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Decomposition Reactions and Toughening in NiAl-Cu Alloys

Published online by Cambridge University Press:  21 February 2011

W. P. Allen ,
J. C. Foley ,
R. F. Cooper  and
J. H. Perepezko
W. P. Allen
Affiliation:
University of Wisconsin, Department of Materials Science and Engineering 1509 University Avenue, Madison, WI 53706
J. C. Foley
Affiliation:
University of Wisconsin, Department of Materials Science and Engineering 1509 University Avenue, Madison, WI 53706
R. F. Cooper
Affiliation:
University of Wisconsin, Department of Materials Science and Engineering 1509 University Avenue, Madison, WI 53706
J. H. Perepezko
Affiliation:
University of Wisconsin, Department of Materials Science and Engineering 1509 University Avenue, Madison, WI 53706
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Abstract

In the NiAl-Cu3 Al pseudobinary section of the Ni-Al-Cu ternary system, the structural similarity of the binary phases yields a miscibility gap between NiAl (B2 structure with ao≃0.2880 nm) and Cu3 Al (bcc structure above 567° C with ao≃0.2946 nm). Due to the extensive mutual solubility, alloys can be solution-treated as single-phase NiAl and then aged at temperatures within the miscibility gap to investigate possible decomposition reactions. Several NiAl-Cu alloys (containing up to 30 at% Cu) were solution-treated at 1000° C, water-quenched, and then aged at either 475° C or 525° C. The decomposition of the supersaturated NiAl was characterized using XRD and SEM. A modulated microstructure was observed for an initial aging of 24 hours, and is consistent with the presence of a conditional spinodal between the NiAl and the Cu3Al. Long term aging resulted in the formation of equilibrium fcc Cu-rich precipitates. In comparison with the brittle nature of the as-quenched samples, the initial aging treatment yields samples which exhibit extensive slip development during hardness testing. Analysis of the deformation/fracture zone produced with a diamond cone indenter suggests that the ductile phase produced by the aging treatment, yielding an in-situ composite, enhances the resistance of NiAl to both crack initiation and propagation.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 194: Symposium R – Intermetallic Matrix Composites I , 1990 , 405
Copyright
Copyright © Materials Research Society 1990

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