深过冷液态Al-Ni合金中枝晶与共晶生长机理?

杨尚京; 王伟丽; 魏炳波

doi:10.7498/aps.64.056401

西北工业大学应用物理系,西安,710072

Growth mechanisms of dendrites and eutectics within underco oled liquid Al-Ni alloys

摘要: 在自由落体条件下实现了液态Al-4 wt.%Ni亚共晶、Al-5.69 wt.%Ni共晶和Al-8 wt.%Ni过共晶合金的深过冷与快速凝固.计算表明，(Al+Al3 Ni)规则纤维状共晶的共生区是4.8—15 wt.%Ni成分范围内不闭合区域，且强烈偏向Al3Ni相一侧.实验发现，随液滴直径的减小，合金熔体冷却速率和过冷度增大，(Al)和Al3Ni相枝晶与其共晶的竞争生长引发了Al-Ni共晶型合金微观组织演化.在快速凝固过程中， Al-4 wt.%Ni亚共晶合金发生完全溶质截留效应，从而形成亚稳单相固溶体.当过冷度超过58K时， Al-5.69 wt.%Ni 共晶合金呈现从纤维状共晶向初生(Al)枝晶为主的亚共晶组织演变.若过冷度连续增大， Al-8 wt.%Ni过共晶合金可以形成全部纤维状共晶组织，并且最终演变为粒状共晶.

关键词:

Abstract: Al-4 wt.%Ni (hypoeutectic), Al-5.69 wt.%Ni (eutectic) and Al-8 wt.%Ni (hypereutectic) liquid alloys are highly undercooled and rapidly solidified under free fall condition. Theoretical calculations indicate that the coupled zone of (Al+Al3Ni) fibrous eutectic is an unclosed region in the composition range from 4.8 to 15 wt.% Ni, which is strongly skewed towards the Al3Ni phase side. It is found that the cooling rate and undercooling of liquid alloys would increase as the droplet size decreases. Then the microstructural evolution of Al-Ni alloys will be induced by the competitive growth of (Al) dendrite, Al3Ni dendrite, and (Al+Al3Ni) eutectic. During the rapid solidification of Al-4 wt.%Ni hypoeutectic alloy, complete solute trapping effect occurs and then causes the formation of metastable segregationless (Al) solid solution phase. When the droplet undercooling exceeds 58 K, the structural morphology of Al-5.69 wt.%Ni eutectic alloy shows a transition from (Al+Al3Ni) fibrous eutectic to primary phase (Al)-dominated hypoeutectic structure. As the undercooling increases further, the fibrous eutectic becomes the unique microstructure of Al-8 wt.%Ni hypereutectic alloy, and finally evolves into a kind of granular eutectic.

深过冷液态Al-Ni合金中枝晶与共晶生长机理?

西北工业大学应用物理系,西安,710072

关键词:

Growth mechanisms of dendrites and eutectics within underco oled liquid Al-Ni alloys

西北工业大学应用物理系,西安,710072

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