Fatigue crack growth through alloyed niobium, Nb-Cr2Nb, and Nb-Nb5Si3
in situ composites |
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Authors: | David L Davidson |
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Affiliation: | (1) Materials Engineering Department, Southwest Research Institute, 78228 San Antonio, TX |
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Abstract: | Fatigue cracks were grown through several niobium-based materials. For Nb-Cr-Ti composition materials, the single-phase alloy
represented the matrix of two in situ composites with about 22 and 38 vol pct Cr2Nb. Grain boundaries were coated with intermetallic in the lower-volume fraction material, while the 38 vol pct Cr2Nb composite consisted of mainly spherical, dispersed intermetallic. The Nb-10Si composite was composed of about 28 vol pct
primary Nb5Si3, with most of the matrix alloy in “fiberlike” shapes due to extrusion. Crack growth rates through the composites were generally
faster than for unalloyed Nb, roughly in proportion to the volume fraction of intermetallic, although differences in microstructure
make this comparison difficult. The presence of intermetallic greatly alters deformation of material near the crack tip. Particles
of Cr2Nb were broken during the crack growth process, leading to increased crack growth rates. These results suggest microstructural
modifications that could be expected to enhance fatigue crack growth resistance. |
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