Titanium-Based Metallic Glass Composites with Good Plasticity
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TRODUCTION
TI-BASED bulk-metallic glasses (BMGs) have received increased attention in recent years because of their outstanding mechanical properties (such as large elastic strain (~2 pct), high strength (~2 GPa), and low density) for structural applications.[1–3] In addition, they also draw extensive interest as excellent candidates for biomaterials.[4,5] However, it is known that BMGs usually exhibit low plasticity due to the absence of dislocation activities and strain hardening. Therefore, for commercial applications, it is important to improve their ductility without a sacrifice in the strength. To improve the plasticity of BMGs, extensive research has been done over the past two decades. It has been widely recognized that the low plasticity is caused by inhomogeneous plastic deformation, i.e., the severe shear localization. As a result, the general method is to introduce second phases in the metallic-glass matrix to restrict the rapid propagation of shear bands. Furthermore, these second phases can interact with shear bands and effectively induce multiplication, branching, and FENG JIANG, Postdoctoral Candidate, HONGQI LI, Postdoctor, GUOJIANG FAN, Assistant Professor, and PETER K. LIAW, Professor, are with the Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996-2200, USA. YANDONG WANG, Research Associate, Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996-2200, USA, is Professor, Key Laboratory for Anisotropy Design and Texture Engineering of Materials (Ministry of Education), Northeastern University, Shenyang 110004, PeopleÕs Republic of China. HAHN CHOO, Professor, is with the Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996-2200, USA, and the Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 378306115, USA. This article is based on a presentation given in the symposium entitled ‘‘Bulk Metallic Glasses IV,’’ which occurred February 25– March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee. Article published online November 28, 2007 METALLURGICAL AND MATERIALS TRANSACTIONS A
restriction of shear bands to increase the plasticity of BMGs. The second phases can take many forms, including nanocrystals (quasi-crystals),[6,7] crystalline particles,[8,9] fibers,[10,11] dendritic intermetallic phases,[12] martensite phases,[13] and pores.[14] As a possible route to obtain Ti-based metallic glass composites, the in-situ partial crystallization and the addition of second phases have been investigated. The former approach can be realized by changing the composition[15–17] or heating the as-cast alloys[6,18] to achieve metallic glass composites. The latter one is obtained by adding refractory metal crystals into amorphous matrices.[19] In the literature, the first method is chosen as an effective method of easily introducing second phases (nanocrystals, crystals, and dendritic intermeta
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