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Structural superplasticity in a fine-grained eutectic intermetallic NiAl-Cr alloy

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Frommeyer,  G.
Materials Technology, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society;

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Rablbauer,  R.
Innovative Steel Research, Materials Technology, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society;

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Frommeyer, G., Kowalski, W., & Rablbauer, R. (2007). Structural superplasticity in a fine-grained eutectic intermetallic NiAl-Cr alloy. Metallurgical and Materials Transactions A, 37A, 3511-3517.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0019-5590-3
Abstract
A rapidly solidified and thermomechanically processed fine-grained eutectic NiAl-Cr alloy of the composition Ni33Al33Cr34 (at %) exhibits structural superplasticity in the temperature regime from 900 °C to 1000 °C at strain rates ranging from 10-5 to 10-3 s-1. The material consists of a B2-ordered intermetallic NiAl(Cr) solid solution matrix containing a fine dispersion of bcc chromium. A high strain-rate-sensitivity exponent of m = 0.55 was achieved in strain-rate-change tests at strain rates of about 10-4 s-1. Maximum uniform elongations up to 350 % engineering strain were recorded in superplastic strain to failure tests. Activation energy analysis of superplastic flow was performed in order to establish the diffusion-controlled dislocation accommodation process of grain boundary sliding. An activation energy of Qc = 288 ± 15 kJ/mole was determined. This value is comparable with the activation energy of 290 kJ/mole for lattice diffusion of nickel and for 63Ni tracer self-diffusion in B2-ordered NiAl. The principal deformation mechanism of superplastic flow in this material is grain-boundary sliding accommodated by dislocation climb controlled by lattice diffusion, which is typical for class II solid-solution alloys. Failure in superplastically strained tensile samples of the fine-grained eutectic alloy occurred by cavitation formations along NiAl || Cr interfaces.