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 in sample growth rates between 0.8 x 10(-6) and 15 x 10(-6) m s(-1). The results indicate that carbide growth rate, carbide forming element enrichment and surrounding solid geometry determine carbide morphology and carbide composition. The carbide forming element enrichment and interface energy control carbide nucleation. Heterogeneous carbide nucleation 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-dendrite arm positions and the mushy zone bottom which are rich in carbide forming elements. At fast sample growth rates, the solid-liquid interface can trap carbide nuclei in front of it. This trapping tends to occur at the inter-secondary gamma-dendrite arm region. (C) 1998 Elsevier Science S.A. All rights reserved.