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Microstructures and Mechanical Properties of in-situ V-V3B2 Composites

Published online by Cambridge University Press:  26 February 2011

Sujing Xie
Affiliation:
sxie@utk.edu, The University of Tennessee, Department of Materials Science and Engineering, 3700 Sutherland Ave., Knoxville, TN, 37996, United States
Easo P. George
Affiliation:
georgeep@ornl.gov, The University of Tennessee, Department of Materials Science and Engineering, Knoxville, TN, 37996, United States
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Abstract

A series of binary V-B alloys, with compositions spanning the eutectic, were produced by arc melting and drop casting. Microstructural examination revealed that the fully eutectic structure occurs at V-11B rather than V-15B as reported in the V-B phase diagram (all compositions in at.%). The V-11B eutectic was directionally solidified in an optical floating zone furnace, resulting in a composite microstructure consisting of a V matrix and flake or trigonal shaped V3B2 phase. The boride flake spacing (ë) decreases with increasing growth rate (R), following the relation ë2.56R=C, where C is a constant. TEM observations showed that the orientation relationship between the V and V3B2 phases is given by: [001]V // [001]V3B2 and (100)V // (100)V3B2. The growth direction and the V/V3B2 interface are parallel to the [001] direction and (100) planes in the two phases, respectively. Tensile tests were used to investigate the temperature dependence of the strength and ductility of the composite. At temperatures to 600°C, the yield strength of the eutectic is about 140 MPa higher than that of a commonly used vanadium solid-solution alloy, V-4Cr-4Ti. Surprisingly, the eutectic shows 5% tensile ductility at room temperature which increases to 10% as the test temperature is raised to 800°C.

Type
Research Article
Copyright
Copyright © Materials Research Society 2007

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