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采用落管方法实现了液态Cu-10 wt.% Zr亚共晶、Cu-12.27 wt.% Zr共晶和Cu-15 wt.% Zr过共晶合金在微重力无容器条件下的快速共晶与枝晶生长.Cu-12.27 wt.% Zr共晶合金的凝固组织随液滴直径减小由层片规则共晶向不规则共晶转变，且层片间距减小；Cu-10 wt.% Zr亚共晶合金的初生（Cu）相随液滴直径减小由粗大树枝晶向棒状晶转变，且所占体积分数增加，部分区域形成花状凝固组织，（Cu）相枝晶辐射向外生长；Cu-15 wt.% Zr过共晶合金初生相则为金属间化合物Cu9Zr2相，呈条状生长，随液滴直径减小冷却速率增大，凝固组织由宏观弯曲生长向球状晶胞转变.理论计算表明，三个合金液固相变枝晶与共晶的生长均由溶质扩散控制.测定Cu-10 wt.% Zr亚共晶合金初生（Cu）相显微硬度随液滴直径减小而增大，三个合金的共晶相随合金初始成分增大而增大.Eutectic phase transition involves the competitive nucleation and coupled growth of two solid phases within one liquid phase. Phase selection especially under unequilibrium condition, may result in novel microstructures and thus affects the performances of eutectic alloys. Liquid Cu-10 wt.% Zr hypoeutectic, Cu-12.27 wt.% Zr eutectic and Cu-15 wt.% Zr hypereutectic alloys are rapidly solidified in the containerless process in a 3 m drop tube. During the experiments, the Cu-Zr alloys are heated by induction heating in an ultrahigh vacuum chamber and further overheated to 200 K above their liquidus temperatures for a few seconds. Then the liquid alloys are ejected out from the small orifice and dispersed into tiny droplets after adding the argon gas flow. The solidified samples are analyzed by Phenom Pro scanning electron microscope and HXD-2000 TMC/LCD microhardness instrument. The competitive nucleation and growth among (Cu) dendrite, Cu9Zr2 dendrite and (Cu+Cu9Zr2) eutectic phase become more and more intensive as droplet diameter decreases. The layer spacing in Cu-12.27 wt.% Zr eutectic alloy decreases when the undercooling increases. And the microstructural transition takes place from lamellar eutectic to anomalous eutectic. The microstructure of Cu-10 wt.% Zr hypoeutectic alloy is characterized by (Cu) dendrite and lamellar eutectic. Whereas the microstructure in Cu-15 wt.% Zr hypereutectic alloy consists of Cu9Zr2 dendrite and lamellar eutectic. For the Cu-10 wt.% Zr hypoeutectic alloy, with the decrease of droplet size, the primary (Cu) phase transforms from coarse dendrites into equiaxed grains, and the volume fraction of (Cu) dendrite becomes larger and larger. As for Cu-15 wt.% Zr hypereutectic alloy, the primary Cu9Zr2 intermetallic compound grows in a band manner, and with the decrease of droplet size and increase of cooling rate, the solidified microstructure transforms from band Cu9Zr2 dendrite plus lamellar eutectic into spherical cell structure. The three alloys reach maximal undercooling at 177 K, 156 K and 204 K, respectively. The Trivedi-Magnin-Kurz and Lipton-Kurz-Trivedi/Boetinger-Coriell-Trivedi models are used to analyze the dendritic and eutectic growth as a function of undercooling. Theoretical analysis indicates that both dendritic growth and eutectic growth are controlled by solute diffusion during liquid-solid phase transition. To further investigate the effects of cooling rate and undercooling on the mechanical properties of Cu-Zr eutectic alloys, the microhardness of each of different phases is determined. The microhardness of the primary (Cu) phase within Cu-10 wt.% Zr hypoeutectic alloy is strengthened with the increase of cooling rate. The microhardness of eutectic within the three alloys also increases with increasing the cooling rate and the initial alloy composition of the alloy.
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Keywords:
- rapid solidification /
- high undercooling /
- eutectic /
- microgravity
[1] Cao L G, Cochrane R F, Mullis A M 2014 J. Alloys Compd. 615 S599
[2] Clopet C R, Cochrane R F, Mullis A M 2013 Appl. Phys. Lett. 102 031906
[3] Cui C J, Zhang J, Xue T, Liu L, Fu H Z 2015 J. Mater. Sci. Technol. 31 280
[4] Hu L, Li L H, Yang S J, Wei B B 2015 Chem. Phys. Lett. 621 91
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[8] Zhao C C, Zuo X W, Wang E G, Niu R M, Han K 2016 Mater. Sci. Eng. A 652 296
[9] Zuo X W, Guo R, Zhao C C, Zhang L, Wang E G, Han K 2016 J. Alloys Compd. 676 46
[10] Erol M, Byk U 2016 Trans. Indian. Inst. Met. 69 961
[11] Ge L L, Liu R P, Li G, Ma M Z, Wang W K 2004 Mater. Sci. Eng. A 385 128
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[13] L P, Wang H P 2016 Sci. Rep. 6 22641
[14] Trivedi R, Magnin P, Kurz W 1987 Acta Metall. 35 971
[15] Lipton J, Kurz W, Trivedi R 1987 Acta Metall. 35 957
[16] Boetinger W J, Coriell S R, Trivedi R 1987 Proceedings of the Fourth Conference on Rapid Solidification Processing, Principles and Technologies Baton Rouge, USA, 1987 p13
[17] Zhou S H, Napolitano R E 2010 Acta Mater. 58 2186
[18] Wang Q, Wang L M, Ma M Z, Binder S, Volkmann T, Herlach D M, Wang J S, Xue Q G, Tian Y J, Liu R P 2011 Phys. Rev. B 83 014202
[19] Gegner J, Shuleshova O, Kobold R, Holland-Moritz D, Yang F, Hornfeck W, Bednarcik J, Herlach D M 2013 J. Alloys Compd. 576 232
[20] Gierlotka W, Zhang K C, Chang Y P 2011 J. Alloys Compd. 509 8313
[21] Han X J, Schober H R 2011 Phys. Rev. B 83 224201
[22] Wang N, Li C R, Du Z M, Wang F M, Zhang W J 2006 Calphad 30 461
[23] Yang F, Holland-Moritz D, Gegner J, Heintzmann P, Kargl F, Yuan C C, Simeoni G G, Meyer A 2014 Europhys. Lett. 107 46001
[24] Okamoto H 2008 J. Phase Equilibria. 29 204
[25] Levi C G, Mehrabian R 1982 Matall. Trans. A 13 221
[26] Lee E S, Ahn S 1994 Acta Metall. Mater. 42 3231
[27] Aziz M J 1982 J. Appl. Phys. 53 1158
[28] Gale W F, Totememier T C 2004 Smithells Metals Reference Book (8th Ed.) (Amsterdam: Elsevier Publishers Ltd) p8-1
[29] Guo H S, Guo X P 2011 Trans. Nonfermus Met. Soc. China 21 1283
[30] Erol M, Byk U, Volkmann T, Herlach D M 2013 J. Alloys Compd. 575 96
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[1] Cao L G, Cochrane R F, Mullis A M 2014 J. Alloys Compd. 615 S599
[2] Clopet C R, Cochrane R F, Mullis A M 2013 Appl. Phys. Lett. 102 031906
[3] Cui C J, Zhang J, Xue T, Liu L, Fu H Z 2015 J. Mater. Sci. Technol. 31 280
[4] Hu L, Li L H, Yang S J, Wei B B 2015 Chem. Phys. Lett. 621 91
[5] Wu M W, Xiong S M 2011 Acta Phys. Sin. 60 058103 (in Chinese) [吴孟武, 熊守美 2011 60 058103]
[6] Yan N, Wang W L, Dai F P, Wei B B 2011 Acta Phys. Sin. 60 034602 (in Chinese) [闫娜, 王伟丽, 代富平, 魏炳波 2011 60 034602]
[7] Zhang N N, Luo X H, Feng S B, Ren Y H 2014 J. Mater. Sci. Technol. 30 499
[8] Zhao C C, Zuo X W, Wang E G, Niu R M, Han K 2016 Mater. Sci. Eng. A 652 296
[9] Zuo X W, Guo R, Zhao C C, Zhang L, Wang E G, Han K 2016 J. Alloys Compd. 676 46
[10] Erol M, Byk U 2016 Trans. Indian. Inst. Met. 69 961
[11] Ge L L, Liu R P, Li G, Ma M Z, Wang W K 2004 Mater. Sci. Eng. A 385 128
[12] Yang S J, Wang W L, Wei B B 2015 Acta Phys. Sin. 64 056401 (in Chinese) [杨尚京, 王伟丽, 魏炳波 2015 64 056401]
[13] L P, Wang H P 2016 Sci. Rep. 6 22641
[14] Trivedi R, Magnin P, Kurz W 1987 Acta Metall. 35 971
[15] Lipton J, Kurz W, Trivedi R 1987 Acta Metall. 35 957
[16] Boetinger W J, Coriell S R, Trivedi R 1987 Proceedings of the Fourth Conference on Rapid Solidification Processing, Principles and Technologies Baton Rouge, USA, 1987 p13
[17] Zhou S H, Napolitano R E 2010 Acta Mater. 58 2186
[18] Wang Q, Wang L M, Ma M Z, Binder S, Volkmann T, Herlach D M, Wang J S, Xue Q G, Tian Y J, Liu R P 2011 Phys. Rev. B 83 014202
[19] Gegner J, Shuleshova O, Kobold R, Holland-Moritz D, Yang F, Hornfeck W, Bednarcik J, Herlach D M 2013 J. Alloys Compd. 576 232
[20] Gierlotka W, Zhang K C, Chang Y P 2011 J. Alloys Compd. 509 8313
[21] Han X J, Schober H R 2011 Phys. Rev. B 83 224201
[22] Wang N, Li C R, Du Z M, Wang F M, Zhang W J 2006 Calphad 30 461
[23] Yang F, Holland-Moritz D, Gegner J, Heintzmann P, Kargl F, Yuan C C, Simeoni G G, Meyer A 2014 Europhys. Lett. 107 46001
[24] Okamoto H 2008 J. Phase Equilibria. 29 204
[25] Levi C G, Mehrabian R 1982 Matall. Trans. A 13 221
[26] Lee E S, Ahn S 1994 Acta Metall. Mater. 42 3231
[27] Aziz M J 1982 J. Appl. Phys. 53 1158
[28] Gale W F, Totememier T C 2004 Smithells Metals Reference Book (8th Ed.) (Amsterdam: Elsevier Publishers Ltd) p8-1
[29] Guo H S, Guo X P 2011 Trans. Nonfermus Met. Soc. China 21 1283
[30] Erol M, Byk U, Volkmann T, Herlach D M 2013 J. Alloys Compd. 575 96
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