123) and compare the effectiveness of the correction scheme for Al and the 3d transition metals.

Mahendran V.,Indira Gandhi Center for Atomic Research | Philip J.,Indira Gandhi Center for Atomic Research
Applied Physics Letters | Year: 2012

We have developed a simple sensor for imaging internal defects in materials using a magnetically polarizable nanoemulsion. The gradient in the magnetic flux lines around the defective region leads to the formation of one-dimensional nanodroplet arrays along the field direction, which incredibly diffract the incident white light to produce bright colors. As the diffracted wavelength has a direct correlation with the defect features, this approach enable visual inspection of ferromagnetic components and has several advantages over existing flux leakage sensors in terms of cost, re-usability and complexity. © 2012 American Institute of Physics.

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