Superplastic behavior of a kappa carbide material (Fe 3 AlC x )
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Superplastic behavior of a kappa carbide material (Fe3 AlCx ) Woo-Jin Kim Department of Metallurgy and Materials Science, Hong-Ik University, 72-1 Sangsu-Dong, Mapo-Ku, Seoul, 121-791, Korea
Oscar A. Ruano Department of Physical Metallurgy, CENIM, C.S.I.C., Av. Gregorio del Amo 8, 28040 Madrid, Spain
Jeffrey Wolfenstine Department of Chemical and Biochemical Engineering, University of California, Irvine, California 92717
Georg Frommeyer Max Planck Institut f¨ur Eisenforschung, GmbH, Max Planck Strasse 1, D-40237, Germany
Oleg D. Sherby Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (Received 5 November 1995; accepted 8 May 1997)
Fine-grained kappa carbide (Fe3 AlCx ) materials, containing 12.5 and 14% Al, and 3.5% C, were prepared by powder processing and hipping procedures. The creep behavior of the kappa materials was shown to be identical to that observed in superplastic iron carbide, and was shown to follow a grain boundary–diffusioncontrolled grain boundary sliding relation. The tensile fracture strains in kappa, however, were shown to be considerably less than in iron carbide with a maximum elongation of 92% noted. This difference is attributed to either a low stress intensity factor or to contamination of the powder surface in the kappa material. The compression creep strength, at a given strain rate, was shown to be about two times higher than the tension creep strength.
I. INTRODUCTION
The use of powder metallurgy and rapid solidification technologies allows a widening of the application of materials as a result of the fine microstructures that can be produced by these routes. For iron-aluminum-carbon alloys in particular, it allows achieving fine metastable structures.1 Aluminum, a ferrite stabilizer, can be added to cast iron and iron alloys to increase the corrosion resistance, replacing chromium which is a strategic material. The ternary phase, Fe3 AlCx (kappa), forms in the composition range 1 to 4.5% C and 8 to 23% Al. The kappa carbide, Fe3 AlCx (x ranges between 0.5 and 1), has an ordered fcc structure (AuCu3 or L12 -type structure) with C atoms in interstitial positions.2 Superplasticity studies on fine-grained high aluminum, high-carbon iron alloys have been previously performed. Fukuyo et al.3 studied a 10% Al, 1.3% C iron alloy, and showed superplastic behavior at 800 to 1100 ±C with elongations of over 1000% recorded. The major phase was ferrite or austenite with a relatively small volume fraction of kappa (about 24%). Wittenauer et al.4 showed that such a material could be formed into a complex shape component by superplastic forming. Teo et al.5 studied a 10% Al, 1.9% C iron alloy and showed J. Mater. Res., Vol. 12, No. 9, Sep 1997
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that high tensile elongations, exceeding 1000%, could be obtained for this material when fine-grained. The material contained 50 vol. % of ferrite and 50 vol. % of kappa. It is the purpose of this investigat
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