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Metals 2017, 7(6), 187; doi:10.3390/met7060187

Phase Selection during Solidification of Ni-10.95 at. % and B-3.23 at. % Si Alloy

1
Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Saltillo, 25900 Ramos Arizpe, Coahuila, Mexico
2
Instituto Tecnológico de Saltillo, 25280 Saltillo, Coahuila, Mexico
3
Fundición de Aleaciones Especiales de Mexico S. A. de C.V., 25100 Saltillo, Coahuila, Mexico
*
Author to whom correspondence should be addressed.
Academic Editor: Anders E.W. Jarfors
Received: 13 February 2017 / Revised: 27 April 2017 / Accepted: 16 May 2017 / Published: 24 May 2017
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Abstract

To gain insight into the solidification of the Ni-10.95 at. % and B-3.23 at. % Si alloy, 29 cast samples extracted from a casting of this alloy were remelted under an Ar atmosphere, using either DSC or an in-house thermal analysis apparatus. Ni(fcc) and Ni3B phases were identified by X-ray diffraction of both the remelted and original cast samples; however, microstructural differences were observed between the two. These microstructural differences are associated with the high undercooling observed during the eutectic reaction in the remelted samples. This high undercooling results from the difficulty of Ni3B nucleation, which allows the formation of a NixBy metastable phase. Metallographic inspection shows that the metastable phase solidifies at least partially through a non-cooperative growth mechanism. This metastable phase may be the elusive Ni23B6 phase. The melting temperature of the metastable phase is 985 °C, and it solidifies below 943 °C under the experimental conditions used in this study. The temperature of solid transformation of the metastable constituent to Ni3B and Ni is strongly dependent on the amount of Ni3B formed during solidification. The minimal temperature of such transformation, 834 °C, corresponds to samples where Ni3B solidification was not detected in the thermal curves. View Full-Text
Keywords: thermal analysis; microstructure; metastable phase thermal analysis; microstructure; metastable phase
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MDPI and ACS Style

Fraga-Chávez, K.L.; Castro-Román, M.J.; Herrera-Trejo, M.; Ramírez-Vidaurri, L.E.; Aguilera-Luna, I. Phase Selection during Solidification of Ni-10.95 at. % and B-3.23 at. % Si Alloy. Metals 2017, 7, 187.

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