环境诱导的涂层-基体疲劳损伤行为及关键力学问题的研究

Plasma electrolytic oxidation (PEO) ceramic coating-substrate structure is as one of effective measures to improve the environmental fatigue and fracture in environmental engineering applications of most light metals such as aluminum alloys, magnesium alloys and titanium aluminum alloys. However, the failure behaviours including to environmental fatigue (coupling or uncoupling between environmental media and cyclic loadings) between light metals and ceramic coating-light metal substrate structure are whether to be alike? The critical mechanics parameters and their controlled issues in the failure models are significant for the engineering service of ceramic coating-substrate structure. In this work, the environment-induced fatigue damage models and mechanisms of ceramic coating-light metal substrates were carried out based on scanning electron microscope (SEM) in-situ observation technology, environmental fatigue testing system and other relative detecting methods of critical mechanics parameters including residual stress distribution in the coating layer and adhered strength both two interfaces. At the same time, the finite element (FE) analysis is to contribute to understand deeply the environmental fatigue damage mechanism of coating-substrate structure according to the experimental phenomena, especially in 3-dimensions of coating-substrate structure. Therefore, based on above mentioned the experiment methods and FE analysis, we can study on the reasonable range of ceramic coating thickness to have higher environmental fatigue strength or life, to regulate and control the residual stress distribution in the ceramic coating layer in order to effectively use the residual compression stress, to repair the surface and subsurface defects in order to decrease the stress concentration and electrochemistry action, to enhance the interface adhered strength in order to explore the reasonable hardness variation between the coating layer and substrate and effect of harder coating thickness on the softer substrate. These results indicated that processing mechanics parameters of ceramic coating-substrate structure in the converse design can be obtained based on the above mentioned critical mechanics parameters such as residual stress, stress concentration, interface adhered strength and hardness variation and environmental fatigue damage models etc. Therefore, an optimization coating-substrate structure with a high capacity of environmental fatigue and fracture has a safe engineering fatigue life.

微弧氧化陶瓷涂层-基体结构在材料工程应用中是提高其环境疲劳和环境断裂能力的有效措施之一，但是在环境、载荷耦合作用下的失效行为，特别是环境疲劳失效行为是否与材料的环境疲劳失效行为一致，失效模型中的关键力学参数及调控研究对于陶瓷涂层-轻金属基体材料环境下的安全服役十分重要。本研究拟通过SEM原位试验、环境疲劳试验及相关力学行为检测技术，对当前热门的陶瓷涂层-轻金属基体结构展开环境诱导下的各种疲劳损伤模型中的关键力学参数的定量表征和调控的实验与有限元分析相结合的研究。针对可能影响涂层-基体结构环境疲劳和环境断裂机制的各种关键力学问题，提出合理的涂层厚度范围、调控涂层残余应力分布、修复陶瓷涂层工艺缺陷、改善陶瓷涂层与不同轻金属界面结合强度，优化涂层-基体结构的环境疲劳强度和环境断裂韧性相关影响参数，为陶瓷涂层-基体结构的工程航空领域应用提供安全保障，为陶瓷涂层-基体结构环境疲劳延寿提供实验依据。

尽管铝合金具有较强的抗腐蚀能力，但环境对铝合金每年造成的腐蚀损害十分严重，特别是环境与疲劳载荷耦合作用下的事故也时有发生。因此，项目在提出了简便、可行地改善铝合金腐蚀疲劳性能对策-微弧氧化涂层基础上，深入研究硬质涂层与铝合金的疲劳损伤行为及关键力学问题的研究。.研究中借助先进的检测手段（如SEM、3D形貌（粗糙度）数字显微镜、XRD）等，多尺度的研究了涂层-基体结构材料的环境诱导下的疲劳损伤行为与特征，详细地分析了人工海水(3.0wt%NaCl、5.0wt.%NaCl)和外加载荷交互作用下的旋转弯曲疲劳实验结果。这些结果表明：相对腐蚀疲劳强度和应力强度因子作为关键力学参数能较好的表征或预测环境诱导的涂层-基体结构材料的高周（超高周）疲劳损伤行为和寿命估计；通过不同厚度的涂层（包括未涂层基体材料的比较）极化曲线和残余应力检测，定量揭示了腐蚀环境与外加载荷水平耦合作用临界循环次数范围及变化曲线；通过3D形貌疲劳断口分析方法，借助环境诱导的疲劳裂纹扩展面积与应力强度因子的数学关系建立了应力强度因子与疲劳循环寿命的线性表达式，为简单、快捷地预测环境疲劳寿命提供了有效的参考依据；此外，针对环境疲劳试验数据分散特性，提出了少量大样本得到的威布尔分布形状参数去预测大量的小样本疲劳数据方法，并且得到了可靠性验证。因此，该研究结果对可靠、低成本地预测材料疲劳寿命奠定了基础；对于不同涂层-基体结构材料的疲劳损伤曲线，得到了优化涂层-基体结构参数，为具有高腐蚀阻力的涂层-基体结构材料设计提供了有价值的参考依据。