冷卻速率對Cu70Zr30 合金初生相及包晶轉變的影響Effects of cooling rate on primary phase and peritectic transformation in Cu70Zr30 alloy

采用差熱分析與階梯銅模噴鑄技術，研究不同冷卻速率作用下Cu70Zr30 合金初生相尺寸、形貌以及包晶層厚度等的演化規律，討論相選擇與包晶轉變的形成機理。結果表明：近平衡凝固條件下，差熱分析試樣中初生相形成與包晶轉變的發生溫度分別為1042 ℃和957 ℃，均滯后于平衡相圖中相應的溫度。由于包晶相兩側成分區間相差不大，且固態中原子擴散系數較小，因此，平均包晶層厚度僅為5 μm，并存在殘余的Cu51Zr14 初生相。銅模噴鑄條件下，非平衡凝固組織中初生相結構未發生改變，但包晶轉變得到有效抑制。隨冷卻速率提高，過冷度的增加有利于形核發生，初生相形貌從定向束狀向等軸晶發生轉變。

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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