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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. Source


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. Source


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. Source


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. Source


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. Source

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