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

背景/概述通过在燃气轮机热区经历的应力、应变和温度的循环变化来评估疲劳损伤的方法使用应力或应变的范围和在循环中达到的最高温度来根据疲劳曲线来预测损伤。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进行评估。最近的方法提出了包括塑性和蠕变分析的通用方法来确定松弛的应力和应变状态，并修正了疲劳损伤评估方法。在热截面构件的情况下，应力或应变可能与温度同步变化，或者可能存在相位差，其极端情况是与温度完全不同。这种情况发生在最高温度条件产生显著压应力的热点地区。在其他类型的循环中，由于外部热气体温度和内部冷却温度的边界条件以及由于旋转和气体负载力而产生的机械载荷，峰值应力或应变可能在上升或下降到峰值温度条件时发展，并对应于比峰值低得多的温度。这类组件确实具有热障涂层的额外好处，但到目前为止，几乎没有人了解这两种材料的力学行为是如何差异的。项目目的本项目的目的是通过对现有单晶材料数据的全面回顾，研究高温涂层系统中的热机械疲劳损伤，开发一个能代表真实使用行为的TMF寿命模型，包括在高应力和高温下发生的蠕变和氧化的影响，用有针对性的TMF试验验证该模型，并与有限元模型预测的应力场进行比较，研究TMF实验的断裂行为。这项工作可以研究损伤是如何在TMF循环范围内累积的，预测在这些条件下的第一个循环和稳定的循环响应。在循环过程中逐渐积累的损伤可能会让人对TMF的驾驶行为有一个了解。特别是，在逆时针135度循环中经历的损伤演化的整体知识是非常有意义的。研究还可以包括使用PD裂纹监测和数字图像相关(DIC)来高级表征TMF行为。可选择的材料将是带有铂和PtAl涂层系统的镍基单晶高温合金CMSX-3和CMSX-4。除了可以从公开文献中获得的数据之外，还可以参考劳斯莱斯的TMF测试数据。大纲计划1)熟悉关于单晶TMF的以前的工作、文献和疲劳数据，特别是涂层材料。2)开发TMF测试能力并建议验证测试。3)进行验证测试，包括断口图学研究。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.