(Co76Sn24)(100-x)Nb-x (x = 0, 0.5, 0.8, 1.0) eutectic alloy melts were solidified at small undercooling for investigating the effect of Nb addition on microstructural development. With increasing Nb content, the solidification interface transits from eutectic seaweed (x = 0) to eutectic dendrite (x = 0.5) as a response to the change in the anisotropy of interfacial energy. Coupled eutectic growth can no longer be maintained within the main stems at x = 0.8 because the enrichment of Nb in the liquid ahead of the interface causes a significant difference in growth velocity between the alpha-Co and beta-Co3Sn2 phases and, as such, Co3Sn2 doublons form. For x = 1.0, the difference in growth kinetics between the two eutectic phases is so large that divorced eutectic growth takes place on a large scale. Letting the undercooling prior to solidification increase, the eutectic interface morphology of (Co76Sn24)(99.5)Nb-0.5 eutectic alloys returns from dendritic pattern back to factual seaweed pattern at more than 38 K undercooling and then transits to compact seaweed pattern at more than 181 K undercooling. The eutectic growth velocity slightly increases at low and intermediate undercooling but obviously decreases at large undercooling due with Nb addition. (C) 2016 Elsevier B.V. All rights reserved.
(Co76Sn24)(100-x)Nb-x (x = 0, 0.5, 0.8, 1.0) 共晶合
金在较小的过冷度下凝固,以研究
铌(Nb)添加对微观结构发展的影响。随着
铌含量的增加,凝固界面从共晶海带状(x = 0)转变为共晶树枝状(x = 0.5),这是由于界面能量各向异性变化所引起的响应。在x = 0.8时,液相中
铌的富集导致α-Co和β-
Co3Sn2两相生长速度出现显著差异,从而形成 双晶。对于x = 1.0的情况,由于两共晶相生长动力学差异巨大,导致大规模发生分离共晶生长。增大凝固前的过冷度,(Co76Sn24)(99.5)Nb-0.5共晶合
金的共晶界面形貌在超过38 K的过冷度时从树枝状恢复为事实上的海带状,并在超过181 K的过冷度时转变为紧致的海带状。由于添加
铌,共晶生长速度在低温和中温过冷条件下略有增加,但在高温过冷条件下显著降低。
© 2016 Elsevier B.V. 保留所有权利。