The Al–Fe–Si system was studied for an isothermal section at 800 °C in the Al-rich part and at 900 °C in the Fe-rich part, and for half a dozen vertical sections at 27, 35, 40, 50 and 60 at.% Fe and 5 at.% Al. Optical microscopy and powder X-ray diffraction (XRD) was used for initial sample characterization, and Electron Probe Microanalysis (EPMA) and Scanning Electron Microscopy (SEM) of the annealed samples was used to determine the exact phase compositions. Thermal reactions were studied by Differential Thermal Analysis (DTA). Our experimental results are generally in good agreement with the most recent phase diagram versions of the system Al–Fe–Si. A new ternary high-temperature phase τ12 (cF96, NiTi2-type) with the composition Al48Fe36Si16 was discovered and was structurally characterized by means of single-crystal and powder XRD. The variation of the lattice parameters of the triclinic phase τ1 with the composition Al2+xFe3Si3−x (−0.3 < x < 1.3) was studied in detail. For the binary phase FeSi2 only small solubility of Al was found in the low-temperature modification LT-FeSi2 (ζβ) but significant solubility in the high-temperature modification HT-FeSi2 (ζα) (8.5 at.% Al). It was found that the high-temperature modification of FeSi2 is stabilized down to much lower temperature in the ternary, confirming earlier literature suggestions on this issue. DTA results in four selected vertical sections were compared with calculated sections based on a recent CALPHAD assessment. The deviations of liquidus values are significant suggesting the need for improvement of the thermodynamic models.

中文翻译：

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Al-Fe-Si 体系中的相平衡和结构研究

研究了 Al-Fe-Si 系统在富铝部分 800 °C 和富铁部分 900 °C 的等温截面，以及 27、35、40、50 处的六个垂直截面和 60 at.% Fe 和 5 at.% Al。光学显微镜和粉末 X 射线衍射 (XRD) 用于初始样品表征，并且退火样品的电子探针微量分析 (EPMA) 和扫描电子显微镜 (SEM) 用于确定确切的相组成。通过差热分析(DTA)研究热反应。我们的实验结果通常与 Al-Fe-Si 系统的最新相图版本非常吻合。发现了一种新的三元高温相 τ12（cF96，NiTi2 型），其成分为 Al48Fe36Si16，并通过单晶和粉末 XRD 进行了结构表征。详细研究了三斜晶相 τ1 的晶格参数随 Al2+xFe3Si3-x (-0.3 < x < 1.3) 组成的变化。对于二元相 FeSi2，在低温改性 LT-FeSi2 (ζβ) 中发现 Al 的溶解度很小，但在高温改性 HT-FeSi2 (ζα)（8.5 at.% Al）中溶解度显着。发现 FeSi2 的高温改性在三元中稳定到低得多的温度，证实了早期关于这个问题的文献建议。四个选定垂直截面的 DTA 结果与基于最近的 CALPHAD 评估的计算截面进行了比较。液相线值的偏差很大，表明需要改进热力学模型。