Residual stress development and stability of Cr2AlC MAX phase coatings under thermal loading

多年来，提高部件抗氧化性和耐磨性的表面涂层是技术状态。然而，在研究新的涂层材料方面存在持续的努力，其显示出最佳的保护，从而导致例如关于效率的过程的优化。Cr2 AlC属于MAX相，具有陶瓷和金属性能以及优异的抗氧化性。因此，该材料作为抗氧化和耐磨涂层具有很大的潜力。影响涂层特性和寿命的关键因素是残余应力。通过在部件表面选择性地产生残余应力，可以极大地延长使用寿命。另一方面，在热循环暴露期间由热膨胀系数的大差异引起的热诱导残余应力可能导致灾难性的涂层失效。到目前为止，还没有关于残余应力的稳定性的工作，因此，在升高以及高温下的Cr2 AlC涂层的性能的耐久性。然而，这个问题的知识是至关重要的应用程序的薄膜在热暴露。另外，由于Cr2 AlC的氧化导致的铝的选择性氧化以及残余应力发展和膜特性，关于碳化铬和氧化铝相形成的影响，还没有已知的结果。虽然大量的结构变化似乎影响它clearly.In目前的建议中的残余应力的发展和稳定性的研究在薄Cr2 AlC薄膜的沉积参数的依赖性，衬底，热处理和热机械处理，以及氧化，包括所有的过程相形成和转变进行。进行这些调查，以有助于在薄膜中的残余应力发展的理解，以及调查的能力Cr2 AlC涂层的抗氧化和耐磨涂层。在这个项目中，我们进行等温和热循环原位高温x射线衍射（xrd）测量结合非原位xrd分析涂层从长期处理的等温和热循环炉。由于氧化过程的复杂性，实验将在真空和氧化气氛中进行，以分离热影响和氧化影响。腐蚀实验应考虑残余应力和氧化相的影响，评价Cr_2AlC涂层在机械和/或热暴露下的抗腐蚀性能，并分析薄膜中残余应力的松弛过程和失效机理。因此，它允许在热和机械负载过程中进行广泛的评估。

Surface coatings to improve oxidation and wear resistance for components are state of technology since many years. However, a continuous effort in research of new coating material is present, which show an optimal protection and thus lead to an optimization of processes e.g. concerning the efficiency. Cr2AlC, belongs to MAX-phases which have ceramic and metallic properties as well as excellent oxidation resistance. Hence this material has great potential as oxidation and wear resistant coatings.A crucial impact factor on coating characteristics and lifetime are residual stresses. With a selective generation of residual stresses in the component's surface it is possible to extend lifetime in a great amount. On the other hand thermal induced residual stresses caused by large differences in thermal expansion coefficients during thermo-cyclic exposure may result in catastrophic coating failure. Up to now, there is no work published about the stability of residual stresses and therefore the durability of the properties of Cr2AlC coatings at elevated as well as high temperatures. However, the knowledge of this issue is crucial for the application of thin films at thermal exposure. Additional there are no results known about the influence of chromium carbide and alumina phase formation due to the selective oxidation of aluminum as a result of oxidation of Cr2AlC and the residual stress development and film characteristics. Although the great amount in structural changes seem to influence it clearly.In the present proposal the research of the residual stress development and stability in thin Cr2AlC films in dependency of the deposition parameters, the substrate, the thermal and thermomechanical treatment as well as the oxidation including all processes associated with phase formation and transformation is conducted. These investigations are performed to contribute to the understanding in residual stress development in thin films as well as to investigate the ability of Cr2AlC coatings as oxidation and wear resistance coatings. In this project we perform isotherm and thermocyclic in situ high temperature x-ray diffraction (xrd) measurements combined with ex situ xrd analysis of coatings from long term treatments in isotherm and thermocyclic furnaces. Due to the complex processes which occur during oxidation, the experiments will be done in vacuum and oxidation atmosphere, to separate the thermal influence from the impacts through oxidation. Erosion experiments should permit an evaluation of the resistance of Cr2AlC coatings under mechanical and/or thermal exposure, taking into account the influence of residual stresses and phase development through oxidation.The analysis of the relaxation processes of residual stresses in thin films as well as failure mechanism are carried out additionally. Therefore it allows a widespread evaluation of processes during thermal and mechanical load.