Directional recrystallization and microstructures of an Fe-6.5wt%Si alloy
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ang Chena) Engineering Research Center of Materials Behavior and Design, Ministry of Education, Nanjing University of Science and Technology, Nanjing 210094, People’s Republic of China; and Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831
Hongbin Beib) Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831
Feng Li Engineering Research Center of Materials Behavior and Design, Ministry of Education, Nanjing University of Science and Technology, Nanjing 210094, People’s Republic of China
Feng Ye State Key Laboratory for Advanced Metals and Materials, University of Science & Technology Beijing (USTB), Beijing 100083, People’s Republic of China
Guoliang Chen Engineering Research Center of Materials Behavior and Design, Ministry of Education, Nanjing University of Science and Technology, Nanjing 210094, People’s Republic of China; and State Key Laboratory for Advanced Metals and Materials, University of Science & Technology Beijing (USTB), Beijing 100083, People’s Republic of China
Chain-Tsuan Liu Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831; and Mechanical Engineering Department, Hong Kong Polytechnic University, Hong Kong (Received 18 March 2009; accepted 23 April 2009)
Directional recrystallization of an Fe–6.5wt%Si alloy was investigated by changing hot zone temperatures and growth rates. Elongated (columnar) grains with an aspect ratio more than 10 can be produced when growth parameters are carefully adjusted. It was found that at a fixed growth rate, the grain length and aspect ratio increase with increased hot zone temperatures. At a fixed hot zone temperature, there is a critical growth rate at which columnar grains have the largest average aspect ratio. Below or above this growth rate, the aspect ratio decreases. Texture and grain orientation analysis showed that the preferentially selective growth to form columnar grains was favored by the formation of low-energy surfaces and grain boundaries.
I. INTRODUCTION
Directional recrystallization by zone annealing, where the sample travels through a furnace (hot zone) with a steep temperature gradient, has been used to obtain desirable microstructures in various materials, including oxide dispersion-strengthened materials,1–9 pure metals,10–16 and alloys.17,18 Columnar grain structures or Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/JMR.2009.0303 2654
http://journals.cambridge.org
J. Mater. Res., Vol. 24, No. 8, Aug 2009 Downloaded: 03 Apr 2015
single crystals can be produced by selective grain growth and competitive migrations of grain boundaries. Therefore, this method has been recognized as a powerful technique to control microstructures by optimizing the processing parameters, such as hot zone temperature (HZT), growth rate (V), and temperature gradient (G). The temperature gradient is normally determined by the experimental setup, e
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