Microstructural Changes by Annealing in Ultrafine-Grained Electrodeposited Pure Iron
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TRODUCTION
YOSHINAGA et al.[1–3] have reported that an electrodeposited pure iron sheet exhibits an ultra-high Lankford (R) value greater than 7.0, which cannot be realized by only well-developed h111i fiber texture along the deposition direction. Recently, we clarified that such a high R value was caused by the operation of specific slip systems coupled with a characteristic grain shape with the h111i fiber texture using in situ neutron diffraction and semi in situ measurements during tensile deformation.[4] The combination of these global and microscopic observations revealed that the texture changes from {111}hhkli to {111}h110i with grain coalescence accompanied by tensile deformation.[4] Hydrogen absorption usually occurs during electrodeposition process of metals and alloys. Choo and Lee[5] have classified trap sites of hydrogen in iron by the activation energy, which increases for grain boundaries, dislocations, and microvoid in order, and claimed that hydrogen existed in the microvoids as a molecule. Thermal desorption spectroscopy (TDS) results suggested that hydrogen was trapped at the above three trapped sites in the present as-deposited pure iron, and small-angle neutron scattering (SANS) revealed that the bubble size increased a little whereas volume fraction decreased by 673 K (400 C) annealing, then following that all the bubbles disappeared by 973 K (700 C) annealing.[6] The outgassing with annealing must stem YUHUA SU, Post Doctoral Fellow, and YO TOMOTA, Professor, are with the Tomota Laboratory, Graduate School of Science and Engineering, Ibaraki University, 4-12-1 Nakanarusawa, Hitachi, Ibaraki 316-8511, Japan. Contact e-mail: [email protected], [email protected] STEFANUS HARJO, Senior Scientist, is with the J-PARC Center, Japan Atomic Energy Agency, 2-4, Shirane Shirakata, Tokai, Ibaraki 319-1195, Japan. Manuscript submitted May 29, 2013. Article published online September 25, 2013 990—VOLUME 45A, FEBRUARY 2014
from decrease in free energy in terms of thermodynamics. In addition, the bubble size and volume fraction were found to decrease with rolling at room temperature, which was likely to be caused by the change in the status of hydrogen location during plastic deformation.[6] Yoshinaga et al.[7] have studied the formation of texture by cold rolling followed by annealing in an electrodeposited pure iron sheet. According to their results, {111}h112i orientated grains predominate in the 65 pct rolled sheet after recrystallization, whereas the texture becomes {111}h110i in the 80 pct rolled sheet. On the other hand, Motegi et al.[8] examined the influence of annealing on tensile behavior and found that the R value decreased with an increase in the annealing temperature. The recrystallization behavior and mechanical properties of high purity iron has also been reported to be affected by the electrodeposition structure, the residual stress induced by the electrodeposition process, and interstitial impurities.[9] Hence, in this paper, changes in the microstructure upon annealing in electrod
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