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以揭示共晶系合金在不同过冷度下凝固时初生相的选择规律和凝固组织形成机理为目的, 用熔融玻璃净化和循环过热相结合的方法, 将Ni100-xPx(x=18, 19, 19.6, 20, 21, 原子百分比)合金过冷至平衡液相线以下不同的温度, 用高速红外测温仪记录了试样的凝固冷却曲线, 详尽分析了试样的凝固组织.结果表明, 过冷Ni-P合金快速凝固过程中析出的初生相为α-Ni/Ni3P耦合共晶时, 整个凝固过程中仅出现一次再辉, 在所形成的异常共晶组织中α-Ni颗粒大小分布均匀;而当某一共晶相优先析出时, 另外一相需要在残留液相中重新形核, 致使凝固过程中出现两次再辉, 相应形成颗粒相大小截然不同的两类异常共晶组织;据此绘制了Ni-P合金初生相为共生共晶的区域. Ni-P合金中α-Ni的生长动力学明显快于Ni3P, 使得在大过冷度下过共晶合金也以α-Ni作为初生相进行凝固.In order to gain an insight into the primary phase selection and solidification structure formation while undercooled eutectic alloys solidify, Ni100-xPx (x=18, 19, 19.6, 20, 21, atomic percent) alloy melts are undercooled to different temperatures below the equilibrium liquidus. The recalescence behavior associated with rapid solidification is monitored by a high-speed infrared pyrometer, and the solidification structure is analyzed systematically. When α-Ni/Ni3P regular eutectic forms as the primary phase during rapid solidification, single recalescence event takes place. In the resulting anomalous eutectic, fine granular grains of α-Ni are distributed uniformly in the Ni3P matrix. When the primary phase is one of the eutectic phases, however, there is a second recalescence event following the first one, resulting from nucleation of the other phase in the remaining liquid and the subsequent rapid eutectic growth. In this case, there are two types of granular grains whose sizes are significantly different from those in the anomalous eutectics. Finally, a coupled growth zone of eutectics is determined. At large undercoolings, α-Ni rather than Ni3P solidifies as the primary phase even in the Ni-P hyper-eutectic alloys due to its rapider growth kinetics.
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Keywords:
- undercooled/
- recalescence/
- anomalous eutectic/
- coupled zone
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