【作者】 高雪松；

【导师】 黄因慧；

【作者基本信息】 南京航空航天大学 ， 机械制造及其自动化， 2011， 博士

【摘要】 陶瓷材料由于具有优异的耐磨、耐蚀、耐热和抗高温氧化性能，而使其成为金属防护涂层的首选。但由于陶瓷涂层材料与金属基体材料在物理性能方面存在较大差异，使得现有表面技术在基体表面制备的陶瓷涂层，其结合力低，在高温环境中使用，涂层在温度变化中会产生较大内应力，容易涂层剥落。本文以高结合强度(超过传统的等离子喷涂及激光熔覆等离子喷涂制备的涂层结合强度，同时，在高温的使用过程中，结合强度的提高能够改善涂层的使用寿命)为目标，基于激光熔覆技术，利用高频感应辅助的方法，对陶瓷涂层的制备进行了基础研究。在镍基高温合金表面成功制备了MCrAlY/Al2O3-13％TiO2陶瓷涂层以及具有微孔结构黏结层的Al2O3-13％TiO2陶瓷涂层。对上述两种涂层进行对比研究。针对于所制备的陶瓷涂层，本文首先从激光与陶瓷材料相互作用的机理着手，对激光的作用模型进行分析。通过实验与理论相结合的方式对激光与陶瓷的相互作用模型进行探讨研究。在激光的作用下，陶瓷材料的烧结主要分为吸收、烧结、凝固三个步骤进行。根据烧结过程的机理，选用Al2O3-13％TiO2陶瓷材料进行实验分析。从中得出，陶瓷材料的颗粒形状、尺寸及密度对陶瓷材料的烧结性能影响较大。当陶瓷材料尺寸达到纳米量级，呈球型时其烧结性能最优越，陶瓷材料的烧结性能随着坯体的致密度的增加而增加。而激光温度场对陶瓷材料的烧结性能影响较大，温度更加均匀的温度场将会减小陶瓷材料形成裂纹的热应力，晶粒之间析出明显，但尺寸有所增加。根据现有高温陶瓷涂层的失效机理进行分析判断，提出了高结合强度陶瓷涂层整体设计方案。基于激光熔覆技术，设计了MCrAlY/Al2O3-13％TiO2陶瓷涂层以及具有微孔结构黏结层的Al2O3-13％TiO2陶瓷涂层。MCrAlY/Al2O3-13％TiO2陶瓷涂层采用传统的涂层设计理念，利用MCrAlY黏结层缓解陶瓷层与基体金属之间的物理性能差异，同时对设计涂层进行可行性验证。结果表明，在预置高致密度陶瓷粉体后，通过高频感应辅助激光熔覆技术可以成功制备上述设计涂层。基于高温工作原理的需求，本文设计了一种具有微孔结构黏结层的Al2O3-13％TiO2陶瓷涂层，将黏结层设计成为微孔结构，利用微孔结构的高抗热震性、低热膨胀系数的特点减少黏结层与陶瓷层之间的热应力，使得涂层具有更加优异的高温性能。同样，对激光烧结微孔金属进行了可行性验证，以使得涂层的设计更加具有科学性。利用SEM、XRD等分析手段对MCrAlY/Al2O3-13％TiO2陶瓷涂层和具有微孔结构黏结层的Al2O3-13％TiO2陶瓷涂层的组织结构、成分进行了详细分析。MCrAlY/Al2O3-13％TiO2陶瓷涂层界面元素明显扩散，呈现良好的化学结合特性，体现了涂层的高结合强度；而具有微孔结构黏结层的Al2O3-13％TiO2陶瓷涂层则由于黏结层材料成分改变及多孔特性的原因，使得涂层界面之间没有明显的扩散现象。但由于微孔的铆接作用，陶瓷层与黏结层依旧结合紧密。对上述制备试样进行了结合强度、高温氧化实验、热震实验综合实验，以判断涂层的高温结合性能及失效形式。结果表明，MCrAlY/Al2O3-13％TiO2陶瓷涂层具有很高的结合强度及抗高温氧化性能，但随着热震次数的增加其结合强度大幅度下降。结合残余应力测试综合分析，该系列涂层产生的热应力较大，容易产生微裂纹，适合在低温条件下使用。具有微孔结构黏结层的Al2O3-13％TiO2陶瓷涂层结合强度略低，但体现了良好的高温抗氧化性能及高温抗热震性能。其最终为热疲劳失效。综合上述研究结果，本文对激光原位自生陶瓷涂层进行了研究。采用MCrAlY/Al系反应材料，基于激光熔覆技术，利用Al元素原位氧化形成Al2O3原理，原位生成厚度原位40m的陶瓷层。涂层的微观结构表明，陶瓷层与反应层之间结合相当紧密，且在界面处生成大量晶须，这将大大增加涂层之间的结合力，说明该方法是一种非常有应用前景的陶瓷涂层制备工艺。更多还原

【Abstract】 Ceramics are priority applied for protective coating because of their excellent wear and corrosionresistance, heat resistance and high temperature oxidation resistance. However, ceramic coating showlow adhesion prepared by surface coating technique due to huge difference of Ceramic coatingmaterial and metal matrix material in physical performance. Ceramic coatings are easy to failure as aresult of huge thermal stress in the high temperature environment. In the paper, a fundamentalresearch on the high bonding strength ceramic coating prepared by laser cladding. A series of researchon the samples of MCrAlY/Al2O3-13％TiO2ceramic coating and microporous structure adhesivelayer/Al2O3-13％TiO2ceramic coating, which prepared by high frequency assisted laser cladding.Prepared for the ceramic coating, firstly, the sintering mechanism of the mechanism of ceramicmaterials under the action of laser was researched. Meanwhile, the model of laser was analyzed. Aresearch on the mechanism was carried out according to combination of experimental and theoreticalmethods. It can be divided into absorption, sintering, solidification three stages during ceramicmaterials sintering. According to the mechanism of sintering process, Al2O3-13％TiO2ceramic wereuse to experimental analysis. The result showed that, ceramic particle, shape, size and density have asuperior influence on the sintering properties of ceramic materials. Ceramic sintering was the mostsuperior performance when the size reaches the nanometer ceramic and spherical shape. Meanwhile,sintering properties of ceramic were increased significantly with the density of green body increases.While the temperature field of laser has a superior influence on sintering properties of ceramicmaterials. The thermal stress which induced microcrack will be reduced when the uniformtemperature field, and the separation was precipitated between the grains, but the size increased.A whole design scheme of high bonding strength was proposed according to the existingmechanism of high temperature ceramic coating failure analysis. It is designed MCrAlY/Al2O3-13％TiO2ceramic coating and microporous structure adhesive layer/Al2O3-13％TiO2ceramic coatingprepared based on idea of laser cladding. MCrAlY/Al2O3-13％TiO2ceramic coatings useconventional coating design. It is used MCrAlY bond layers reduce the differences of physicalproperties between the ceramic layer and matrix metal. Meanwhile, the feasibility verifying tests arecarried under different cladding conditions. The results showed that, ceramic coating can be preparedby high frequency assisted laser cladding pre-high density ceramic powder. A creative design whichproposed based on the needs of high-temperature work, it is microporous structure adhesive layer/Al2O3-13％TiO2ceramic coating. In the design, the adhesive layer is designed to be porousstructure, ceramic coating will has excellent high temperature properties result of microporousstructure has a high thermal shock resistance, low thermal expansion coefficient, can be used toreduce thermal stress of ceramic layer and matrix metal. Similarly, the feasibility verifying tests ofmicroporous structure sintering by laser are carried in order to prove scientific of the coating design.Scanning electron microscopy (SEM) and X-ray diffraction (XRD) was applied to analyze thecomposition and microstructure of the MCrAlY/Al2O3-13％TiO2ceramic coating and microporousstructure adhesive layer/Al2O3-13％TiO2ceramic coating. The result showed that, MCrAlY/Al2O3-13％TiO2ceramic coating has a excellent chemical combination due to elements obviouslydiffused in the interface, will increase bonding strength of coating. In comparison with MCrAlY/Al2O3-13％TiO2ceramic coating, There is no obvious elements diffused in the interface ofmicroporous structure adhesive layer/Al2O3-13％TiO2ceramic coating result of the existence of alarge number of holes and changes in composition of adhesive layer. However, the interface is stilltightly under the action of microporous riveting.In order to estimate high temperature properties and failure mode of coating, bonding strength,high temperature oxidation and thermal shock of coating samples were tested respectively. The resultsshowed that MCrAlY/Al2O3-13％TiO2ceramic coating has good bonding strength and excellenthigh-temperature oxidation resistance, however，bonding strength of coating dramatically decreasedwith increasing thermal shock times. The microcracks are easily formed in the high temperature resultof huge thermal stress by residual stress test, add to use at low temperatures. Comparatively,microporous structure adhesive layer/Al2O3-13％TiO2ceramic coating had a slightly lower bondingstrength and excellent high-temperature oxidation resistance, but displayed a good thermal shockresistance. Final failure mode is thermal fatigue failure.Comprehensive result of work, a research on in-situ ceramic coating prepared by laser claddingwas carried out. MCrAlY/Al were used to in-situ about40mceramic coating prepared by lasercladding according to principle of Al in-situ oxidation. The result of study on microstructure showedthat in-situ ceramic coating and reaction layer combined closely to each other, meanwhile, there are alot of whiskers formed in the interface of the coating, the bonding strength will greatly increase，shows that the method is a very promising preparation of ceramic coatings.更多还原