Mechanical characterisation of CMSX-3 and CMSX-4 with PT and PTAL Coatings under thermo-mechanical fatigue loading conditions

背景/综述用于评估燃气涡轮机热段中经历的应力、应变和温度的循环变化引起的疲劳损伤的方法使用应力或应变的范围以及循环中达到的最高温度，根据该范围和最高温度从疲劳曲线预测损伤。这导致了基于弹性预测的疲劳寿命，然后根据发动机寿命要求对其进行评估。最近的方法提出了塑性和蠕变分析的一般用途，包括确定松弛应力和应变状态与修订的疲劳损伤评估方法。在热截面部件的情况下，应力或应变可能随温度同相变化，或者可能有一个相位差，在其极端情况下将完全与温度异相。这种情况发生在最高温度条件产生显著压应力的热点中。在其它类型的循环中，由于外部热气体温度和内部冷却温度的边界条件与由于旋转和气体加载力引起的机械加载相结合而发生瞬态效应，峰值应力或应变可以在上升或下降到峰值温度条件时发展，并且将对应于比峰值低得多的温度。阻隔涂层，但到目前为止，很少有了解，真正捕捉如何在两种材料的机械行为的区别。项目目的本项目的目的是通过对单晶材料现有数据的全面审查，研究高温涂层系统的热机械疲劳损伤，以开发一个能够代表观察到的真实使用行为的寿命模型，包括在高应力和高温度下发生的蠕变和氧化的影响，通过有针对性的疲劳试验验证该模型，并将疲劳试验的断裂行为与有限元模型预测的应力场进行比较。这项工作可以研究在疲劳循环范围内损伤是如何累积的，预测在这些条件下的第一循环和稳定循环响应。围绕循环的损伤的增量累积可以产生对驾驶员驾驶行为的理解。特别是，在逆时针-135度循环中经历的损伤演变的整体知识是非常感兴趣的。研究还可以结合使用局部放电裂纹监测和数字图像相关（DIC），以进一步表征疲劳行为。所选材料将是镍基单晶高温合金CMSX-3和CMSX-4，带有Pt和PtAl涂层系统。除了公开文献中的数据外，还将参考罗尔斯-罗伊斯公司的疲劳试验数据。2）发展单晶体的抗拉强度试验能力，并提出验证试验建议。3）进行验证试验，包括断口分析研究。4）演示在发动机部件上的应用。

Background/OverviewThe approach for the assessment of fatigue damage from cyclic variation of stress, strain and temperature as experienced in the hot section of a gas turbine uses the range of stress or strain and the maximum temperature attained in the cycle against which to predict the damage from fatigue curves. This results in a fatigue life based on an elastic prediction which is then assessed against the engine life requirements. Recent methods have proposed the generic use of analyses with plasticity and creep included to determine the relaxed stress and strain state with a revised fatigue damage assessment approach.In the case of hot section components, the stress or strain may vary in-phase with the temperature, or there may be a phase difference which at its extreme would be completely out-of-phase with the temperature. This case occurs in a hotspot where the maximum temperature condition generates a significant compressive stress. In other types of cycle where transient effects occur due to the boundary conditions of the external hot gas temperature and the internal cooling temperature combined with the mechanical loading due to rotational and gas loading forces, the peak stress or strain may develop on the rise or fall to the peak temperature condition and would correspond to a much lower temperature than the peak.Such components do have the added benefit of thermal barrier coatings, but to date, little understanding is currently available that truly captures how the mechanical behaviour differentiates across the two materials. Project AimsThe aim of this project is to investigate thermo-mechanical fatigue damage in high temperature coated systems through a thorough review of existing data available on single crystal materials, to develop a TMF lifing model that can represent the true service behaviour observed including the influence of creep and oxidation that occurs at high stresses and temperatures, to validate this model with targeted TMF tests and to investigate the fracture behaviour of the TMF experiments in comparison with predicted stress fields from finite element models.The work could investigate how damage is accumulated in a range of TMF cycles, predicting the first cycle and stabilised cycle responses under these conditions. The incremental accumulation of damage around the cycle may generate an understanding of the driving behaviours in TMF. In particular, a holistic knowledge of the damage evolution experienced in a counter-clockwise -135 degree cycle is of great interest. Research could also incorporate the use of PD crack monitoring and Digital Image Correlation (DIC) for advanced characterisation of the TMF behaviour.The materials of choice would be the nickel based single crystal superalloys CMSX-3 and CMSX-4 with Pt and PtAl coating systems.TMF test data from Rolls-Royce would be referred to in addition to that available from open literature.Outline Plan1) Familiarisation with previous work, literature, and fatigue data on TMF in single crystals, with particular emphasis on coated materials.2) Develop TMF testing capability and propose validation tests.3) Perform validation tests including fractographic studies.4) Demonstrate application to an engine component.