铸态GH742合金的凝固特点及枝晶偏析

Solidification Characteristics and Dendritic Segregation of As-Cast GH742 Alloys

摘要:

高合金化GH742合金存在严重的枝晶偏析，Nb、Ti大量偏聚于枝晶间，导致MC碳化物、(γ+ γ′)共晶、Laves相、δ相等析出；高Mo含量及其枝晶间偏析是析出σ相的重要原因；La、Ce在枝晶间的富集促使含氧硫稀土相和Ni5Ce相的析出。与一般合金凝固特点不同，高含量Al、Ti、Nb导致GH742合金凝固过程中先后发生(γ+ γ′)和(γ+Laves)两种类型的共晶反应。结合差热分析技术和凝固组织特点确定了合金的凝固温度区间为1346-1190 ℃，凝固顺序为γ、MC、(γ+ γ′)、Laves、Ni5Ce。

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.