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The substrate of as-cast Ni-28 wt% Sn hypoeutectic alloy immersed in liquid nitrogen is rapidly remolten and solidified by laser surface remelting with a scanning velocity of 10 mm/s and the laser power of 1950 W. The microstructure of the substrate and its effect on the microstructure of the molten pool are investigated by scanning electron microscope carefully. It is found that the substrate of the Ni-28 wt%Sn ingot is composed of coarse primary α-Ni dendrites and the interdendritic (α-Ni+Ni3Sn) eutectic. The growth orientations of α-Ni dendrites and the interdendritic eutectic are distributed nearly randomly in the as-cast substrate. There are three kinds of microstructure characterstic zones from the top to the bottom of melted pool. The growth directions of α-Ni dendrites with the primary dendritic spacings ranging from 4.19 to 6.91 μm are approximately parallel to the laser scanning direction at the top of the molten pool due to the fact that the temperature gradient at the interface between the molten pool and substrate tends to be parallel to the laser scanning direction. In the middle of the molten pool, the epitaxial α-Ni columnar dendrites are found to be inclined to grow in the direction vertical to the bottom of the molten pool due to the fact that the temperature gradients in most zones of the molten pool are perpendicular to the bottom of the molten pool. The formation of new primary dendrites by the growth of the tertiary arm results in the decrease of primary dendritic spacing in comparison with that at the bottom of the molten pool. There are a small quantity of residual α-Ni primary phase and a large amount of (α-Ni+Ni3Sn) eutectic at the bottom of the molten pool. The microstructure of laser remolten zone is greatly influenced by the substrate microstructure, and the growth direction of the α-Ni dendrite in the molten pool is also affected remarkably by both the heat flux and the preferred crystal orientations for dendritic growth. Compared with the mixed lamella, rod and divorced (α-Ni+Ni3Sn) eutectic microstructures in the substrate, the eutectic structure in the molten pool is completely composed of the refined lamellar eutectic, which grows epitaxially in the direction perpendicular to the interface between the molten pool and the substrate at the bottom of molten pool. The eutectic lamellar spacing increases from the top (0.23 μm± 0.01 μm) to the bottom (0.42 μm± 0.02 μm) of the molten pool due to the interface growth velocity decreasing from the top to the bottom. The Kurz-Giovanola-Trivedi model for rapid dendritic growth and the Trivedi-Magnin-Kurz model for eutectic growth are used to estimate the growth undercooling of the microstructure in the molten pool respectively. It is found that the growth undercooling of dendrites and the eutectic in the molten pool should be between 50.4 K and 112.5 K, which is much larger than the critical undercooling for anomalous eutectic growth found in the high undercooled solidification in the previous researches. This phenomenon means that the critical undercooling for anomalous eutectic growth reported in the previous literature may be not the sufficient condition for generating the anomalous eutectic.
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Keywords:
- rapid solidification /
- turned dendrite /
- Ni-Sn eutectic /
- undercooling
[1] Clpoet C R, Cochrane R F, Mullis A M 2013 Appl. Phys. Lett. 102 031906
[2] Zhao S, Li J F, Liu L, Zhou Y H 2009 Chin. Phys. B 18 1917
[3] Sobolev S L 2014 Phys. Lett. A 378 475
[4] Cao C D 2006 Chin. Phys. B 15 872
[5] Steen W M, Mazumder J 2010 Laser Material Processing (4th Ed.) (London: Springer-Verlag) p310
[6] Wang N 2008 Chin. Phys. Lett. 25 4168
[7] Kattamis T Z, Flemings M C 1970 Metall. Trans. 1 1449
[8] Piccone T J, Wu Y, Shiohara Y, Flemings M C 1987 Metall. Trans. A 18 925
[9] Wu Y, Piccone T J, Shiohara Y, Flemings M C 1988 Metall. Trans. A 19 1109
[10] Wei B B, Yang G C, Zhou Y H 1991 Acta Metall. Mater. 39 1249
[11] Li M J, Nagashiio K, Ishikawa T, Yoda S, Kuribayashi K 2005 Acta Mater. 53 731
[12] Trivedi R, Magnin P, Kurz W 1987 Acta Metall. 35 971
[13] Li J F, Jie W Q, Zhao S, Zhou Y H 2007 Metall. Mater. Trans. A 38 1806
[14] Li J F, Li X L, Liu L, Lu S Y 2008 J. Mater. Res. 23 2139
[15] Yang C, Gao J, Zhang Y K, Kolbe M, Herlach D M 2011 Acta Mater. 59 3915
[16] Geng D L, Xie W J, Wei B 2012 Appl. Phys. A 109 239
[17] Kurz W, Fisher D J 1992 Fundamentals of Solidification (3rd Ed.) (Switzerland: Trans Tech Publications) p83
[18] Trivedi R, Kurz W 1994 Acta Metall. Mater. 42 15
[19] Rappaz M, David S A, Vitek J M, Boatner L A 1989 Metall. Mater. Trans. A 20 1125
[20] Shi Y F, Xu Q Y, Gong M, Liu B C 2011 Acta Metall. Sin. 47 620 (in Chinese) [石玉峰, 许庆彦, 龚铭, 柳百成 2011 金属学报 47 620]
[21] Flemings M C (translated by Guan Y L) 1981 Solidification Processing (Beijing: Metallurgical Industry Press) p154 (in Chinese) [弗莱明斯 M C著, 关玉龙 译 1981 凝固过程 (北京: 冶金工业出版社)第154页
[22] Lin X, Yue T M, Yang H O, Huang W D 2006 Acta Mater. 54 1901
[23] Jackson K A, Hunt J D 1966 TMS-AIME 236 1129
[24] Trivedi R, Mason J T, Verhoeren J D, Kurz W 1991 Metall. Trans. A 22 2523
[25] Tiller W A 1958 Liquid Metals and Solidification (Cleveland: ASM) pp276-279
[26] Yang Y J, Wang J C, Zhang Y X, Zhu Y C, Yang G C 2009 Acta Phys. Sin. 58 650 (in Chinese) [杨玉娟, 王锦程, 张玉祥, 朱耀产, 杨根仓 2009 物理学报 58 650]
[27] Zhao P, Li S M, Fu H Z 2012 Acta Metall. Sin. 48 33 (in Chinese) [赵朋, 李双明, 傅恒志 2012 金属学报 48 33]
[28] Wang L, Wang N, Ji L, Yao W J 2013 Acta Phys. Sin. 62 216801 (in Chinese) [王雷, 王楠, 冀林, 姚文静 2013 物理学报 62 216801]
[29] Kurz W, Giovanola B, Trivedi R 1986 Acta Metall. 34 823
[30] Brandes E A 1983 Smithells Metals Reference Book (6th Ed.) (Bodmin, Cornwall: Butterworth & Co. Ltd) pp41-43
[31] Gaumann M, Bezencqn C, Canalis P, Kurz W 2001 Acta Mater. 49 1051
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[1] Clpoet C R, Cochrane R F, Mullis A M 2013 Appl. Phys. Lett. 102 031906
[2] Zhao S, Li J F, Liu L, Zhou Y H 2009 Chin. Phys. B 18 1917
[3] Sobolev S L 2014 Phys. Lett. A 378 475
[4] Cao C D 2006 Chin. Phys. B 15 872
[5] Steen W M, Mazumder J 2010 Laser Material Processing (4th Ed.) (London: Springer-Verlag) p310
[6] Wang N 2008 Chin. Phys. Lett. 25 4168
[7] Kattamis T Z, Flemings M C 1970 Metall. Trans. 1 1449
[8] Piccone T J, Wu Y, Shiohara Y, Flemings M C 1987 Metall. Trans. A 18 925
[9] Wu Y, Piccone T J, Shiohara Y, Flemings M C 1988 Metall. Trans. A 19 1109
[10] Wei B B, Yang G C, Zhou Y H 1991 Acta Metall. Mater. 39 1249
[11] Li M J, Nagashiio K, Ishikawa T, Yoda S, Kuribayashi K 2005 Acta Mater. 53 731
[12] Trivedi R, Magnin P, Kurz W 1987 Acta Metall. 35 971
[13] Li J F, Jie W Q, Zhao S, Zhou Y H 2007 Metall. Mater. Trans. A 38 1806
[14] Li J F, Li X L, Liu L, Lu S Y 2008 J. Mater. Res. 23 2139
[15] Yang C, Gao J, Zhang Y K, Kolbe M, Herlach D M 2011 Acta Mater. 59 3915
[16] Geng D L, Xie W J, Wei B 2012 Appl. Phys. A 109 239
[17] Kurz W, Fisher D J 1992 Fundamentals of Solidification (3rd Ed.) (Switzerland: Trans Tech Publications) p83
[18] Trivedi R, Kurz W 1994 Acta Metall. Mater. 42 15
[19] Rappaz M, David S A, Vitek J M, Boatner L A 1989 Metall. Mater. Trans. A 20 1125
[20] Shi Y F, Xu Q Y, Gong M, Liu B C 2011 Acta Metall. Sin. 47 620 (in Chinese) [石玉峰, 许庆彦, 龚铭, 柳百成 2011 金属学报 47 620]
[21] Flemings M C (translated by Guan Y L) 1981 Solidification Processing (Beijing: Metallurgical Industry Press) p154 (in Chinese) [弗莱明斯 M C著, 关玉龙 译 1981 凝固过程 (北京: 冶金工业出版社)第154页
[22] Lin X, Yue T M, Yang H O, Huang W D 2006 Acta Mater. 54 1901
[23] Jackson K A, Hunt J D 1966 TMS-AIME 236 1129
[24] Trivedi R, Mason J T, Verhoeren J D, Kurz W 1991 Metall. Trans. A 22 2523
[25] Tiller W A 1958 Liquid Metals and Solidification (Cleveland: ASM) pp276-279
[26] Yang Y J, Wang J C, Zhang Y X, Zhu Y C, Yang G C 2009 Acta Phys. Sin. 58 650 (in Chinese) [杨玉娟, 王锦程, 张玉祥, 朱耀产, 杨根仓 2009 物理学报 58 650]
[27] Zhao P, Li S M, Fu H Z 2012 Acta Metall. Sin. 48 33 (in Chinese) [赵朋, 李双明, 傅恒志 2012 金属学报 48 33]
[28] Wang L, Wang N, Ji L, Yao W J 2013 Acta Phys. Sin. 62 216801 (in Chinese) [王雷, 王楠, 冀林, 姚文静 2013 物理学报 62 216801]
[29] Kurz W, Giovanola B, Trivedi R 1986 Acta Metall. 34 823
[30] Brandes E A 1983 Smithells Metals Reference Book (6th Ed.) (Bodmin, Cornwall: Butterworth & Co. Ltd) pp41-43
[31] Gaumann M, Bezencqn C, Canalis P, Kurz W 2001 Acta Mater. 49 1051
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