外加应力及含水蒸气环境中CoNiCrAlY涂层表面氧化层的生长机制研究

Dense oxide layer formed on the surface of CoNiClAl alloy coating doped by reactive elements (REs) could increase oxidation resistance properties of the components or thermal barrier coatings at high temperature under applied stress. With increasing of water vapor content in the combustion fuel, applied stress is becoming one of important factors to affect the oxidation behavior of CoNiCrAl coatings compared to that oxidized in dry air. Effect of reactive elements within the coatings on the oxidation behavior of CoNiCrAl alloy will be investigated during steam exposure at high temperature under complex applied stress (such as stress value, type and frequency) in this project...Effect of water vapor at high temperature on the thermodynamics and kinetics of CoNiCrAl alloy doped by REs, e.g. Y, Zr and Hf will be studied under applied stress. The detailed mechanism of influence of applied stress and water vapor on the defects within the alumina layer will be clearly analyzed. The phase transformation θ→α-Al2O3，especially the energy barrier during the above phase transformation, affected by REs and water vapor at the initially oxidation stage for the coatings under applied stress will be focused in this project. ..Another important research work in this project is how applied stress and water vapor affect the microstructure (grain orientation and size) of alumina layer and defects along alumina grain boundies as well as voids located at interface of the alumina/alloy coating. The detrimental oxides, e.g. spinel and others oxides nucleation and growth promoted by water vapor will also be studied through the measurement and calculation in order to suppress or hinder spinel formation...Residual stress concentration and cracks growth in the alumina oxide layer during the increasing and decreasing temperature stage within one cycling in humid air, especially under applied stress environment, will be the third research work in this project. The reason for the decreasing adhrence of alumina on the condition that the above new environment will be focused in this project. The mechanism about the effect of water vapor and applied stress on the defects (such as holes and cracks) within alumina on the CoNiCrAl alloy will be investigated in detail.

活性元素（如Y，Hf等）掺杂CoNiCrAl涂层高温生成致密氧化层，是结构部件或热障涂层抗氧化腐蚀的保证。高温燃气中水蒸气含量增加的同时，外加应力也成为影响CoNiCrAl涂层氧化行为的重要因素。为了理解新环境中涂层的抗氧化性能，本项目研究外加应力和含H2O气氛同时对CoNiCrAlY涂层氧化层生长行为的影响，主要内容包括：不同外加应力（集中应力或循环应力）和H2O对活性元素(如Y和Hf)掺杂CoNiCrAl涂层的动力学定量影响，以及对氧化铝晶界和界面缺陷生长的影响规律，氧化初期外加应力和水蒸气对θ→α-Al2O3相变过程中能垒大小的影响；外加应力和H2O对α-Al2O3的组织结构（晶粒取向和尺寸分布）交互影响，氧化过程中H2O和外加应力对涂层表面尖晶石和其它氧化物形核和生长的影响机制；明确新条件下氧化铝界面的弱化机理，明确H2O和外加应力对合金氧化膜宏观缺陷演化的影响。

外加应力（循环和应力集中）及含水气氛（高达82%）导致热障涂层中的粘结层发生快速氧化和脱落，严重制约热障涂层的使用寿命，危害部件的服役期限。.本项目结合涂层面临的新问题和挑战，围绕外加应力和水蒸气等条件下涂层表面氧化层生长行为和粘结性能为对象展开研究。.通过研究，本项目主要进一步理解高温氧化初期涂层表面θ(γ)→α-Al2O3的转化规律，发现外加应力对涂层表面氧化物生长的影响规律；获得不同涂层的氧化生长动力学，明确水蒸气对涂层表面α-Al2O3层的晶界缺陷形成和演化规律以及相应的界面弱化机理影响；获得调控氧化铝中氧化铪的分布位置等方法，可以抑制尖晶石生长，从而提高合金涂层的抗氧化性能，获得氧化物及应力集中等对涂层失效的影响；利用第一性原理计算，进一步理解Pt阻止H2O/OH-/H+对氧化铝和合金涂层界面结合强度的弱化机制，从而提高氧化铝的粘结性能；阐述涂层中孔隙率导致的应力集中和释放机制，陶瓷-金属过渡区对涂层裂纹生长方向具有重要影响，并分析了热处理对陶瓷涂层中的扩散和裂纹的影响。.在项目期间，参与国内会议2次，申请发明和授权实用专利各1项，发表期刊论文13篇（其中SCI论文5篇，EI论文3篇），会议论文3篇。随着上述问题的研究和理解，为涂层在外加应力水蒸气复杂环境中应用进一步奠定了理论基础，对促进热障涂层技术的普及和民用也具有重要现实意义。