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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。
The diffusion behavior of niobium in segregation and homogenization during the solidification of a high alloyed nickel-base superalloy was investigated. Niobium segregates severely in the interdendritic region with a segregation coefficient up to 4.30. Many rich niobium phases, including Laves phase, δ phase, (γ + γ ’) eutectic, MC and M6C carbides and the like precipitate between dendrites. Differential thermal analysis and homogenization at different temperatures and times were used to determine the dissolution temperature and the degree of dendrite segregation of the niobium-rich phases. The elemental diffusion calculations show that the diffusion rate of niobium increases significantly with the increase of the homogenization temperature, which effectively shortens the homogenization time. A three-step homogenization without initial melting was proposed to completely eliminate the dendritic segregation of niobium and obtain uniform structure.