中文摘要：

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％Nb2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：Cr12％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O．3卢m，随着距纽扣锭底部距离的增加，冷却速率逐渐降低，凝固织中相继出现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CrzNb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．

英文摘要：

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 0.3 #m 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.