电弧熔炼态Laves相Cr₂Nb/Cr合金的微观组织演变

来源期刊：金属学报2011年第6期

论文作者：李克伟 李双明 傅恒志

文章页码：663 - 670

关键词：真空非自耗电弧熔炼； Laves相Cr₂Nb； 离异共晶； 共晶领先相

Key words：vacuum non-consumable arc melting； Laves phase Cr₂Nb； divorced eutectic； eutectic leading phase

摘    要：采用真空非自耗电弧熔炼法制备了Cr-12%Nb(原子分数,下同)和Cr-20%Nb 2种成分合金的纽扣锭,利用XRD,OM,SEM和EDS对电弧熔炼态纽扣锭不同位置的组织及其竞争生长进行了研究.结果表明:Cr-12%Nb合金纽扣锭底部为细小的离异共晶,中部和顶部则由粗大的初生Cr相和共晶组织(Cr₂Nb+Cr)组成.而Cr-20%Nb纽扣锭底部出现的是胞状层片共晶组织,层片间距为0.3μm,随着距纽扣锭底部距离的增加,冷却速率逐渐降低,凝固组织中相继出现Cr₂Nb板条枝晶和花瓣状Cr₂Nb枝晶.同时,基于TMK快速凝固共晶模型和BCT枝晶生长模型,通过计算并比较共晶组织和Laves相Cr₂Nb枝晶界面生长温度,借助最高界面生长温度判据,很好地解释了Cr-20%Nb合金凝固组织的演变及其形成原因.

Abstract: The Cr-12%Nb (atomic fraction)and Cr-20%Nb alloys prepared by vacuum nonconsumable arc melting were investigated to understand the microstructure evolution of the Laves phase Cr₂Nb/Cr alloys.The solidified microstructures including the phase formation and competitive growth were studied using OM,XRD as well as SEM with an EDS.The results showed that different microstructure morphologies were observed in the Cr-12%Nb and Cr-20%Nb alloys.For the Cr-12%Nb alloy divorced eutectics were grown at the bottom part of the ingot.Primary Cr dendrites and coupled eutectic (Cr₂Nb+Cr) appeared in the middle and upper part of the ingot.For the Cr-20%Nb alloy cellular eutectics of which the lamellar spacing was about 0.3μm were found at the bottom of the ingot.With the decrease in cooling rate in the middle and upper part of the ingot,plate primary Cr₂Nb dendrites and petal-like Cr₂Nb dendrites were developed.Besides,using the TMK model for rapid eutectic solidification and the BCT dendritic growth model,the interface growth temperatures between the coupled eutectic(Cr₂Nb+Cr)and primary Cr₂Nb phase were computed and compared with the experimental results.Based on the maximum interface growth temperature criteria,the appearance of multiple solidified microstructures of the Cr-20%Nb alloy could be explained successfully.