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Metals 2016, 6(11), 271;

In Situ Observation of Crystal Rain and Its Effect on Columnar to Equiaxed Transition

State Key Laboratory of Advanced Special Steel, Shanghai Key Laboratory of Advanced Ferrometallurgy, School of Materials Science and Engineering, Shanghai University, Shanghai 200072, China
Shanghai Institute of Materials Genome, Shanghai 200444, China
Authors to whom correspondence should be addressed.
Academic Editor: Soran Birosca
Received: 30 August 2016 / Revised: 1 November 2016 / Accepted: 3 November 2016 / Published: 8 November 2016
(This article belongs to the Special Issue Process-Structure-Property Relationships in Metals)
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The investigation of a columnar to equiaxed transition (CET) and grain refinement is of high commercial importance for the improvement of the solidification structure of metal castings. The crystal rain from the free surface is frequently generated to produce grain refinement and promote a CET in alloys under the application of electromagnetic fields. However, the mechanism underlying the CET influenced by the generated crystal rain is not clear because the employed metallic alloys are opaque. In the present paper, the crystal rain in a transparent NH4Cl–H2O solution is produced by blowing a cooled nitrogen gas on the free surface to observe in situ its impact on the occurrence of a CET. The results show that the crystal rain can significantly promote a CET even in a high temperature gradient and that a CET only can occur when the temperature gradient is almost close to zero in the reference experiment. Finally, the most likely mechanism is discussed and clarified. View Full-Text
Keywords: NH4Cl–H2O; crystal rain; CET; refinement; physical simulation NH4Cl–H2O; crystal rain; CET; refinement; physical simulation

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Zhong, H.; Zhang, Y.; Chen, X.; Wu, C.; Wei, Z.; Zhai, Q. In Situ Observation of Crystal Rain and Its Effect on Columnar to Equiaxed Transition. Metals 2016, 6, 271.

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