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Fuloria D.,Indian Institute of Technology Roorkee | Goel S.,Indian Institute of Technology Roorkee | Jayaganthan R.,Indian Institute of Technology Roorkee | Srivastava D.,Bhabha Atomic Research Center | And 2 more authors.
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2015

The mechanical properties and microstructural evolution of zircaloy-4 subjected to cumulative strains of 1.48, 2.96, 4.44 and 5.91 through multiaxial forging (MAF) at cryogenic temperature (77 K) were investigated. The mechanical properties of the MAF treated alloy were measured through universal tensile testing and Vickers hardness testing equipment. The zircaloy-4 deformed up to a cumulative strain of 5.91 showed improvement in both ultimate tensile strength and hardness from 474 MPa to 717 MPa and from HV 190 to HV 238, respectively, as compared with the as-received alloy. However, there was a noticeable decrement in ductility (from 18% to 3.5%) due to the low strain hardening ability of deformed zircaloy-4. The improvement in strength and hardness of the deformed alloy is attributed to the grain size effect and higher dislocation density generated during multiaxial forging. The microstructural evolutions of deformed samples were characterized by optical microscopy and transmission electron microscopy (TEM). The evolved microstructure at a cumulative strain of 5.91 obtained after MAF up to 12 cycles depicted the formation of ultrafine grains with an average size of 150-250 nm. © 2015 The Nonferrous Metals Society of China.


Saxena K.K.,Indian Institute of Technology Roorkee | Sonkar S.,Indian Institute of Technology Roorkee | Pancholi V.,Indian Institute of Technology Roorkee | Chaudhari G.P.,Indian Institute of Technology Roorkee | And 4 more authors.
Journal of Alloys and Compounds | Year: 2016

Dynamic materials model (DMM), modified dynamic materials model (MDMM) and α-parameter were used to develop processing maps of Zr-2.5Nb alloy. Gleeble-3800® thermo-mechanical simulator was used to obtain flow stress at different temperatures and strain rates in the range of 700-925 °C and 0.01-10 s-1 respectively. Suitability of the three models in predicting the hot deformation behavior of Zr-2.5Nb alloy was evaluated by microstructural studies. DMM was found appropriate to delineate different deformation conditions for this alloy. © 2015 Elsevier B.V. All rights reserved.


Goel S.,Indian Institute of Technology Roorkee | Jayaganthan R.,Indian Institute of Technology Roorkee | Singh I.V.,Indian Institute of Technology Roorkee | Srivastava D.,Bhabha Atomic Research Center | And 2 more authors.
Acta Metallurgica Sinica (English Letters) | Year: 2015

The texture and mechanical properties of cross-rolled zircaloy-2 at 77 and 300 K were investigated. Crossrolling at 77 K was performed to impart different thickness reductions of 25% and 50%, while at 300 K with 25%, 50%, 75% and 85% reductions to the sample. EBSD analysis of deformed sample showed that near-basal orientation is not deformed completely after 50% rolling reduction. The activation of prismatic silp, {1122} contraction twin and {1012} extension twin were evident from the deformed microstructure at 77 K. The propensity for activation of basal slip\a[at 77 K was also observed. The deformation of the sample at 300 K occurs by prismatic, basal\a[and pyramidal\c a[ slips, which were predicted by pole figures. After annealing, the tensile strengths (735 and 710 MPa) are almost the same for 50% cryo-cross-rolled and room-temperature cross-rolled zircaloy-2 with almost 2.7% difference in their ductility. KAM analysis of the deformed samples was made to estimate the stored strain energy and dislocation density. Annealing of deformed sample at 673 K for 30 min results in recrystallization, which leads to the formation of ultrafine grains.


Fuloria D.,Indian Institute of Technology Roorkee | Kumar N.,Indian Institute of Technology Roorkee | Goel S.,Indian Institute of Technology Roorkee | Jayaganthan R.,Indian Institute of Technology Roorkee | And 3 more authors.
Materials and Design | Year: 2016

The effect of rolling at different temperatures and deformation strains on the variation in hardness and tensile properties of Zircaloy-4 has been investigated in the present work. The initial hot extruded and annealed Zircaloy-4 was subjected to various rolling reductions of 25%, 50%, 70%, and 90% at room (298 K) and liquid nitrogen (77 K) temperatures along extrusion and transverse directions of the as-received bar, respectively. The hardness and ultimate tensile strength (UTS) obtained for samples rolled to a true strain of 2.3 along the extrusion direction were 264.67 ± 3.8 HV, 786 MPa at 298 K, and 273.57 ± 1.6 HV, 856 MPa at 77 K, while along the transverse direction, the hardness and UTS values observed were 262.7 ± 3.77 HV, 727 MPa at 298 K, and 266.57 ± 2.7 HV, 827.63 MPa at 77 K. The enhancement in strength and hardness of the Zr alloy is attributed to increase in the stacking fault probability (SFP) with the applied progressive true strains at different temperatures, which led to the greater accumulation of dislocation density and hence a better grain refinement. © 2016 Elsevier Ltd.


Saxena K.K.,Indian Institute of Technology Roorkee | Pancholi V.,Indian Institute of Technology Roorkee | Srivastava D.,Bhabha Atomic Research Center | Dey G.K.,Bhabha Atomic Research Center | And 2 more authors.
Materials Science Forum | Year: 2015

Hot workability of Zr-2.5Nb-0.5Cu alloy has been investigated by means of hot compression test using Gleeble-3800®, in the temperature and strain rate range of 700 to 925°C and 0.01 -10s-1, respectively. Deformation behavior was characterized in terms of flow instability using peak stress with the help of Lyapunov Function. The true stress- strain curves shows that softening occurs at all lower temperature and for entire strain rates of deformation. The instable flow was suggested by negative m value at deformation condition of 700°C (5 and 10 s-1), while s value at 925°C (10 s-1). The combined result of rate of change of m and s with respect to log strain rate suggest that the deformation condition ranges from 725- 780°C (10-1- 10-1 s-1) and 700°C (1- 10 s-1) representing safe domain for stable flow. © (2015) Trans Tech Publications, Switzerland.


Goel S.,Indian Institute of Technology Roorkee | Kumar N.,Indian Institute of Technology Roorkee | Fuloria D.,Indian Institute of Technology Roorkee | Jayaganthan R.,Indian Institute of Technology Roorkee | And 5 more authors.
Journal of Materials Engineering and Performance | Year: 2016

Fracture toughness and mechanical properties of the zircaloy-2 processed by rolling at different temperatures have been investigated, and simulations have been performed using extended finite element method (XFEM). The solutionized alloy was rolled at different temperatures for different thickness reductions (25–85%). Fracture toughness has been investigated by compact tension test. The improved fracture toughness of the rolled zircaloy-2 samples is due to high dislocation density. SEM image of the fractured surface shows the reduction in dimple sizes with the increase in dislocation density due to the formation of microvoids as a result of severe strain induced during rolling. Compact tension test, edge crack, center crack and three-point bend specimen simulations have been performed by XFEM. In XFEM, the cracks are not a part of finite element mesh and are modeled by adding enrichment function in the standard finite element displacement approximation. The XFEM results obtained for compact tension test have been found to be in good agreement with the experiment. © 2016 ASM International


Goel S.,Indian Institute of Technology Roorkee | Keskar N.,Bhabha Atomic Research Center | Jayaganthan R.,Indian Institute of Technology Roorkee | Singh I.V.,Indian Institute of Technology Roorkee | And 3 more authors.
Journal of Materials Engineering and Performance | Year: 2014

Effect of change in strain path by cross rolling up to a true strain of 1.89 has been studied in the present work. The Zircaloy-2 was subjected to solutionising heat treatment at 800 °C in argon environment for 2 h and subsequently quenched in mercury prior to cross rolling at room temperature. The fragmentation of near basal grains due to change in strain path is evident from the EBSD micrographs. The dislocation density in the crossrolled alloy increases with true strain as calculated from the XRD and EBSD data and it is found to be 2.806453 × 1016/m2. (Formula presented.) extension twins are observed initially up to 25% reduction, with the further reduction in thickness, near basal grains are oriented toward the normal direction. These basal grains undergone fragmentation due to changes in strain path upon cross-rolling as observed from KAM and EBSD images. TEM results of the cross-rolled sample confirm the formation of ultrafine and nanograins in the alloy due to orientation of incidental dislocation boundaries in the direction of macroscopic plastic flow and post-annealing treatment of the deformed alloy. A tensile strength of 991 MPa with 7.5% ductility is observed in the 85% cross-rolled alloy. The cross-rolled alloy upon annealing at 400 °C for 30 min improves ductility to 11%. © 2014, ASM International.


Goel S.,Indian Institute of Technology Roorkee | Jayaganthan R.,Indian Institute of Technology Roorkee | Singh I.V.,Indian Institute of Technology Roorkee | Srivastava D.,Bhabha Atomic Research Center | And 2 more authors.
Materials and Design | Year: 2014

The effect of deformation strain at room temperature on the microstructural and mechanical properties of Zircaloy-2 was investigated in the present work. The sample was initially heat treated at 800. °C in argon environment and quenched in mercury prior to rolling. The deformed alloys were characterized by using EBSD and TEM. It reveals the misorientation of incidental grain boundaries (IDBs) due to large plastic strain induced in the sample. The recovery of deformed alloy upon annealing leads to the formation of ultrafine and nanostructured grains in the alloy. The hardness achieved after 85% room temperature rolling (RTR) is found to be 269. HV, while the tensile strength is 679. MPa and 697. MPa in the rolling and transverse direction, respectively. The improvement in strength is due to generation of high dislocation density and ultrafine grains in the deformed alloy with 85% thickness reduction, during rolling. The deformed alloy subjected to annealing at 400. °C for 30. min sample shows increase in ductility (6% and 7.2%) in rolling and transverse direction, respectively, due to the annihilation of dislocations as evident from the TEM study. © 2013 Elsevier Ltd.


Goel S.,Indian Institute of Technology Roorkee | Keskar N.,Bhabha Atomic Research Center | Jayaganthan R.,Indian Institute of Technology Roorkee | Singh I.V.,Indian Institute of Technology Roorkee | And 3 more authors.
Materials Science and Engineering A | Year: 2014

The mechanical properties and microstructural characteristics of ultrafine grained Zircaloy-2 processed by cryorolling (CR) were investigated in the present work. The solutionised Zircaloy-2 was rolled at liquid nitrogen temperature (77. K) with different thickness reductions (25-85%). The dislocation density 〈. ρ〉 in the cryorolled Zircaloy-2 increases with increasing true strain due to the suppression of dynamic recovery. EBSD analysis of CR Zircaloy-2 revealed initial strain hardening, which has occurred due to activation of {101-2}〈1-011〉 tensile and {112-2}〈1-1-23〉 compressive twins during deformation of samples up to 50% strain. The prismatic and basal slips were activated during subsequent deformation. The fraction of low angle boundaries has increased with increasing true strain up to 50% thickness reduction but the fraction of high angle grain boundaries has increased for CR85% alloy. The CR 85% alloy showed hardness and yield strength values of 282 HV and 891. MPa, respectively. The annealed CR 85% alloy showed higher ductility (9.5% and 11.2% in rolling and transverse direction, respectively) as compared to CR 85% alloy. The annealed Zircaloy-2 showed heterogeneous microstructure consisting of ultrafine grains and nanograins. © 2014 Elsevier B.V.


Fuloria D.,Indian Institute of Technology Roorkee | Nageswararao P.,Indian Institute of Technology Roorkee | Jayaganthan R.,Indian Institute of Technology Roorkee | Jayaganthan R.,Indian Institute of Technology Madras | And 2 more authors.
Materials Chemistry and Physics | Year: 2016

In the present work, the mechanical behavior of Zircaloy-4 subjected to various deformation strains by multiaxial forging (MAF) at cryogenic temperature (CT) was investigated. The alloy was strained up to different number of cycles, viz., 6 cycles, 9 cycles, and 12 cycles at cumulative strains of 2.96, 4.44, and 5.91, respectively. The mechanical properties of the alloy were investigated by performing the universal tensile test and the Vickers hardness test. Both the test showed improvement in the ultimate tensile strength and hardness value by 51% and 26%, respectively, at the highest cumulative strain of 5.91. The electron backscattered diffraction (EBSD) measurement and transmission electron microscopy (TEM) were used for analyzing the deformed microstructure. The microstructures of the alloy underwent deformation at various cumulative strains/cycles showed grain refinement with the evolution of shear and twin bands that were highest for the alloy deformed at the highest number of cycles. The effective grain refinement was due to twins formation and their intersection, which led to the improvement in mechanical properties of the MAFed alloy, as observed in the present work. © 2015 Elsevier B.V.

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