The Growth Pattern of Co 3 Sn 2 in Directional Solidification of Co-Sn Hypereutectic Alloy Melts
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INTRODUCTION
DURING the solidification of alloy melts, latent heat of crystallization (fusion) is released and alloying elements are redistributed between the solid and the liquid across the interface. If the interface becomes unstable, it will inevitably evolve into highly complex patterns. Dendritic growth of crystals has been known for a long time and occurs widely in solidifying alloys.[1–7] Recently, seaweed growth was also observed in solidification.[8] Pocheau et al.[9] performed the directional solidification of succinonitrile-ethylene alloy and found that seaweed growth occurred when the preferred crystallographic direction was different from the imposed heat flow direction. Akamatsu et al.[10,11] directionally solidified CBr4-8 mol pct C2Cl6 alloy, whose effective interfacial energy anisotropy is weak. A transition from cellular growth to seaweed growth was observed with the increase of growth velocity. Such seaweed growth was also found in the directional solidification of succinonitrile added with 0.25 pct poly
J.L. KANG is with the School of Materials Science and Engineering, Lanzhou Jiaotong University, Lanzhou 730070, People’s Republic of China, and also with the State Key Laboratory of Metal Matrix Composites and Shanghai Key Laboratory of Materials Laser Processing and Modification, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, People’s Republic of China. J.F. LI is with the State Key Laboratory of Metal Matrix Composites and Shanghai Key Laboratory of Materials Laser Processing and Modification, School of Materials Science and Engineering, Shanghai Jiao Tong University. Contact e-mail: jfl[email protected] Manuscript Submitted May 11, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS A
ethylene oxide, 1.5 pct acetone, or 1.3 pct camphor.[12] Wang et al.[13,14] employed (100)[011] orientated planar front seeds in directional solidification and observed the seaweed growth in Al-4.5 wt pct Cu alloy. Amoorezaei et al.[15] investigated the microstructural evolution in the directional solidification of Mg-0.5 wt pct Al alloy using a phase-field model. Their results indicated that a higher thermal gradient and larger pulling velocity favor the seaweed microstructural formation. Also, by means of the phase-field method, Xing et al. revealed a transition between degenerated seaweeds and tilted dendrites existing in the directional solidification of Al-3 wt pct Cu alloy[16] and SCN-0.24 wt pct camphor model alloy.[17] Wang et al.[18] simulated the microstructural evolution in directional solidification of Mg-6 wt pct Gd alloy. They found that the crystal grew in a seaweed pattern when the misorientation angle between the preferred crystal direction and temperature gradient h0 = p/6, but as the misorientation angle decreased, especially when h0 = p/36, the dendrite grew faster with no obvious tip splitting observed. As for undercooled solidification, Mullis and co-workers[19–21] found that the crystal growth mode in Cu melt changed from dendrite to seaweed as the undercooling reache
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