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Formation of a Metastable BCC Solid Solution and Decomposition to a C15 Laves Phase in Melt-Spun CrNb10Ti10

Published online by Cambridge University Press:  10 February 2011

Katherine C. Chen ,
Paul G. Kotula ,
Fuming Chu  and
Dan J. Thoma
Katherine C. Chen
Affiliation:
Materials Science and Technology Division, Mail Stop G755Los Alamos National Laboratory, Los Alamos, NM 87545, USAkchen@lanl.gov
Paul G. Kotula
Affiliation:
Materials Science and Technology Division, Mail Stop G755Los Alamos National Laboratory, Los Alamos, NM 87545, USAkchen@lanl.gov
Fuming Chu
Affiliation:
Materials Science and Technology Division, Mail Stop G755Los Alamos National Laboratory, Los Alamos, NM 87545, USAkchen@lanl.gov
Dan J. Thoma
Affiliation:
Materials Science and Technology Division, Mail Stop G755Los Alamos National Laboratory, Los Alamos, NM 87545, USAkchen@lanl.gov
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Abstract

A metastable, disordered bcc phase has been formed from the melt in a Cr-rich alloy of the Nb-Cr-Ti system, where large volume fractions of the Laves phase would develop under equilibrium solidification conditions. X-ray diffraction (XRD) studies and lattice constant determinations confirm that the melt-spun ribbons contain a bcc phase beyond its terminal solid solution limits. Solidification pathways are proposed based upon metastable and equilibrium phase diagrams. Microstructures have been studied using optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Cross-sectional TEM reveals tiny, dispersed Laves phase precipitates within the metastable bcc grains near the chill (wheel) side. Away from the wheel, the microstructure changes to a dendritic structure of the bcc and C15 Laves phase. Annealing of the melt-spun ribbons produces a fine, two-phase microstructure of the equilibrium phases. Microstructures from the melt-spun and arc-melted processing conditions are compared. The microstructural control afforded through this metastable processing route enables a methodology to tailor phase distributions for optimized toughness in Laves phase alloys.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 481: Symposium P – Science and Technology of Semiconductor Surface Preparation , 1997 , 89
Copyright
Copyright © Materials Research Society 1998

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References

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