Ductile-Phase Toughening in TiB w /Ti-Ti 3 Al Metallic-Intermetallic Laminate Composites
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The intermetallic compound a2-Ti3Al has potential as a lightweight material for high-temperature structural applications, exhibiting both high strength, and resistance to oxidation and creep. However, poor ductility and toughness at room temperature prohibit the potential applications in most fields.[1,2] Various approaches have been employed in attempts to improve the toughness of intermetallic compounds, including introducing particles, fibers, or layers of ductile inclusions.[3–7] However, for a given volume fraction, ductile phase inclusions in the laminate form provide the maximum toughening efficiency, followed by fiber and particulate inclusions.[4,6] Metallic-intermetallic laminate (MIL) composites can be fabricated by deposition or bonding the components. Deposition techniques, involving atomic scale transport of the component materials, are relatively costly and slow, HAO WU, Ph.D. Student, LIN GENG, Professor, GUOHUA FAN, Associate Professor, XIPING CUI, Researcher, and MENG HUANG, Master Student, are with the School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, P.R. China. Contact e-mail: [email protected] BO CHENG JIN, Ph.D. Student, RODRIGO MIER HICKS, Master Student, and STEVEN NUTT, Professor, are with the Department of Chemical Engineering and Materials Science, M.C. Gill Composites Center, University of Southern California, Los Angeles, CA 90089-0241. Manuscript submitted March 22, 2015 Article published online June 24, 2015 METALLURGICAL AND MATERIALS TRANSACTIONS A
and thus are not practical for production of large-scale components.[8,9] In contrast, reaction bonding of metallic foils afford multiple advantages, in particular the generation of well-bonded interfaces between the metal and the intermetallic components.[10,11] Furthermore, the laminated structure of the composite allows for variations in layer thickness and volume fractions of the components simply through the selection of initial foil thickness.[4,11,12] In the present work, we explore the concept of ductilephase toughening of Ti3Al by fabrication of MIL composites. In particular, we prepare MIL composites comprising alternating layers of TiBw/Ti and Ti3Al by reaction annealing TiBw/Ti foils and Al foils. Compared with pure Ti, TiBw/Ti has a greater yield strength with little sacrifice of ductility, an important attribute to satisfy the service requirements of high-temperature materials.[13] We also assess both the synthesis process and deformation behavior of the resulting TiBw/TiTi3Al MIL composites. The MIL composites were fabricated by an in situ method, in which alternating Al foils (100 lm thick) and 5 vol pct TiBw/Ti composite foils (500 lm thick) were stacked, followed by hot pressing at 788 K (515 C) under 75 MPa for 1.5 hours and reaction annealing under controlled temperature and pressure (Figure 1). Typical processing parameters for reaction annealing consisted of (i) an initial annealing at 943 K (670 C) for 3 hours to consume all of Al, and (ii) a densification treatment at 1473 K (12
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