Evolution of Constitution, Structure, and Morphology in FeCo-Based Multicomponent Alloys
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IT is well known that bulk metallic glasses (BMGs) are a family of advanced ultrahigh strength materials, which have been investigated intensively.[1–3] However, the intrinsic brittleness and strict fabrication conditions of these BMGs limit their further application as advanced structural materials.[4] Recently, dendriteeutectic (D-E) composites were developed in Ti-, Fe-, Cu-, Mg-, and Al-based chill-cast multicomponent hypoeutectic alloys as a competitive replacement of BMGs.[5–12] Compared to the BMGs with close chemical compositions, this kind of D-E composite shows similar strength and remarkable plasticity as well as a more controllable production process. Normally, the microstructure of the hypoeutectic alloys is characteristic of soft dendrite (a terminal solid solution phase of basis element) embedded into hard eutectics (a networklike framework phase). Many reports indicate that the outstanding mechanical properties can be related to the composite structure of soft and hard phases with appropriate morphology and deformation behavior.[5,6,8,9,13] Since most of the valuable information for hypoeutectic alloys is focused in binary, ternary, and a few conventional multicomponent systems, the investigation of phase constituent and microstructural evolution dependent on chemical composition in multicomponent alloys may reveal information about R. LI, Guest Scientist, M. STOICA, Research Staff Member, and G. LIU, Guest Scientist, are with the Institute for Complex Materials, IFW Dresden, D-01171 Dresden, Germany. Contact e-mail: m.stoica@ ifw-dresden.de J. ECKERT, Professor, is with the Institute for Complex Materials, IFW Dresden, and the Institute of Materials Science, TU Dresden, D-01062 Dresden, Germany. This article is based on a presentation given in the symposium ‘‘Bulk Metallic Glasses VI,’’ which occurred during the TMS Annual Meeting, February 15–19, 2009, in San Francisco, CA, under the auspices of TMS, the TMS Structural Materials Division, TMS/ASM: Mechanical Behavior of Materials Committee. Article published online November 24, 2009 1640—VOLUME 41A, JULY 2010
controlling the morphological structure and optimizing the mechanical properties of this kind of D-E composite. Most recently, we produced a family of FeCo-based D-E composites with high strength and large plasticity through adding eutectic-forming elements (i.e., Mo, C, B, and Si) with fixed atomic ratios into equiatomic FeCo alloy by copper mold casting.[13] Compared to the brittle binary precursor alloy, these chill-cast FeCobased multicomponent alloys exhibit remarkable improvement of yield strength and plastic deformation. In this article, we evaluated the effect of composition adjustment on thermal properties, phase constituent, and morphological characteristics of (Fe0.5Co0.5)x(Mo0.1C0.2B0.5Si0.2)100–x (x = 95, 90, 85, 80, and 70) alloys. The forming condition and morphology of metastable phases in our alloys will be discussed. A possible evolution of constituent phases and microstructure for the x = 95, 90, and 85 alloys during th
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