The influence of SiC particulates on fatigue crack propagation in a rapidly solidified Al-Fe-V-Si alloy |
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Authors: | T J Sutherland P B Hoffman J C Gibeling |
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Affiliation: | (1) Chevron USA Products Company, 94802 Richmond, CA;(2) Division of Materials Science and Engineering, University of California-Davis, 95616 Davis, CA |
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Abstract: | The fatigue crack propagation properties of a rapidly solidified aluminum alloy are compared with those of a metal matrix
composite (MMC) made of the same base alloy with the addition of 11.5 vol pct SiC particulate. The high-temperature base material,
alloy 8009 produced by Allied-Signal, Inc. (Morristown, NJ), is solidified and processed using powder metallurgy techniques;
these techniques yield a fine-grained, nonequilibrium microstructure. A direct comparison between the fatigue crack propagation
properties of the reinforced and unreinforced materials is possible, because alloy 8009 requires no postprocessing heat treatment.
As a consequence, this comparison reflects the influence of the SiC particulate and not differences in microstructure that
could arise during processing and aging. The experimental data demonstrate that the SiC-reinforced material exhibits modestly
superior fatigue crack propagation properties: slower crack growth rates for a given ΔK, at near-threshold crack growth rates.
Even when the data are corrected for crack closure using an effective stress intensity factor, ΔKeff, the composite exhibits lower crack propagation rates than the unreinforced matrix alloy. Microscopic evidence shows a rougher
fracture surface and a more tortuous crack path in the composite than in the base alloy. It is argued that the lower crack
growth rates and higher intrinsic threshold stress intensity factor observed in the composite are associated with crack deflection
around SiC particles.
Formerly Graduate Research Assistant, University of California-Davis |
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