High-strength bulk Al-based bimodal ultrafine eutectic composite with enhanced plasticity
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Norbert Mattern and Uta Ku¨hn Leibniz Institute for Solid State and Materials Research Dresden, Institute for Complex Materials, D-01171 Dresden, Germany
Ju¨rgen Eckerta) Leibniz Institute for Solid State and Materials Research Dresden, Institute for Complex Materials, D-01171 Dresden, Germany; and TU Dresden, Institute of Materials Science, D-01062 Dresden, Germany
Ki Buem Kim Department of Advanced Materials Engineering, Sejong University, Seoul 143-747, Republic of Korea
Won Tae Kim Division of Applied Science, Cheongju University, Cheongju 360-764, Republic of Korea
Kamanio Chattopadhyay Department of Metallurgy, Indian Institute of Science, Bangalore 560-012, India
Do Hyang Kimb) Center for Non-Crystalline Materials, Department of Metallurgical Engineering, Yonsei University, Seoul 120-749, Republic of Korea (Received 23 January 2009; accepted 30 March 2009)
An in situ bulk ultrafine bimodal eutectic Al–Cu–Si composite was synthesized by solidification. This heterostructured composite with microstructural length scale hierarchy in the eutectic microstructure, which combines an ultrafine-scale binary cellular eutectic (a-Al + Al2Cu) and a nanometer-sized anomalous ternary eutectic (a-Al + Al2Cu + Si), exhibits high fracture strength (1.1 0.1 GPa) and large compressive plastic strain (11 2%) at room temperature. The improved compressive plasticity of the bimodal-nanoeutectic composite originates from homogeneous and uniform distribution of inhomogeneous plastic deformation (localized shear bands), together with strong interaction between shear bands in the spatially heterogeneous structure.
I. INTRODUCTION
Recently, in situ bulk nanostructure-dendrite composites that simultaneously combine high strength and good plasticity have been highlighted because of their unique mechanical properties and easy manufacturing process (simple single step casting).1–3 These appealing properties can be introduced by bimodal microstructure distribution with micrometer-sized dendrites embedded in the matrix of nano-/ultrafine-scale eutectics. The high strength is a)
This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs. org/jmr_policy b) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0297 J. Mater. Res., Vol. 24, No. 8, Aug 2009
provided by the nano-/ultrafine eutectic matrix, whereas the enhanced plasticity stems from the inhomogeneous microstructure that suppresses deformation instability.4–7 Plastic deformation of these composite materials occurs through a combination of dislocation-based slip in the dendrites and constraint multiple shear banding in the nanostructured matrix.8–16 In this scenario, it is possible to assume that, in general, a bimodal distribution of constituent phases and length scales can be beneficial for the room temperature plastic deformability of high-strength nanostructured materials. However, there have been
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