Revealing the nucleation and growth modes upon rapid solidification of undercooled Co-24 at.% Sn eutectic alloy by the crystallographic orientation relations

• Published in: Journal of alloys and compounds Vol. 1004; p. 175806
• Main Authors: Zhang, Fan, Zhang, Jianbao, Lü, Xinlei, Hua, Ke, Zhao, Yuhong, Wang, Haifeng
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 05.11.2024
• Subjects: Eutectic alloy; Growth; Nucleation; Orientation relation; Undercooling; Undercooling; Nucleation; Eutectic alloy; Growth; Orientation relation
• ISSN: 0925-8388
• DOI: 10.1016/j.jallcom.2024.175806

In the realm of undercooled eutectic alloys, the nucleation (i.e., copious vs. single) and the growth (i.e., coupled vs. decouple) modes, particularly the formation of anomalous eutectics, remain subjects of intense debate. This study delves into the crystallographic orientation relationships (ORs) during rapid solidification of an undercooled Co-24 at.% Sn eutectic alloy, where the high-temperature eutectic phases (β-Co3Sn2 and α-Co) persist to room temperature. A significant finding is the consistent observance of the same eutectic OR, i.e., 112̅0β−Co3Sn2 // 11̅1α−Co and 0001β−Co3Sn2 // 110α−Co, across various undercooling conditions from low to high and eutectic morphologies from lamellar to anomalous. This consistency underscores a unified growth mode of coupled eutectic growth. Furthermore, the observance of twin OR, i.e., 112̅1<11̅26>, 112̅2<1123̅> or 112̅4<2243̅>, between β-Co3Sn2 phases in diverse eutectic colonies, spanning from low to intermediate undercooling, and would also be the case of high undercooling, reinforces a single nucleation mode except under exceedingly low undercooling. Building on these insights, the anomalous eutectic colonies are suggested to be formed from a single origin where coupled eutectic growth of eutectic seaweeds or eutectic dendrites instead of dual origins. This study not only illuminates the underlying mechanisms of rapid solidification in undercooled eutectic alloys but also paves the way for innovative microstructure modulation strategies. [Display omitted] •The 112̅0β−Co3Sn2//11̅1α−Co, 0001β−Co3Sn2//110α−Co eutectic OR is followed independently with undercooling and microstructures.•Twin ORs are obeyed between β-Co3Sn2 in different eutectic colonies except for very low undercooling.•The single nucleation mode is the case if undercooling is not very low and the coupled eutectic growth mode is followed.•Anomalous eutectics are formed from coupled eutectic growth but not uncoupled dendrite growth.