DISCLAIMER This repon was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employe#, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus. product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any

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... commercial product, proc+ss, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, m mmendation, or favoring by the United States Government or any agency thereof. 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 fiom 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 fiom 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.