铌在一种高合金化高温合金中的偏析与扩散行为

研究铌在一种高合金化镍基高温合金凝固过程中的偏析和均匀化过程中的扩散行为。铌严重偏析于枝晶间区域,其偏析系数高达4.30。许多富铌相,包括Laves相、δ相、（γ＋γ′）共晶、MC和M6C碳化物等在枝晶间析出。利用差热分析和在不同温度、时间的均匀化处理确定各种富铌相的溶解温度和枝晶偏析的消除程度。元素扩散计算表明：铌的扩散速率随着均匀化温度的提高而显著增加,从而有效地缩短均匀化时间。提出一种无初熔的三步均匀化制度,可以完全消除铌的枝晶偏析,获得均一的组织。

Segregation and diffusion behavior of niobium in a highly alloyed nickel-base superalloy

The segregation during solidification and high temperature diffusion during homogenization of niobium in a highly alloyed nickel-base superalloy were investigated. Niobium is seriously segregated into the interdendritic regions with segregation coefficient as high as 4.30. Various niobium-enriched phases including Laves phase, δ phase, (γ+γ′) eutectic, MC and M₆C types of carbides precipitated in the interdendritic regions. The soluble temperature of niobium-enriched phases and the degree of dendritic segregation were determined by differential thermal analysis and homogenization treatments at varied temperatures and times. The calculation of elemental diffusion indicates that the diffusion rate of niobium increases remarkably with the homogenization temperature increasing, so that the annealing time can be effectively reduced. A three-step homogenization treatment technology without incipient melting was established to eliminate the segregation of niobium and to obtain a uniform microstructure.