Microstructure formation and columnar to equiaxed transition during cold crucible directional solidification of a high-Nb TiAl alloy
In order to study the factors of columnar to equiaxed transition (CET) of high-Nb TiAl alloys, Ti46Al7Nb0.4W0.6Cr0.1B alloy has been fabricated by cold crucible directional solidification (CCDS) technique under different pulling rate from 3.3 μm/s to 16.7 μm/s. The marco/micro-structure and phase co...
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| Format: | Article |
| Language: | English |
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Elsevier
2021-03-01
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| Series: | Journal of Materials Research and Technology |
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| Online Access: | http://www.sciencedirect.com/science/article/pii/S2238785421001848 |
| _version_ | 1818864385470234624 |
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| author | Xuesong Xu Hongsheng Ding Haitao Huang He Liang Ruirun Chen Jingjie Guo Hengzhi Fu |
| author_facet | Xuesong Xu Hongsheng Ding Haitao Huang He Liang Ruirun Chen Jingjie Guo Hengzhi Fu |
| author_sort | Xuesong Xu |
| collection | DOAJ |
| description | In order to study the factors of columnar to equiaxed transition (CET) of high-Nb TiAl alloys, Ti46Al7Nb0.4W0.6Cr0.1B alloy has been fabricated by cold crucible directional solidification (CCDS) technique under different pulling rate from 3.3 μm/s to 16.7 μm/s. The marco/micro-structure and phase composition near solid–liquid interface have been characterized. Results show that the CET of the high-Nb TiAl alloy occurs with the increase of the pulling rate at the constant temperature gradient. The microstructure of the columnar grain is composed of α2/γ lamellar matrix and a coupling structure of striped-like B2+γ phases. The lamellar colonies in a columnar grain possess the same orientation, while the arrangement direction between the striped-like B2 phase and growth direction is 0° or 45°. A solidification map for CCDS is established which predicts columnar or equiaxed morphology according to the growth rate (R) and temperature gradient (G). The dendrite morphology at the solid–liquid interface after quenching and the CET is controlled by the actual temperature gradient at the tip of the dendrite. Meanwhile, the increase of growth rate and the satisfaction of heterogeneous nucleation conditions are the main factors for CET. The decrease of actual temperature gradient caused by quenching or the increase of liquidus gradient caused by increasing growth rate can increase the maximum supercooling degree ΔTC. When it reached the supercooling degree ΔTN required to form a new nucleus, equiaxed grains will be produced. In addition, the boride in this alloy can act as a heterogeneous nucleation core to promote CET. |
| first_indexed | 2024-12-19T10:30:49Z |
| format | Article |
| id | doaj.art-b7f9cb60e04d46d5b6f19e57da5d3500 |
| institution | Directory Open Access Journal |
| issn | 2238-7854 |
| language | English |
| last_indexed | 2024-12-19T10:30:49Z |
| publishDate | 2021-03-01 |
| publisher | Elsevier |
| record_format | Article |
| series | Journal of Materials Research and Technology |
| spelling | doaj.art-b7f9cb60e04d46d5b6f19e57da5d35002022-12-21T20:25:46ZengElsevierJournal of Materials Research and Technology2238-78542021-03-011122212234Microstructure formation and columnar to equiaxed transition during cold crucible directional solidification of a high-Nb TiAl alloyXuesong Xu0Hongsheng Ding1Haitao Huang2He Liang3Ruirun Chen4Jingjie Guo5Hengzhi Fu6National Key Laboratory for Precision Hot Processing of Metals, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, ChinaCorresponding author; National Key Laboratory for Precision Hot Processing of Metals, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, ChinaNational Key Laboratory for Precision Hot Processing of Metals, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, ChinaNational Key Laboratory for Precision Hot Processing of Metals, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, ChinaNational Key Laboratory for Precision Hot Processing of Metals, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, ChinaNational Key Laboratory for Precision Hot Processing of Metals, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, ChinaNational Key Laboratory for Precision Hot Processing of Metals, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, ChinaIn order to study the factors of columnar to equiaxed transition (CET) of high-Nb TiAl alloys, Ti46Al7Nb0.4W0.6Cr0.1B alloy has been fabricated by cold crucible directional solidification (CCDS) technique under different pulling rate from 3.3 μm/s to 16.7 μm/s. The marco/micro-structure and phase composition near solid–liquid interface have been characterized. Results show that the CET of the high-Nb TiAl alloy occurs with the increase of the pulling rate at the constant temperature gradient. The microstructure of the columnar grain is composed of α2/γ lamellar matrix and a coupling structure of striped-like B2+γ phases. The lamellar colonies in a columnar grain possess the same orientation, while the arrangement direction between the striped-like B2 phase and growth direction is 0° or 45°. A solidification map for CCDS is established which predicts columnar or equiaxed morphology according to the growth rate (R) and temperature gradient (G). The dendrite morphology at the solid–liquid interface after quenching and the CET is controlled by the actual temperature gradient at the tip of the dendrite. Meanwhile, the increase of growth rate and the satisfaction of heterogeneous nucleation conditions are the main factors for CET. The decrease of actual temperature gradient caused by quenching or the increase of liquidus gradient caused by increasing growth rate can increase the maximum supercooling degree ΔTC. When it reached the supercooling degree ΔTN required to form a new nucleus, equiaxed grains will be produced. In addition, the boride in this alloy can act as a heterogeneous nucleation core to promote CET.http://www.sciencedirect.com/science/article/pii/S2238785421001848TiAl alloyDirectional solidificationColumnar-to-equiaxed transitionDendrite growthConstitutional supercooling |
| spellingShingle | Xuesong Xu Hongsheng Ding Haitao Huang He Liang Ruirun Chen Jingjie Guo Hengzhi Fu Microstructure formation and columnar to equiaxed transition during cold crucible directional solidification of a high-Nb TiAl alloy Journal of Materials Research and Technology TiAl alloy Directional solidification Columnar-to-equiaxed transition Dendrite growth Constitutional supercooling |
| title | Microstructure formation and columnar to equiaxed transition during cold crucible directional solidification of a high-Nb TiAl alloy |
| title_full | Microstructure formation and columnar to equiaxed transition during cold crucible directional solidification of a high-Nb TiAl alloy |
| title_fullStr | Microstructure formation and columnar to equiaxed transition during cold crucible directional solidification of a high-Nb TiAl alloy |
| title_full_unstemmed | Microstructure formation and columnar to equiaxed transition during cold crucible directional solidification of a high-Nb TiAl alloy |
| title_short | Microstructure formation and columnar to equiaxed transition during cold crucible directional solidification of a high-Nb TiAl alloy |
| title_sort | microstructure formation and columnar to equiaxed transition during cold crucible directional solidification of a high nb tial alloy |
| topic | TiAl alloy Directional solidification Columnar-to-equiaxed transition Dendrite growth Constitutional supercooling |
| url | http://www.sciencedirect.com/science/article/pii/S2238785421001848 |
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