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利用金相显微镜、电子探针、能谱仪等分析了含钒元素(V)0.066%的718合金铸锭凝固组织,对其微观组织和析出相特征进行分析,研究其中易偏析铌元素(Nb)的分布状态及偏析规律。结果表明,V元素的微合金化使718合金铸锭枝晶组织得到细化,二次枝晶间距及Nb元素的偏析系数均有所降低;由于Nb元素主要分布在Laves相及碳化物中,通过对二者体积分数的定量表征,V元素的加入大大降低Laves相及碳化物的析出,体积分数降低;线扫描分析表明,距Laves相越远,Nb元素含量越低,而含V样品中,这种含量降低的趋势有所减缓。所有分析结果均表明,V元素的合金化改善了718合金中Nb元素的偏析状态,细化了枝晶组织,对降低718合金均匀化热处理难度、提高合金成分和组织均匀性有利。含V碳化物在凝固过程中成为异质形核点,减小了凝固形核的驱动力,使得二次枝晶间距变小,表现出更小的Laves相体积分数和较细的枝晶组织。
The microstructure and precipitation characteristics of 718 alloy ingot containing vanadium (V) 0.066% were analyzed by metallographic microscope, electron probe, energy dispersive spectrometer and so on. The effects of the segregation of niobium (Nb ) Distribution and segregation rules. The results showed that microalloying of V element reduced the dendrite structure of 718 alloy ingot and decreased the secondary dendrite spacing and the segregation coefficient of Nb element. Because Nb element was mainly distributed in Laves phase and carbide, Through the quantitative characterization of the volume fraction of the two phases, the addition of V element greatly reduces the precipitation of Laves phase and carbides, and the volume fraction decreases. The line scan analysis shows that the farther the Laves phase, the lower the Nb element content, , This trend of reducing the content has slowed down. All the analysis results show that the alloying of V element improves the segregation state of Nb in 718 alloy and the dendritic structure is refined, which is beneficial to reduce the difficulty of homogenization heat treatment of 718 alloy and improve the alloy composition and the homogeneity of the alloy. V-containing carbides become heterogeneous nucleation sites during solidification, reducing the driving force for solidification nucleation, resulting in smaller secondary dendrite spacing, smaller Laves phase volume fractions, and finer dendritic structures .