Fabrication and Mechanical Characterization of Ti-Based Metallic Glass Matrix Composites by the Bridgman Solidification
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INTRODUCTION
BULK metallic glasses (BMGs) with the long-rangedisordered and the short-range-ordered atomic arrangement have incomparable properties to their crystalline counterparts.[1–5] However, unlike the crystalline alloys with considerable plasticity through strain hardening and recovery mechanisms, BMGs lack such mechanisms due to highly localized shear deformation, which results in the poor ductility and catastrophic failure during loading, and severely limits their further applications.[1,5] In the past few years, metallic glass matrix (MGM) composites, including ex situ particles or fibers and in situ nanocrystallines or dendrites, as the successful attempts, were made to alleviate the poor ductility of BMGs.[3–10] Especially, in situ MGM composites have combined distinguished plasticity and high strength by introducing ductile dendrites into glassy matrix and the strong interface, e.g., La-,[11,12] Zr-,[1,13–15] Ti-,[2,16,17] Cu-,[18,19] and Mg-MGM composites.[20] Among these composites, Ti-based MGM composites for the combination of the remarkable properties of Ti-based BMGs and titanium alloys, such as the excellent glass formation ability, high strength, good toughness, and low elastic modulus and density, etc., have motivated further research for high-performance applications in the fields of automotive, aerospace, and engineering.[2,15,16,20] Microscopically, many results indicated that the mechanical properties of in situ MGM composites have strongly depended on the microstructure characteristics, including morphology, distribution, interspacing, size (l), and volume fraction (Vf) of dendrites.[1,2,11–20] Compared with other processes, the Bridgman solidification Y.S. WANG, Ph.D. Candidate, G.J. HAO, Researcher, Y. ZHANG, and J.P. LIN, Professors, are with the State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, P.R. China. Contact e-mail: linjunpin@ustb. edu.cn J.W. QIAO, Associate Professor, is with the Laboratory of Applied Physics and Mechanics of Advanced Materials, College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, P.R. China. Manuscript submitted April 27, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS A
not only has been recognized as a technique offering several advantages, e.g., the uniform microstructures for prevention of macrosegregation and porosity, but also can tailor [21–23] microstructures by controlling processing Therefore, the Bridgman solidification parameters. has been widely used to tailor the microstructure and mechanical properties of MGM composites, e.g., Pd-,[24] La-,[12] Zr-,[25,26] Ti-,[17] etc. In this study, Ti-based MGM composites were fabricated using the Bridgman solidification with a graphite heater, which is different from the previous process.[21–23] The microstructure, mechanical properties, and their relationship were characterized.
II.
EXPERIMENTAL PROCEDURE
A. Material Fabrication First, the master alloys with composition of Ti47Zr19Be15V12Cu7 (at. pct
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