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Solidification Processing of NbCr2 Alloys

Published online by Cambridge University Press:  21 February 2011

D. J. Thoma  and
J. H. Perepezko
D. J. Thoma
Affiliation:
University of Wisconsin-Madison, Department of Materials Science & Engineering 1509 University Ave., Madison, WI, 53706 USA
J. H. Perepezko
Affiliation:
University of Wisconsin-Madison, Department of Materials Science & Engineering 1509 University Ave., Madison, WI, 53706 USA
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Abstract

Microstructural development in alloys bordering the NbCr2 Laves phase composition has been evaluated following solidification processing. With splat quenching of binary alloys, rapid solidification has yielded supersaturation of both Nb-rich and Cr-rich primary solid solutions as well as some solubility extension of the C15 phase during cooling as compared to as-cast structures. Ternary additions of Ti are soluble in NbCr2 along the pseudobinary NbCr2-TiCr2 section for C15 structures and completely miscible in bcc Nb and Cr solutions. In the rapid freezing of splats, modest Ti additions to NbCr2 enhance the development of an extended bcc solution during freezing and the supersaturation of the C15 phase during solid-state cooling. In the solid state, the C14–C15 transformation of the Laves phase is suppressed partially in arc-cast ingots and more completely at high cooling rates. Upon heating, thermal analysis has revealed that the retained C14 phase undergoes a decomposition sequence with at least two stages, possibly involving polytypes and associated faulting, to the stable C15 structure. The microstructural options developed by solidification processing, solid state transformations, and alloying have been observed to modify the brittle behavior of the as-cast structures.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 194: Symposium R – Intermetallic Matrix Composites I , 1990 , 105
Copyright
Copyright © Materials Research Society 1990

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