Influence of heterogeneities with different length scale on the plasticity of Fe-base ultrafine eutectic alloys
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Ki Buem Kim Department of Advanced Materials Engineering, Sejong University, Seoul 143-747, Republic of Korea
Min Ha Lee Leibniz Institute for Solid State and Materials Research Dresden, Institute for Complex Materials, D-01171 Dresden, Germany; and Advanced Materials Division, Korea Institute of Industrial Technology, Incheon 406-840, Korea
Won Tae Kim Division of Applied Science, Cheongju University, Cheongju 360-764, Republic of Korea
Jürgen Eckertb) 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 (Received 20 January 2008; accepted 16 April 2008)
The evolution of microstructure and its influence on the mechanical properties of high-strength ultrafine eutectic Fe–(Ti, Zr)–(B, Co) alloys has been studied. The addition of B or Co improves the room temperature compressive plasticity from 1% to ∼8.5% or ∼14%, respectively, due to the formation of a heterogeneous microstructure with distinctly different length scales, which can delay the propagation of shear bands and promotes the activation of multiple shear bands. I. INTRODUCTION
In general, metastable and non-equilibrium materials with either nano- or ultrafine-grained structure with uniform size distribution or a glassy structure with nonperiodic atomic configuration possess ultrahigh strength and hardness compared with conventional coarse-grained materials.1,2 However, these materials suffer from low ductility at room temperature due to their highly localized inhomogeneous plastic deformation.1,2 To improve the plasticity of these materials, the concept of introducing heterogeneities with different length scale and/or crystallinity in the samples has been proposed. For example, short/medium-range ordered clusters,3,4 nano-scale crystalline/quasicrystalline precipitates,5–7 or micrometer-scale ductile dendrites were combined with a glassy matrix,8–10 or two phase glassy alloys induced by phase separation11,12 were produced. Alternatively, a)
Address all correspondence to this author. e-mail: [email protected] b) 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. DOI: 10.1557/JMR.2008.0252 J. Mater. Res., Vol. 23, No. 7, Jul 2008
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nano-composites with bimodal grain size distribution13,14 or nanostructure–dendrite composites consisting of a nanocrystalline matrix and a toughening phase were developed.15–21 In this scenario, it is believed that multiple shear banding and delocalization of major shear bands in glasses or alloys with a nanostructured matrix as well as the evolution of slip in ductile dendrites play an important role to control the macroscopic plasticity.22–24 On the other hand, recent investigations revealed that the length scale heterogeneity of the eutectic colonies in high-strength n
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