Abstract In situ X-radiography imaging during the isothermal solidification of a 200 µm thin Al-24 at.% Ge sample was performed to determine dendritic growth rates, liquid concentrations and projected solid fractions. The experimental data allowed to follow dendrite tip growth velocities with high accuracy all the way from the initial transient growth related decrease of velocity via the expected increase of velocity during free dendrite growth to its final decrease during neighbor interacted growth. Concentration profiles in front of individual dendrite tips were measured to analyze the increase in far-field solute concentration due to solute accumulation. By time-resolved imaging of almost the entire 12 mm diameter sample, the global melt concentration could be derived. This enabled to estimate the initial nucleation undercooling of this un-refined alloy, which was so far unresolved. The experimental results are compared to a three-dimensional dendrite needle network model that simulates the experimental conditions, such as hexagonal dendrite structures and confined sample geometry. Although the simulation results are very sensitive to variations of the parameters undercooling and dendrite selection constant, one model parameter set is found that reproduces all experimentally measured solidification characteristics. The thorough experiment-model comparison indicates that the dendritic growth rates in this experimental configuration can be lower by a factor of 7 depending on undercooling than in the non-confined case.

中文翻译：

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等轴枝晶 Al-Ge 合金样品凝固特性的原位 X 射线照相和 DNN 模型对比研究

摘要 在等温凝固 200 µm 薄 Al-24 at.% Ge 样品期间进行原位 X 射线成像，以确定枝晶生长速率、液体浓度和投射的固体分数。实验数据允许以高精度跟踪枝晶尖端生长速度，从初始瞬态生长相关的速度降低到自由枝晶生长过程中速度的预期增加，再到相邻相互作用生长过程中的最终速度降低。测量单个枝晶尖端前面的浓度分布，以分析由于溶质积累导致的远场溶质浓度增加。通过对几乎整个 12 毫米直径样品的时间分辨成像，可以推导出整体熔体浓度。这使得能够估计这种未精炼合金的初始成核过冷，这是迄今为止尚未解决的问题。将实验结果与模拟六边形枝晶结构和受限样品几何形状等实验条件的三维枝晶针状网络模型进行比较。尽管模拟结果对参数过冷度和枝晶选择常数的变化非常敏感，但发现一个模型参数集可以再现所有实验测量的凝固特性。彻底的实验模型比较表明，与非受限情况相比，此实验配置中的枝晶生长速率可以根据过冷度降低 7 倍。将实验结果与模拟六边形枝晶结构和受限样品几何形状等实验条件的三维枝晶针状网络模型进行比较。尽管模拟结果对参数过冷度和枝晶选择常数的变化非常敏感，但发现一个模型参数集可以再现所有实验测量的凝固特性。彻底的实验模型比较表明，与非受限情况相比，此实验配置中的枝晶生长速率可以根据过冷度降低 7 倍。将实验结果与模拟六边形枝晶结构和受限样品几何形状等实验条件的三维枝晶针状网络模型进行比较。尽管模拟结果对参数过冷度和枝晶选择常数的变化非常敏感，但发现一个模型参数集可以再现所有实验测量的凝固特性。彻底的实验模型比较表明，与非受限情况相比，此实验配置中的枝晶生长速率可以根据过冷度降低 7 倍。尽管模拟结果对参数过冷度和枝晶选择常数的变化非常敏感，但发现一个模型参数集可以再现所有实验测量的凝固特性。彻底的实验模型比较表明，与非受限情况相比，此实验配置中的枝晶生长速率可以根据过冷度降低 7 倍。尽管模拟结果对参数过冷度和枝晶选择常数的变化非常敏感，但发现一个模型参数集可以再现所有实验测量的凝固特性。彻底的实验模型比较表明，与非受限情况相比，此实验配置中的枝晶生长速率可以根据过冷度降低 7 倍。