MC CARBIDE FORMATION IN DIRECTIONALLY SOLIDIFIED MAR-M247 LC SUPERALLOY

MC-type carbide formation in MAR-M247 LC superalloy was systematically investigated using directional solidification and quenching methods i n sample growth rates between 0.8 x 10(-6) and 15 x 10(-6) m s(-1). Th e results indicate that carbide growth rate, carbide forming element e nrichment and surrounding solid geometry determine carbide morphology and carbide composition. The carbide forming element enrichment and in terface energy control carbide nucleation. Heterogeneous carbide nucle ation can occur above the alloy liquidus temperature. Carbide forming element enrichment and trapping behavior of the solid-liquid interface control carbide growth, which occurs at inter-secondary gamma-dendrit e arm positions and the mushy zone bottom which are rich in carbide fo rming elements. At fast sample growth rates, the solid-liquid interfac e can trap carbide nuclei in front of it. This trapping tends to occur at the inter-secondary gamma-dendrite arm region. (C) 1998 Elsevier S cience S.A. All rights reserved.