Nucleation and phase selection in undercooled Fe-Cr-Ni melts: Part II. Containerless solidification experiments
Nucleation and phase selection in undercooled Fe-Cr-Ni melts: Part II. Containerless solidification experiments
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过冷 Fe-Cr-Ni 熔体中的成核和相选择：第二部分。
DOI：
10.1007/s11661-997-0147-x
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发表时间：
1997
期刊：
影响因子：
--
通讯作者：
W. Löser
中科院分区：
文献类型：
--
作者：
T. Volkmann;D. Herlach;W. Löser
研究了不同成分的Fe-Cr-Ni合金过冷熔体的凝固行为，分析了δ-bcc（铁素体）和γ-fcc（奥氏体）相的竞争形成。无容器凝固实验、电磁悬浮熔炼和雾化颗粒落管实验表明，即使在δ为亚稳成分的情况下，δ（bcc）凝固在深过冷熔体中也是优选的。在不同过冷度水平的结晶过程中的吸热事件的时间分辨检测，使一个临界过冷度的确定过渡到亚稳bcc相凝固在平衡fcc型合金。作为凝固前熔体过冷度的函数，测量稳定相和亚稳相的生长速度，揭示了相选择受成核控制。作为合金成分和熔体过冷度的函数的凝固过程的相选择图来自两种类型的实验：淬火样品的X射线相分析和过冷熔体的吸热事件的原位观测。实验结果与亚稳相图的理论预测和改进的成核理论相吻合。特别是，亚稳δ相形成的趋势，在一个广泛的组成范围内得到证实。
The solidification behavior of undercooled Fe-Cr-Ni melts of different compositions is investigated with respect to the competitive formation of δ-bcc (ferrite) and γ-fcc phase (austenite). Containerless solidification experiments, electromagnetic levitation melting and drop tube experiments of atomized particles, show that δ (bcc) solidification is preferred in the highly undercooled melt even at compositions where δ is metastable. Time-resolved detection of the recalescence events during crystallization at different undercooling levels enable the determination of a critical undercooling for the transition to metastable bcc phase solidifcation in equilibrium fcc-type alloys. Measurements of the growth velocities of stable and metastable phases, as functions of melt undercooling prior to solidification, reveal that phase selection is controlled by nucleation. Phase selection diagrams for solidification processes as functions of alloy composition and melt undercooling are derived from two types of experiments: X-ray phase analysis of quenched samples and in situ observations of the recalescence events of undercooled melts. The experimental results fit well with the theoretical predictions of the metastable phase diagram and the improved nucleation theory presented in an earlier article. In particular, the tendency of metastable δ phase formation in a wide composition range is confirmed.