Papers by Author: Gautam Kumar Dey

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Authors: Debalay Chakrabarti, S. Roy, Dinesh Srivastava, Gautam Kumar Dey
Abstract: Spatial distribution of microalloy precipitates have been characterized in a low carbon microalloyed steel containing Nb, Ti and V. Micro-segregation during casting resulted in an inhomogeneous distribution of Nb (and also Ti) precipitates in the as-cast slab. Austenite grain growth has been investigated in the above mentioned steel, using different reheating temperatures between 1000°C and 1250°C for 1 h. Inhomogeneous distribution of Nb-rich precipitates created austenite grain size bimodality after reheating to an intermediate temperature range (1150-1200°C). Uniformly fine and uniformly coarse grain structures were found after reheating at lower- (≤ 1075°C) and higher-reheating temperatures (≥ 1250°C). A model has been proposed for the prediction of austenite grain size variation in the reheated steel.
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Authors: Arijit Lodh, Indradev Samajdar, Raghvendra Tewari, Dinesh Srivastava, Gautam Kumar Dey, Prita Pant
Abstract: The present study deals with nanoindentation behavior of commercial Zircaloy 2 and high purity (5N purity) crystal bar Zirconium. The effect of crystal orientation was studied through high resolution electron diffraction, while a finite element model was developed to extract yield strength and strain hardening exponent from nanoindentation data. The study brings in clear signatures of orientation dependence of mechanical properties in hexagonal Zirconium.
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Authors: Karri V. Mani Krishna, Sudipto Mandal, Ankur Agrawal, Vijay Hiwarkar, Dinesh Srivastava, Indradev Samajdar, Gautam Kumar Dey
Abstract: Grain boundary texture evolution in case of two of the Zr based alloys (Zircaloy-4 and Zr-2.5\%Nb) was studied. In case of Zircaloy-4, grain boundary texture evolution during $\beta$ $\to$ $\alpha$ phase transformation was monitored. Direct evidence of variant selection during this transformation is presented. In case of Zr-2.5\%Nb alloy, considerable increase in $\alpha/\beta$ interfaces following Burger's orientation relationship was noticed with increasing annealing time at 700 \textdegree{}C.
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Authors: Santosh Kumar Sahoo, V. D. Hiwarkar, Prita Pant, Indradev Samajdar, Karri V. Mani Krishna, Gautam Kumar Dey, Dinesh Srivastava, R. Tewari, S. Banerjee
Abstract: The present study deals with deformation behaviour of textured Zircaloy 2 with two dominant orientations: basal and non-basal. During initial stages (20%), two distinct class of grains were observed – non-deforming/non-fragmenting grains and deforming/fragmenting grains. The so-called non- deforming/non-fragmenting grains remain equiaxed even after 50% of deformation. They also have insignificant in-grain misorientation developments and have more residual stresses. Dislocation dynamics simulation showed that the dislocation interactions/mobility is insignificant in basal orientations at room temperature deformations.
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Authors: B. Vishwanadh, K.V. Mirji, K. Vaibha, S.K. Jha, R. Ajay Kumar, Indradev Samajdar, Dinesh Srivastava, Gautam Kumar Dey, Raghvendra Tewari
Abstract: The Nb-1%Zr-0.1%C (wt%) alloy is one of the most promising refractory metal alloys having an excellent combination of high temperature properties. Such a combination of properties makes it suitable for several structural applications in the Compact High Temperature Reactor (CHTR). In order to produce the alloy in different shape and sizes a new thermo-mechanical route has been established. The central idea behind the development of such thermo-mechanical route is to reduce the working temperature and provide suitable intermediate annealing treatments to develop desired microstructures. The present paper reports about the application of orientation imaging microscopy in optimizing annealing parameters like temperature and time as a function of the extent of deformation. Samples were also characterized by optical microscopy and transmission electron microscopy techniques. It has been shown that a heat treatment of 1300°C for 3 hour could produce nearly full-recrystallized microstructure. This paper also discusses about the carbide precipitation, their morphologies, chemical compositions and orientations with the matrix phase.
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