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Two-step crystal growth mechanism during crystallization of an undercooled Ni(50)Al(50) alloy
Crystallization processes are always accompanied by the emergence of multiple intermediate states, of which the structures and transition dynamics are far from clarity, since it is difficult to experimentally observe the microscopic pathway. To insight the structural evolution and the crystallizatio...
Autores principales: | , , , , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
Nature Publishing Group
2016
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Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4971477/ https://www.ncbi.nlm.nih.gov/pubmed/27486073 http://dx.doi.org/10.1038/srep31062 |
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author | An, Simin Li, Jiahao Li, Yang Li, Shunning Wang, Qi Liu, Baixin |
author_facet | An, Simin Li, Jiahao Li, Yang Li, Shunning Wang, Qi Liu, Baixin |
author_sort | An, Simin |
collection | PubMed |
description | Crystallization processes are always accompanied by the emergence of multiple intermediate states, of which the structures and transition dynamics are far from clarity, since it is difficult to experimentally observe the microscopic pathway. To insight the structural evolution and the crystallization dynamics, we perform large-scale molecular dynamics simulations to investigate the time-dependent crystallization behavior of the NiAl intermetallic upon rapid solidification. The simulation results reveal that the crystallization process occurs via a two-step growth mechanism, involving the formation of initial non-equilibrium long range order (NLRO) regions and of the subsequent equilibrium long range order (ELRO) regions. The formation of the NLRO regions makes the grains rather inhomogeneous, while the rearrangement of the NLRO regions into the ELRO regions makes the grains more ordered and compact. This two-step growth mechanism is actually controlled by the evolution of the coordination polyhedra, which are characterized predominantly by the transformation from five-fold symmetry to four-fold and six-fold symmetry. From liquids to NLRO and further to ELRO, the five-fold symmetry of these polyhedra gradually fades, and finally vanishes when B2 structure is distributed throughout the grain bulk. The energy decrease along the pathway further implies the reliability of the proposed crystallization processes. |
format | Online Article Text |
id | pubmed-4971477 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2016 |
publisher | Nature Publishing Group |
record_format | MEDLINE/PubMed |
spelling | pubmed-49714772016-08-11 Two-step crystal growth mechanism during crystallization of an undercooled Ni(50)Al(50) alloy An, Simin Li, Jiahao Li, Yang Li, Shunning Wang, Qi Liu, Baixin Sci Rep Article Crystallization processes are always accompanied by the emergence of multiple intermediate states, of which the structures and transition dynamics are far from clarity, since it is difficult to experimentally observe the microscopic pathway. To insight the structural evolution and the crystallization dynamics, we perform large-scale molecular dynamics simulations to investigate the time-dependent crystallization behavior of the NiAl intermetallic upon rapid solidification. The simulation results reveal that the crystallization process occurs via a two-step growth mechanism, involving the formation of initial non-equilibrium long range order (NLRO) regions and of the subsequent equilibrium long range order (ELRO) regions. The formation of the NLRO regions makes the grains rather inhomogeneous, while the rearrangement of the NLRO regions into the ELRO regions makes the grains more ordered and compact. This two-step growth mechanism is actually controlled by the evolution of the coordination polyhedra, which are characterized predominantly by the transformation from five-fold symmetry to four-fold and six-fold symmetry. From liquids to NLRO and further to ELRO, the five-fold symmetry of these polyhedra gradually fades, and finally vanishes when B2 structure is distributed throughout the grain bulk. The energy decrease along the pathway further implies the reliability of the proposed crystallization processes. Nature Publishing Group 2016-08-03 /pmc/articles/PMC4971477/ /pubmed/27486073 http://dx.doi.org/10.1038/srep31062 Text en Copyright © 2016, The Author(s) http://creativecommons.org/licenses/by/4.0/ This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/ |
spellingShingle | Article An, Simin Li, Jiahao Li, Yang Li, Shunning Wang, Qi Liu, Baixin Two-step crystal growth mechanism during crystallization of an undercooled Ni(50)Al(50) alloy |
title | Two-step crystal growth mechanism during crystallization of an undercooled Ni(50)Al(50) alloy |
title_full | Two-step crystal growth mechanism during crystallization of an undercooled Ni(50)Al(50) alloy |
title_fullStr | Two-step crystal growth mechanism during crystallization of an undercooled Ni(50)Al(50) alloy |
title_full_unstemmed | Two-step crystal growth mechanism during crystallization of an undercooled Ni(50)Al(50) alloy |
title_short | Two-step crystal growth mechanism during crystallization of an undercooled Ni(50)Al(50) alloy |
title_sort | two-step crystal growth mechanism during crystallization of an undercooled ni(50)al(50) alloy |
topic | Article |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4971477/ https://www.ncbi.nlm.nih.gov/pubmed/27486073 http://dx.doi.org/10.1038/srep31062 |
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