The Role of Fundamental Material Parameters for the Fluorine Effect in the Oxidation Protection of Titanium Aluminides
The Role of Fundamental Material Parameters for the Fluorine Effect in the Oxidation Protection of Titanium Aluminides
复制标题
氟效应的基本材料参数在钛铝化物氧化防护中的作用
DOI：
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发表时间：
2008
期刊：
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通讯作者：
M. Schütze
中科院分区：
文献类型：
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作者：
H. Zschau;M. Schütze
为了改善钛铝合金在750 ° C以上温度下抗氧化性不足的问题，氟效应提供了一种创新的方法。本文的重点是定义与宏观行为（抗氧化性）及其长期稳定性相关的氟效应的基本材料变量。
热力学模型预测的总氟量的分压的走廊内的TiAl的氟效应。为了实现氟效应，所需的F浓度[at. - %]用20keV的氟离子注入，注入能量在5e~（15）和5e~（17）Fcm-2之间。通过使用蒙特卡罗模拟代码T-DYN计算注入深度分布，并通过使用非破坏性PIGE技术（质子诱导伽马射线发射）进行实验验证。在800 ° C-1000 ° C下的氧化测试之后，确定2e17 F cm-2/20 keV的值作为最佳注入参数集。根据这些结果，最大氟浓度被确定为用于开始氧化铝形成的基本材料变量，所需的氟量为约40 - 45原子%。然而，该最大氟浓度显示出快速降低至小于5原子%的值。仅在氧化（900 ° C和1000 ° C）几小时之后，随后缓慢降低。因此，最大氟浓度Cmax（现在位于金属/氧化物界面处）被确定为长期稳定性的基本参数。一个指数衰减函数，包含约1原子%的常数项描述了等温和循环氧化（900 ° C，1000 ° C）的Cmax的时间行为。由于表面上的氧化铝氧化皮充当氟的扩散屏障，因此Cmax的稳定性受到F-扩散到金属中的强烈影响。根据F-深度分布，确定了在900 ° C下氟向TiAl中的扩散系数作为Cmax长期稳定性的基本参数，其值为1.56e-15cm 2/s。
To improve the insufficient oxidation resistance of Titanium Aluminides at temperatures above 750°C the fluorine effect offers an innovative way. The focus of this paper is to define the fundamental material variables for the fluorine effect related to the macroscopic behaviour (oxidation resistance) and its long time stability.
The thermodynamic model predicted the fluorine effect for the TiAl within a corridor of total fluorine amount in terms of partial pressures. To realize the fluorine effect the required F-concentration [in at.-%] within the near surface region had to be found. Using fluorine ion implantation several fluences within 5e15 and 5e17 F cm -2 were implanted with an energy of 20 keV. The implantation depth profiles were calculated by using the Monte Carlo simulation code T-DYN and verified experimentally by using the non-destructive PIGE - technique (Proton Induced Gamma-ray Emission). After oxidation tests at 800°C – 1000°C a value of 2e17 F cm-2 / 20 keV was determined as an optimal implantation parameter set. Following these results the maximal fluorine concentration was identified to be a fundamental material variable for starting the alumina formation with a required fluorine amount of about 40-45 at.-%. However this maximum fluorine concentration showed a rapid decrease to values less than 5 at.-% only after a few hours of oxidation (900°C and 1000°C) followed by a slow decrease. Therefore the maximum fluorine concentration Cmax – now located at the metal/oxide – interface – was identified to be a fundamental parameter for the long time stability. An exponential decay function containing a constant term of about 1 at.-% was found to describe the time behaviour of Cmax for isothermal and cyclic oxidation (900°C, 1000°C). Because the alumina scale on the surface acts as a diffusion barrier for fluorine, the stability of Cmax is strongly influenced by the F-diffusion into the metal. From the F-depth profiles the diffusion coefficient of fluorine into the TiAl at 900°C was determined as a fundamental parameter for the long-term stability of Cmax showing a value of 1.56e-15cm 2 /s.