Solidification Characteristics and Dendritic Segregation of As-Cast GH742 Alloys

Abstract:

High alloying GH742 alloys exhibit severe dendritic segregation with Nb and Ti intensively segregated to the interdendritic regions, leading to the precipitation of MC carbide, (γ+γ′) eutectic, Laves phase and δ phase. High content of Mo as well as its dendritic segregation is the significant reason for the precipitation of σ phase. Two phases containing rare earth elements, Ni5Ce phase and RE-O-S phase, are precipitated in the interdendritic regions due to the enrichment of La and Ce. Different from other superalloys, both eutectic reactions of (γ+γ′) and (γ+Laves) take place in sequence during the solidification process of GH742 alloys owing to the high contents of Al, Ti and Nb. The solidification temperature range of GH742 alloys is between 1346 and 1190 oC, and the solidification sequence is γ, MC, (γ+γ′), Laves and Ni5Ce, which is determined by differential thermal analysis and solidification microstructure characterization.

Key words:GH742; solidification; segregation; microstructure