A high specific strength, deformation-processed scandium-titanium composite
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MATERIALS RESEARCH A high specific strength, deformation-processed scandium-titanium composite A. M. Russell and Y. Tian Ames Laboratory, Iowa State University, Ames, Iowa 50011
J. D. Rose U.S. Steel Company, Gary, Indiana 46402
T. W. Ellis Kulicke & Soffa Industries, Inc., Willow Grove, Pennsylvania 19090
L. S. Chumbley Ames Laboratory, Iowa State University, Ames, Iowa 50011 (Received 3 June 1998; accepted 20 August 1998)
A 59% Sc–41% Ti deformation-processed metal-metal composite was produced by rolling to a true strain of 2.3 at 873 K followed by cold rolling to a total true strain of 3.6. Rolling reduced the original eutectoid microstructure to lamellae of a –Sc and a –Ti with average lamellar thicknesses of 150 nm (Sc) and 120 nm (Ti). The cold-rolled material had an ultimate tensile strength of 942 MPa and a specific strength of 259 Jyg. The Sc matrix was oriented with the k0001l tilted 22± from the sheet normal direction toward the rolling direction, an unusual texture for an HCP metal with a low cya ratio, which suggests Sc may deform primarily by basal slip.
The light metals Al, Mg, and Ti have seen largescale industrial use for decades, especially in applications where high specific strengths are required. The light metal Sc has received far less research and development attention, even though Sc has a density of only 2990 kgym3 and a melting temperature as high as that of Fe. The primary impediments to greater use of Sc are its high cost and the lack of Sc alloy development work. The high cost of metallic Sc is not a result of inherent scarcity, but results from processing difficulties and lack of demand. In fact, commonly used elements such as Ta, Mo, and W are all considerably scarcer in the earth’s crust than Sc.1 Research in Sc mechanical metallurgy began nearly 40 years ago,2– 6 but has received only limited attention during the ensuing years. In this project, a Sc–Ti deformation processed metal metal composite (DMMC) was produced in an attempt to expand the limited knowledge base of Sc mechanical metallurgy. The authors believe this study is the first attempt to produce a high strength alloy or composite with a Sc matrix. Previous studies of DMMC’s have shown anomalous strengthening in fcc matrix materials such as Cu7–11 and Al.12,13 Work in HCP matrix DMMC’s14,15 has been more limited, but suggests that the ability of HCP metals to be axisymmetrically deformed to large true strains is limited by their tendency to assume texture orientations that permit only plane strain. Texture-induced plane straining would not necessarily be a limitation for rolled DMMC’s, and one of the motivations for this study was 8
http://journals.cambridge.org
J. Mater. Res., Vol. 14, No. 1, Jan 1999
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to determine if anomalously high strengths would result from extensive deformation processing by rolling a twophase Sc –Ti DMMC. The preferred orientation of rolled Sc has not been reported in the literature. Based on the elements’ cya ratios, one might suppose that Sc (cya 1.594) would defo
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