(1. 西安理工大学 材料科学与工程学院， 西安 710048;
2. 西北工业大学 凝固技术国家重点实验室， 西安 710072;
3. 西安交通大学 机械工程学院， 西安 710049)
摘 要: 在高真空度下， 采用熔融玻璃净化与循环过热相结合的方法，在宽的过冷度范围内， 研究了Cu50Ni50合金凝固组织形态演化过程。结果表明， 随着过冷度增大， 凝固组织发生了3次转变。 其中， 当120 K(ΔT2*)<ΔT<192 K(ΔT3*)时， 凝固组织发生第2次转变，由粒状晶演变为定向生长的深过冷枝晶。 通过组织观察和过冷熔体枝晶生长过程的计算发现， 快速凝固形成的枝晶在再辉和再辉结束后枝晶熟化过程被高度抑制是在该过冷度区间形成定向枝晶的原因。
关键字: 深过冷； Cu50Ni50合金；枝晶熟化； 定向凝固
（1. College of Material Science and Technology， Xi′an University of Technology， Xi′an 710048, P.R.China;
2. State Key Laboratory of Solidification Processing， Northwestern Polytechnical University， Xi′an 710072, P.R.China;
3. School of Mechanical Engineering，Xi′an JiaoTong University， Xi′an 710049, P.R.China）
Abstract:The evolution of solidification microstructuresin undercooled Cu50Ni50 melts was systematically investigated， by using glass fluxing technique combinedwith cycle superheating in high vacuum. Within the achieved wide range of undercoolings， three consecutive microstructural transitionswith the increase of undercooling are revealed. When the melt undercooled into the range of 120 K(ΔT2* )<Δ T <192 K(ΔT3* )， the second transition of microstructure from the first refined granular grain to coarse grained dendritic microstructure takes place. And in this undercooling range， directional dendritic solidification can berealized. Based on the microstructure observation as well as calculations of the solid/liquid composition and undercooling using BCT model of the dendritic growth， it is found that the ripping and remelting processes of dendrites are restrained, which causes the formation of directional dendrites.
Key words: superundercooling； Cu50Ni50 alloys； dendritic ripping; directional solidification
