落管中Fe-Mo-Si三元包共晶合金的快速凝固机制

Rapid Solidification Mechanism of Fe-Mo-Si Ternary Quasiperitectic Alloy in Drop Tube

采用落管无容器处理技术实现了Fe-27．5％Mo-20．5％Si三元包共晶合金的快速凝固，获得直径介于50～900μm的合金小球，对其凝固机制进行了探讨。理论计算出不同直径液滴在落管中自由下落时的冷却速率和过冷度，实验中获得的最大过冷度达339K（0．21TL）。EDS和SEM测试结果表明，初生相为FeSi，包共晶相为τ1（Fe5MoSi4）和R（Fe2MoSi2）相。当300pm〈D≤900μm时，凝固组织由残余初生相、包共晶相和三相共晶组成；当直径≤300μm时，三相共晶受到抑制。根据晶体生长形态与相图，提出了合金液滴在不同粒径下的两种凝固方式。

Rapid solidification of 50-900 μm diameter droplets of Fe-27.5% Mo-20.5% Si ternary quasiperitectic alloy was achieved in a 3 m drop tube, the solidification mechanism was analyzed. The cooling rates and undercoolir;gs of the samples with different diameters during free fall were calculated and the maximum undercooling is determined to be 339 K（0.21 TL）. The EDS and SEM measurements reveal that the primary phase is FeSi, and the quasiperitectic phases are τ1 （Fe5MoSi4） and R（Fe2MoSi2）. When droplets＇ diameters are in the range of 300-900 μm, the solidification microstructures are composed of remnant primary phase, quasiperitectic phases and ternary eutectic, whereas the ternary eutectic is suppressed when diameter is below 300 μm. Based on crystal growth morphology and the phase diagram, it is found that this alloy is solidified in two ways corresponding to different diameters.