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- 저자 : ( Naoki Takata ) (검색결과 2 건)
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Nanostructured Bulk Copper Fabricated by Accumulative Roll Bonding
Takata, Naoki,Lee, Seong-Hee,Lim, Cha-Yong,Kim, Sang-Shik,Tsuji, Nobuhiro American Scientific Publishers 2007 Journal of Nanoscience and Nanotechnology Vol.7 No.11
<P>In this study, we tried to fabricate the nanostructured bulk copper alloys by a severe plastic deformation process. The sheets of copper alloys (OFC, PMC90, and DLP) were heavily deformed to an equivalent strain of 6.4 by the accumulative roll-bonding (ARB) process. The microstructure and the mechanical property of the fabricated specimens were systematically investigated. The microstructure was finely subdivided with increasing the equivalent strain by the ARB process. The severely deformed copper alloys exhibited the ultrafine lamellar boundary structure where the mean lamella spacing was about 200 nm. The strength significantly increased with decreasing the lamella spacing in the ARB processed copper alloys. Especially, the tensile strength of the DLP alloys ARB processed by 8 cycles (the equivalent strain of 6.4) reached to 520 MPa, which was about three times higher than that of same materials with conventional grain size of 10-100 <I>μ</I>m. On the other hand, the total elongation greatly dropped only by 1 ARB cycle corresponding to an equivalent strain of 0.8, which was around 3%. However, the total elongation increased again with increasing the number of the ARB cycle, and it reached to 10% after 8 cycles. The recovery of the total elongation could be recognized in all studied copper alloys. The obtained stress-strain curves showed that the improvement of the total elongation was caused by the increase in the post-uniform elongation. It can be concluded that the nanostructured copper alloys sheets having high strength without a large loss of ductility could be fabricated by the ARB process.</P>
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( Naoki Takata ),( Hiroki Yokoi ),( Dasom Kim ),( Asuka Suzuki ),( Makoto Kobashi ) 한국부식방식학회 2024 Corrosion Science and Technology Vol.23 No.2
An attempt was made to apply digital image correlation (DIC) strain analysis to in-situ scanning electron microscopy (SEM) observations of bending deformation to quantify local strain distribution inside a ZnMgAl-alloy coating in deformation. Interstitial-free steel sheets were hot-dipped in a Zn-3Mg-6Al (mass%) alloy melt at 400 ℃ for 2 s. The specimens were deformed using a miniature-sized 4-point bending test machine inside the SEM chamber. The observed in situ SEM images were used for DIC strain analysis. The hot-dip ZnMgAl-alloy coating exhibited a solidification microstructure composed of a threephase eutectic of fine Al (fcc), Zn (hcp), and Zn<sub>2</sub>Mg phases surrounding the primary solidified Al phases. The relatively coarsened Zn<sub>2</sub>Mg phases were locally observed inside the ZnMgAl-alloy coating. The DIC strain analysis revealed that the strain was localized in the primary solidified Al phases and fine eutectic microstructure around the Zn<sub>2</sub>Mg phase. The results indicated high deformability of the multi-phase microstructure of the ZnMgAl-alloy coating.
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