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  • 1
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    Liquidus Temperatures and Solidification Behavior in the Copper-Niobium System (1998)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: The copper-niobium phase diagram has been under active debate; thus, a corroboratory experimental study is needed. In this investigation, the melts of Cu-Nb alloys at compositions ranging from 5 lo 86 wt% Nb were processed in different environments and solidified at relatively low rates of 50-75 C/s to determine liquidus temperatures and to study solidification behavior. For all samples processed under very clean conditions, only Nb dendrites in a Cu matrix were observed; while in the presents of oxygen impurities, the alloys containing 5-35 wt% Nb exhibited microstructure of Nb-rich spheroids and Nb dendrites in the Cu matrix. The results obtained from clean conditions are in fair agreement with the Cu-Nb phase diagram having an S-shaped, near-horizontal appearances of the liquidus. The formation of Nb-rich droplets at slow cooling rates is discussed in terms of a stable liquid miscibility gap induced by oxygen.
    Keywords: Metallic Materials
    Type: Acta Materialia (ISSN 1359-6454); Volume 46; No. 11; 3849-3855
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  • 2
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    Direct Determination of the Metastable Liquid Miscibility Gap in Undercooled Cu-Co Alloys (1999)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: Bulk Cu-Co alloys at compositions ranging from 10 to 80 wt pct Co were highly undercooled using a melt fluxing technique. The metastable liquid separation boundary has been directly determined from the measured temperature-time profiles. It was found that the critical point of the miscibility gap is slightly shifted towards the Co side and about 90 K below the liquidus. A droplet-shaped microstructure was observed for all solidified specimens (Cu- 10 to 80 wt pct Co), when the melts were undercooled into the metastable miscibility boundary.
    Keywords: Metallic Materials
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  • 3
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    Metastable Demixing of Supercooled Cu-Co and Cu-Fe Alloys in an Oxide Flux (1998)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A systematic study on the liquid separation in supercooled Cu-Co and Cu-Fe alloys was performed using a melt fluxing which permits high supercooling to be achieved. Moreover, this method renders it possible to directly measure binodal temperatures and establish metastable liquid miscibility gap (LMG). All phase-separated samples at compositions ranging from 10 to 80 wt pct Co or to 83 wt pct Fe were found to exhibit droplet-shaped morphologies, in spite of various droplet distributions. Uniformly dispersed microstructures were obtained as the minority component was less than 20 vol.%; while beyond this percentage, serious coarsening was brought about. Calculations of the miscibility gap in the Cu-Co system and Stokes movement velocity of Co and Fe droplets in Cu matrix were made to analyze the experimental results.
    Keywords: Metallic Materials
    Type: TMS; Feb 15, 1998 - Feb 19, 1998; San Antonio, TX; United States
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  • 4
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    Undercooling, Liquid Separation and Solidification of Cu-Co Alloys (1998)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: Large undercooling can induce not only various solidification pathways, but also a precursor reaction, or liquid separation. This paper deals with the latter effect of undercooling using examples of the Cu-Co system which has a flattened liquidus. Bulk Cu-Co alloys (about 7mm diameter) at compositions ranging from 10 to 90 wt pct Co were highly undercooled using a fluxing technique. Except for Cu-90 wt pct Co, liquid separation was directly observed as undercooling exceeded a critical value depending on the composition. It was also confirmed by a microstructural transition from dendrites to droplets above the critical undercooling. Finally, theoretical calculations regarding the metastable miscibility boundary and maximum droplet radius were made to analyze the experimental results.
    Keywords: Metallic Materials
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  • 5
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    On the Cu-Nb Phase Diagram and Solidified Microstructures (1998)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: Container and containerless processing was employed to determine liquidus temperatures and to examine microstructural development in the Cu-Nb system. The Cu-Nb phase diagram of an S-shaped, near-horizontal liquidus, has been confirmed by both the temperature-time profiles and resultant microstructures with only Nb dendrites in a Cu matrix, which were obtained from crucible experiments under clean conditions. However, the microstructural pathways of Cu-Nb alloys are particularly sensitive to processing variables. By the addition of oxygen impurities or rapid solidification, droplet-shaped morphology was observed for some compositions, implying occurrence of a liquid-phase separation. The effects of impurities and cooling rates are analyzed in connection with a stable and metastable liquid miscibility gap, respectively.
    Keywords: Metallic Materials
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  • 6
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    Liquidus Temperatures and Solidification Behavior in the Copper-Niobium System (1998)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: The copper-niobium phase diagram has been under active debate; thus, a corroboratory experimental study is needed. In this investigation, the melts of Cu-Nb alloys at compositions ranging from 5 to 86 wt pct Nb were processed in different environments and solidified at relatively low cooling rates of 50 to 75 C/s to determine liquidus temperatures and to study solidification behavior. For all samples processed under very clean conditions, only Nb dendrites in a Cu matrix were observed; while in the presence of oxygen impurities the alloys containing 5 to 35 wt pct Nb exhibited microstructure of Nb-rich spheroids and Nb dendrites in the Cu matrix. The results obtained from clean conditions are in fair agreement with the Cu-Nb phase diagram having an S-shaped, near-horizontal appearance of the liquidus. The formation of Nb- rich droplets at slow cooling rates is discussed in terms of a stable liquid miscibility gap induced by oxygen.
    Keywords: Metallic Materials
    Format: text
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