冷却速率对Cu70Zr30 合金初生相及包晶转变的影响Effects of cooling rate on primary phase and peritectic transformation in Cu70Zr30 alloy

采用差热分析与阶梯铜模喷铸技术，研究不同冷却速率作用下Cu70Zr30 合金初生相尺寸、形貌以及包晶层厚度等的演化规律，讨论相选择与包晶转变的形成机理。结果表明：近平衡凝固条件下，差热分析试样中初生相形成与包晶转变的发生温度分别为1042 ℃和957 ℃，均滞后于平衡相图中相应的温度。由于包晶相两侧成分区间相差不大，且固态中原子扩散系数较小，因此，平均包晶层厚度仅为5 μm，并存在残余的Cu51Zr14 初生相。铜模喷铸条件下，非平衡凝固组织中初生相结构未发生改变，但包晶转变得到有效抑制。随冷却速率提高，过冷度的增加有利于形核发生，初生相形貌从定向束状向等轴晶发生转变。

The effects of cooling rate on the size and morphology of primary phase in Cu70Zr30 alloy,as well as the thickness of peritectic layer were investigated by differential thermal analysis and step copper mould spray casting techniques. The formation mechanisms of phase selection and peritectic transformation were discussed. The results show that the measured temperatures for primary phase and peritectic transformation are respectively 1042 ℃ and 957 ℃ in near-equilibrium solidification,which are smaller than the values from equilibrium phase diagram. Due to slight composition interval between the adjacent regions of peritectic phase and sluggish solute diffusion rate in solid,the average thickness of peritectic layer is merely 5 μm with the presence of residual primary phase Cu51Zr14. The structure of primary phase is not changed by copper mould spray casting,while peritectic transformation is suppressed effectively. With increasing cooling rate,undercooling is enhanced to activate more nucleation events,which generates the morphology transition of primary phase from directionally bundle to equiaxed-grain microstructure.

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