Thermodynamic investigations of the diffusion-based and oxidation-based depletion mechanisms in MCrAlY coatings

由于燃气轮机供应商之间广泛的经济竞争以及与替代能源的竞争，现代燃气轮机供应商在开发、制造和服务领域面临着不断加剧的成本压力。提高燃气轮机进口温度或延长部件的使用寿命是提高燃气轮机设施效率和盈利能力的常用方法。为了保护部件免受增加的氧化和腐蚀风险，涡轮热气体路径中的组件被屏蔽，例如使用MCrAlY （M= Ni和/或Co）覆盖涂层。使mccraly涂层适应现代燃气轮机设施日益多样化的运行条件是确保每个部件和涡轮机最大使用寿命的必要条件。直到今天，一般的加工路线仍然是在实验试错的基础上调整化学成分和性能。然而，这是一个耗费时间和成本的过程，因为每个潜在的系统都必须经过验证和现场测试。经验表明，现代热力学软件包可以通过计算系统相关状态变量和模拟扩散过程来预测材料和合金的性能和结构。但是，目前这些程序只能模拟固相和/或液相之间的扩散。由于氧和相关氧化物（如Al2O3、Cr2O3、Y2O3）的流动性数据库（在商业上）不可用，不可能直接考虑大气的影响。然而，扩散控制氧化皮的形成和生长，邻近表面接近耗尽，对涂层和整个部件的寿命至关重要。该研究项目致力于研究与IN738LC相结合的著名的γ / β MCrAlY覆盖涂层的回火相关的氧化和相互扩散过程。在此数据的基础上，建立一个模拟模型，并随后通过氧化试验、长期热处理（12000 h）、微观研究、EDX、XRD以及可用的文献数据进行验证。与以往的研究相比，应根据确定的寿命标准和模拟结果给出寿命预测。假设伽马/ β MCrAlY模拟模型成功验证，计划在可能的第四个资助年度将其应用于化学和微观结构不同的伽马/ γ prime MCrAlY覆盖系统。通过这样做，可以分析所开发模型的通用性、可靠性和适应性。

Already today modern gas turbine suppliers are confronted with a steadily intensifying cost pressure in the development, manufacturing and service areas due to extensive economic competition among themselves and with alternative energy sources. Increasing the inlet temperatures into the turbine or extending the service life of components are established methods to increase the efficiency and profitability of gas turbine facilities. In order to protect parts from increased risk of oxidation and corrosion components in the hot gas path of a turbine are shielded for example with MCrAlY (M= Ni and/or Co) overlay coatings. Adapting MCrAlY coatings onto the more and more versatile operation conditions of modern gas turbine facilities is a necessity to ensure maximum service life of each part and the turbine. Still today the general processing route is to adapt the chemical composition and properties on an experimental trial and error basis. This, however, is a time and cost consuming process, because every single potential system has to be validated and field tested later. Experience has shown that modern thermodynamic software packages are a powerful to predict properties and structure of materials and alloys through calculation of system related state variables and simulation of diffusion processes. At the present point in time these programs can only simulate diffusion between solid and/or liquid phases, though. A straightforward consideration of the atmospheric influence is not possible due to (commercial) unavailability of mobility databases for oxygen and relevant oxides (e.g. Al2O3, Cr2O3, Y2O3). The diffusion controlled formation and growth of an oxide scale with adjacent surface near depletion, however, is crucial for the lifetime of the coating and the whole part. The research project is dedicated to investigate the tempering related oxidation and interdiffusion processes for a well known gamma/beta MCrAlY overlay coating in conjunction with IN738LC. On the basis of this data, a simulation model shall be developed and subsequently validated through oxidation trails, long-term heat treatments (12000 h), microscopic investigations, EDX, XRD, as well as available literature data. Compared to previous studies a lifetime prediction shall be given based on identified lifetime criteria and simulation results. Presuming a successful validation of the gamma/beta MCrAlY simulation model, the application onto a chemical and microstructurally different gamma/gamm prime MCrAlY overlay system is planned in a potential fourth funding year. By doing so, the universality, reliability and adaptability of the developed model shall be analysed.