Undercooling studies on Nb-Pt and Nb-Si alloys using the 105 meter drop tube |
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Authors: | M B Robinson R J Bayuzick and W H Hofmeister |
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Institution: | * George C. Marshall Space Flight Center, AL 35812, U.S.A. ** Vanderbilt University, Nashville, TN 37235, U.S.A. |
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Abstract: | Niobium-platinum samples of compositions ranging from 16 to 32 at. % have been undercooled to as much as 540 K in the low gravity, containerless environment of the 105 meter drop tube located at the George C. Marshall Space Flight Center. Undercooling was terminated in the Nb-Pt samples by the nucleation and growth of the Nb3Pt phase. In the 16–18 at. % Pt samples, this resulted in samples which are completely Nb3Pt, in contrast to both the equilibrium phase diagram and the non-undercooled samples which formed with Nb dendrites and interdendritic Nb3Pt. Undercoolings for the Nb-Si samples were up to 670 K, which corresponds to 27% of the liquidus temperature or 80% of the estimated hypercooling limit. In the Nb-Si system, a coupled zone was identified as well as a metastable extension of the solubility limit of Si in Nb due to deep undercooling. |
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