Effect of impurities (graphite) on the high-temperature creep properties of NiAl |
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| Authors: | Amit Prakash Monte J. Pool |
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| Affiliation: | (1) National Metallurgical Laboratory, 831007 Jamshedpur, India;(2) Department of Materials Science and Metallurgical Engineering, University of Cincinnati, 45221 Cincinnati, Ohio, USA;(3) Present address: Department of Materials Science and Metallurgical Engineering, University of Cincinnati, 45221 Cincinnati, Ohio, USA |
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| Abstract: | Previous high-temperature compression creep studies of NiAl have shown peculiar behaviour in the temperature range 700 to 900° C, which was perhaps due to precipitation of impurities in the matrix. To isolate the  impurity effect, high-purity NiAl samples with 0.15 at% and 0.20 at% carbon (graphite) additions have been creep tested at four temperatures between 700 and 850° C. Addition of graphite has been shown to produce a significant reduction in the creep strength of the alloyS. However, alloys with higher graphite concentrations have shown better creep resistance than those with lower graphite concentrations. Transmission electron microscopy indicates the presence of competing softening and hardening mechanisms in the alloys. Softening is due to the graphite particles acting as a dislocation source. Hardening results from a grain-boundary hardening mechanism due to the graphite particles segregating at grain boundaries and a dislocation-impurity (fine graphite) interaction, developing a Cottrell-like atmosphere. |
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