Abstract: Carbide nucleation, growth and trapping behavior in directionally solidified MAR-M247 LC alloy and the corresponding mechanism have been investigated. Carbide forming element enrichment controls the carbide nucleation and the carbide growth behavior. If the carbide forming element enrichment and the nucleation sites are suitable, carbide nucleation can occur both above and below the liquidus temperature. Heterogeneous carbide nucleation is the preferred nucleation mechanism at low carbide forming element enrichment. Carbide growth occurs mainly at inter-secondary γ dendrite arm area and lower part of the mushy zone. The carbides are subsequently trapped at these positions after growing to a certain size. Some carbide is only partially trapped by the solid-liquid interface and the carbide growth accelerates after being partially trapped. A critical growth rate exists between 2×10-6 m/s and 5×10-6 m/s. The carbide volume fraction decreases in the directionally solidified art at slow growth rate that is caused by the lack of suitable growth site and the low trapping ability of the solid-liquid interface.

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