基于小变形的热障涂层界面氧化力化耦合生长分析

发布时间：2018-03-11 14:44

本文选题：热障涂层　切入点：高温氧化　出处：《湘潭大学》2017年硕士论文　论文类型：学位论文

【摘要】：热障涂层以其优异的隔热、耐磨和耐蚀性被广泛应用在航空涡轮发动机中,然而,热障涂层的几何形状、微观结构和服役环境都极其复杂,使得涂层在无法预知的情况下开裂,最终导致涂层剥落失效。在服役过程中,热生长氧化物(thermally grown oxide,TGO)在力、热、化学势多重因素作用下生长,极大地限制了TBCs在航空发动机上的安全应用。本文重点考虑了TGO在力化耦合作用下的生长,并借助有限元软件进行仿真模拟计算分析,主要研究内容和结果如下:第一,通过建立简单的高温氧化模型,研究氧化物厚度的演化规律,得到了TGO厚度与温度、氧分压、表面粗糙度等外部条件的解析表达式。进一步分析了温度、氧分压、表面粗糙度等外部环境条件对氧化层厚度的影响,结果表明:TGO氧化初期,生长速度很快,随着时间的增长,反应速度逐渐减小,最后趋于平稳;温度和表面粗糙度对氧化层厚度的影响较大,而氧分压对其影响较小;随着温度升高和表面粗糙度增加,氧化层的厚度越大并且氧化反应程度越高。第二,在小变形假设情况下,将总应变分为弹性应变和生长应变,通过生长应变建立TBCs高温氧化过程中浓度对力场的影响,建立TGO生长过程中的力场的本构关系;在化学势中加入平均应力,通过Fick定律建立力对化学场的影响,得到化学场的本构关系;在TBCs高温氧化过程中引入一个变量n来表示TGO的生长过程,当其取1表示TGO,取0表示粘结层,得到TGO的演化方程。结合力平衡方程、扩散反应方程、TGO演化方程以及本构方程建立TBCs高温氧化的力化耦合模型。第三,借助于COMSOL建立TGO生长的有限元模型,给定力场和化学场的边界条件及初始条件,将力化耦合理论的控制方程写成弱形式输入COMSOL,进而研究TGO生长和涂层内应力的耦合规律。结果表明:波峰处TGO氧化生长速率比波谷大,且TGO厚度随界面粗糙度的增加而增大;TBCs的界面粗糙度是影响涂层内应力分布的关键因素,随着粗糙度的增大,应力值在不断增加;涂层内的压应力对TGO生长有抑制作用,拉应力有促进作用。
[Abstract]:Thermal barrier coatings with excellent heat insulation, wear resistance and corrosion resistance has been widely used in aviation turbine engine, however, thermal barrier coating geometry, microstructure and service environment are extremely complex, which makes the coating cracking in the unpredictable situation, resulting in coating peeling failure. In the course of service, the thermally grown oxide (thermally grown oxide, TGO) in force, thermal, chemical potential growth under the effect of multiple factors, which greatly limits the security application of TBCs in aircraft engine. This paper focuses on the TGO under the coupling effect of growth in force, and simulation calculation and analysis of finite element software, the main research contents and results are as follows: 1. Through the establishment of high temperature oxidation model, the evolution of oxide thickness, the thickness of TGO and temperature, oxygen partial pressure, the analytical expression of surface roughness and other external conditions further. The analysis of the temperature, oxygen partial pressure, surface roughness and other external environmental conditions on the thickness of the oxide layer. The results showed that the oxidation of TGO at the early stage, growth is very fast, with the increase of time, the reaction rate decreases, finally tends to be stable; temperature and surface roughness of larger influence on the thickness of the oxide layers, and oxygen the pressure has little influence on it; with the increase of temperature and the surface roughness increases, the thickness of the oxide layer is larger and higher oxidation degree. In second, small deformation assumption, the total strain is divided into elastic strain and strain growth, establish the influence of the concentration of TBCs during high temperature oxidation of stress field by growing strain. The constitutive relation of the growth process established in TGO force field; with the average stress in the chemical potential, through the Fick law of influence on the chemical stress field, the constitutive relation of chemical field; the introduction of a high temperature in the process of oxygen in TBCs The variable n to represent the growth process of TGO, when the 1 TGO, 0 said adhesive layer, we obtain the evolution equation of TGO. Combined with the force balance equation, diffusion reaction equation, TGO evolution equation and constitutive equation of force coupling model of high-temperature oxidation of TBCs. Third, with the aid of the finite element in COMSOL building TGO the growth model of the given field and chemical field boundary conditions and initial conditions, the force control equations of the coupling theory in the weak form of input COMSOL, and TGO on the growth and coupling of the internal stress of coating. The results show that the peak of TGO oxidation growth rate than trough, and the thickness of the interfacial roughness of TGO the increase of TBCs; the interface roughness is a key factor affecting the distribution of the internal stress of coating, with the increase of roughness, the stress value increased; compressive stress within the coating could inhibit the growth of TGO, the tensile stress has a role in promoting.

【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG174.4

【参考文献】