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Crystals 2017, 7(4), 100;

Morphology of Spherulites in Rapidly Solidified Ni3Ge Droplets

School of Chemical & Process Engineering, University of Leeds, Leeds LS2 9JT, UK
Author to whom correspondence should be addressed.
Academic Editor: Eamor M. Woo
Received: 26 January 2017 / Revised: 22 March 2017 / Accepted: 29 March 2017 / Published: 1 April 2017
(This article belongs to the Special Issue Crystal Morphology and Assembly in Spherulites)
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The congruently melting, single phase, L12 intermetallic β-Ni3Ge has been subject to rapid solidification via drop-tube processing. Four different cooling rates are used in this process, at very low cooling rates (≥850 μm diameter particles, ≥700 K s−1) and slightly higher cooling rates (850–500 μm diameter particles, 700–1386 K s−1) the dominant solidification morphology, revealed after etching, is that of isolated spherulites in an otherwise featureless matrix. At higher cooling rates, (500–300 μm diameter particles, 1386–2790 K s−1 and (300–212 μm diameter particles, 2790–4600 K s−1) mixed spherulite and dendritic morphologies are observed. Indeed, at the higher cooling rate dendrites with side-branches composed of numerous small spherulites are observed. Selected area diffraction analysis in the TEM indicate that the formation of spherulites is due to an order-disorder transformation. Dark-field TEM imaging has confirmed that the spherulites appear to consist of lamellae of the ordered phase, with disordered material in the space between the lamellae. The lamellar width within a given spherulite is constant, but the width is a function of cooling rate, with higher cooling rates giving finer lamellae. As such, there are many parallels with spherulite growth in polymers. View Full-Text
Keywords: intermetallics; rapid solidification; microstructure and order-disorder; spherulites; crystal growth intermetallics; rapid solidification; microstructure and order-disorder; spherulites; crystal growth

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Haque, N.; Cochrane, R.F.; Mullis, A.M. Morphology of Spherulites in Rapidly Solidified Ni3Ge Droplets. Crystals 2017, 7, 100.

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