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

今天，现代燃气轮机供应商在开发、制造和服务领域已经面临着日益加剧的成本压力，这是因为它们之间以及与替代能源之间的广泛经济竞争。提高汽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既定方法。为了保护部件免受氧化和腐蚀风险的增加，涡轮机热气通道中的部件被保护起来，例如用MCrAlY(M=Ni和/或Co)覆盖涂层。将MCrAlY涂层应用于现代燃气轮机设备越来越多样化的运行条件，是保证各部件和透平最大使用寿命的需要。时至今日，通常的加工路线仍然是在试验性试验和错误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，因为每个单独的潜在系统都必须在以后进行验证和现场测试。经验表明，通过计算与系统有关的状态变量和模拟扩散过程，现代热力学软件包是预测材料和合金性能和结构的强大工具。然而，目前这些程序只能模拟固体和/或液体之间的扩散。由于(商业)无法获得氧和相关氧化物(例如，Al_2O_3、Cr2O_3、Y_2O_3)的迁移率数据库，因此不可能直接考虑大气影响。然而，扩散控制了邻近表面接近耗尽的氧化膜的形成和生长，这对涂层和整个零件的寿命至关重要。该研究项目致力于研究与IN738LC相结合的众所周知的伽马/贝塔MCrAlY覆层的回火相关氧化和互扩散过程。在此数据的基础上，应开发一个模拟模型，并随后通过氧化试验、长期热处理(12000 H)、微观研究、EDX、X射线衍射以及现有的文献数据进行验证。与以往的研究相比，应根据已识别的寿命准则和模拟结果进行寿命预测。假设伽马/贝塔MCrAlY模拟模型得到成功验证，计划在潜在的第四个供资年度将其应用于化学和微观结构不同的伽马/伽马优质MCrAlY覆盖系统。在此基础上，分析了模型的普适性、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.