Formation of a Nanostructure in a Low-carbon Steel Under High Current Density Electropulsing
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Formation of a nanostructure in a low-carbon steel under high current density electropulsing Yizhou Zhou, Wei Zhang, Manling Sui, Douxing Li, Guanhu He, and Jingdong Guoa) Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China (Received 26 September 2001; accepted 24 January 2002)
The microstructure of a low-carbon steel after high current density electropulsing treatment was characterized by high-resolution transmission electron microscopy. It was found that nanostructured ␥–Fe could be formed in the coarse-grained steel after the electropulsing treatment. The mechanism of the formation of a nanostructure was discussed. It was thought that change of the thermodynamic barrier during phase transformation under electropulsing was a factor that cannot be neglected. It was reasonable to anticipate that a new method might be developed to produce nanostructured materials directly from the conventional coarse-grained crystalline materials by applying high current density electropulsing. Most nanocrystalline (nc) metal samples are very brittle.1–3 Many of these disappointing experimental results can be attributed to artifacts, which are present in nc samples that were induced during sample processing procedures, such as imperfect bonding and/or porosity, contamination, and large microstrain.4 To improve mechanical properties of nc samples, it is compulsory to develop the methods that can prepare pure and dense nc samples with a minimized defect density. Recently, Zhang et al. found that nanophases can be formed in the conventional coarse-grained polycrystalline Cu–Zn alloy by applying high current electropulsing.5 Since the nanophases were directly produced from the coarse-grained material, many of above problems during processing of nc samples can be avoided, so the method of applying high current electropulsing can be anticipated to serve as a potential processing approach to synthesize pure and dense nc samples with a minimized defect density. However, it is necessary to study whether the same or similar results can be obtained in other materials, and the mechanism of the formation of nanophases under electropulsing is also required to be studied more deeply. Because the above paper5 only considered the Joule heating effect of electropulsing and considered that the function of electropulsing was only to supply the temperature rise needed by phase transformation, rapid cooling was the main reason for the formation of nanophases. One challenge for the explanations is whether nanophases can be
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Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 17, No. 5, May 2002
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formed in the above alloy when it is heated over the phase transformation temperature by common heating methods and then rapidly cooled. In this work, we will explore whether or not nanocrystallites of iron can be formed from a coarse-grained low-carbon steel by applying el
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