Effects of precipitated phase and order degree on bending properties of an Fe-6.5 wt%Si alloy with columnar grains
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Qiang Yang Advanced Materials and Technology Institute, University of Science and Technology Beijing, Beijing 100083, People’s Republic of China
Zhihao Zhang and Jianxin Xiea) Advanced Materials and Technology Institute, University of Science and Technology Beijing, Beijing 100083, People’s Republic of China; and State Key Lab for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, People’s Republic of China (Received 17 October 2010; accepted 29 April 2011)
Effects of the precipitated phase and the ordered phase domain of an Fe-6.5 wt%Si alloy before and after heat treatment on the bending properties were investigated in this study. The results showed that original needle-like phases were spheroidized after the heat treatment at 900 °C for 1 h followed by slow or rapid cooling. Compared with the directional solidified sample, the slow cooling sample had a higher order degree, whereas the rapid cooling samples had a lower order degree. After rapid cooling heat treatment, the fracture deflection of the sample was increased by 73.8%. Fracture analysis showed that transition from quasi-cleavage fracture to tear pit-like fracture took place in the rapid cooling sample. The bending properties of the Fe-6.5 wt%Si alloy were improved mainly due to the changes in morphology and amount of the precipitated phase as well as the reduction of order degree.
I. INTRODUCTION
Fe-6.5 wt%Si alloy, as an excellent soft magnetic material, exhibits high permeability, low coercive force, and near-zero magnetostriction.1,2 It has wide application prospects in high frequency fields because of its advantages in reducing the consumption of energy and noise pollution, such as transformers, power generators, and electric relay.3 However, it is impossible to fabricate Fe-6.5 wt%Si alloy thin sheet by the conventional rolling process due to its brittleness at room temperature,4 which impeded its industrial application seriously. Previous studies have reported that the workability of some brittle alloys, such as Ni3Al,5 Ni50Al20Fe30,6 and Al–Si alloy,7 can be improved by directional solidification. This improvement is mainly attributed to the columnar grains with less casting defects, less transverse grain boundaries, and more low-angle grain boundaries, which effectively suppresses the propagation of cracks during deformation. Furthermore, it was reported that B element can effectively reduce brittleness of some intermetallics at room temperature because of its contribution to increases both in bonding energy of grain boundary and density of domain boundary, reduction in the antiphase a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.136 J. Mater. Res., Vol. 26, No. 14, Jul 28, 2011
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domain boundary energy, and the long-range order parameters as well as grain refinement.8–10 Grain size and ordering–disordering phenomena of high-silicon Fe–Si alloys produced by conventional casting or spray forming could
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