Microstructural characteristics of Ni-Sb eutectic alloys under substantial undercooling and containerless solidification conditions
Microstructural characteristics of Ni-Sb eutectic alloys under substantial undercooling and containerless solidification conditions
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DOI：
10.1007/s11661-002-0223-1
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发表时间：
2002-04-01
影响因子：
2.8
通讯作者：
Wei, B
中科院分区：
文献类型：
--
作者：
Han, XJ;Wei, B
Ni-36 wt pct Sb 和 Ni-52.8 wt pct Sb 共晶合金均采用玻璃熔剂法和滴管技术进行高度过冷和快速凝固。 Ni-36% Sb 和 Ni-52.8% Sb 共晶合金的大块样品均过冷。使用玻璃熔剂方法，温度分别高达 225 K (0.16 T-E) 和 218 K (0.16 TE)。在临界过冷度 DeltaT(1)* 之外，揭示了从层状共晶到反常共晶的转变，该转变在过冷度 DeltaT(2)* 时完成。对于 Ni-36 pct Sb，DeltaT(1)* 近似于 60 K，DeltaT(2)* 近似于 218 K；对于Ni-52.8 pct Sb，DeltaT(1)*约为40 K，DeltaT(2)*约为139 K。在落管无容器凝固条件下，这两种共晶合金的共晶组织也表现出这种“层状共晶-异常共晶”形貌转变。同时，在落管技术加工的Ni-36%Sb共晶合金中发现了一种球形异常共晶晶粒，这归因于自由落体过程中重力减小条件导致的温度场和浓度场具有良好的空间对称性。在 Ni-52.8 pct Sb 共晶合金的快速凝固过程中，即使过冷度相对较大，表面成核也主导成核事件。基于当前共晶生长和枝晶生长模型的理论计算表明，在这两种共晶合金中，在大过冷度下，γ-Ni5Sb2枝晶生长取代了共晶生长。两个共晶相独立成核的趋势及其协同枝晶生长是导致层状共晶-异常共晶微观结构转变的原因。
Both Ni-36 wt pct Sb and Ni-52.8 wt pct Sb eutectic alloys were highly undercooled and rapidly solidified with the glass-fluxing method and drop-tube technique. Bulk samples of Ni-36 pct Sb and Ni-52.8 pct Sb eutectic alloys were undercooled. by up to 225 K (0.16 T-E) and 218 K (0.16 TE), respectively, with the glass-fluxing method. A transition from lamellar eutectic to anomalous eutectic was revealed beyond a critical undercooling DeltaT(1)*, which was complete at an undercooling of DeltaT(2)*. For Ni-36 pct Sb, DeltaT(1)* approximate to 60 K and DeltaT(2)* approximate to 218 K; for Ni-52.8 pct Sb, DeltaT(1)* approximate to 40 K and DeltaT(2)* approximate to 139 K. Under a drop-tube containerless solidification condition, the eutectic microstructures of these two eutectic alloys also exhibit such a "lamellar eutectic-anomalous eutectic" morphology transition. Meanwhile, a kind, of spherical anomalous eutectic grain was found in a Ni-36 pct Sb eutectic alloy processed by the drop-tube technique, which was ascribed to the good spatial symmetry of the temperature field and concentration field caused by a reduced gravity condition during free fall. During the rapid solidification of a Ni-52.8 pct Sb eutectic alloy, surface nucleation dominates the nucleation event, even when the undercooling is relatively large. Theoretical calculations on the basis of the current eutectic growth and dendritic growth models reveal that gamma-Ni5Sb2 dendritic growth displaces eutectic growth at large undercoolings in these two eutectic alloys. The tendency of independent nucleation of the two eutectic phases and their cooperative dendrite growth are responsible for the lamellar eutectic-anomalous eutectic microstructural transition.