【作者】 杨欢；

【导师】 花银群；

【作者基本信息】 江苏大学 ， 机械工程（专业学位）， 2022， 硕士

【摘要】 MCrAlY(M=Ni,Co,Ni+Co)型高温防护涂层因其具有优异的抗氧化和耐腐蚀性能,并且成分高度可控,既可单独用作高温防护涂层,又可作为热障涂层中陶瓷层与高温合金基体之间的过渡金属层。因此,该涂层被广泛应用于复杂高温工况下的航空发动机涡轮叶片和燃气轮机等热端部件。高温氧化期间,MCrAlY涂层表面会发生氧化反应生成一层热生长氧化物(Thermally-grown oxide,TGO)。一方面致密的TGO可以阻碍外部氧元素和内部金属元素(Ni、Co、Cr)的相互扩散和反应,提高涂层抗氧化性;另一方面,TGO非受控生长,会诱发有害应力,弱化涂层体系中界面的结合,导致涂层剥落。因此,调控TGO的生长演化过程,对提高MCrAlY高温防护涂层服役性能至关重要。本文通过激光冲击强化(Laser Shock Processing,LSP)表面改性技术对电弧离子镀(Arc Ion Plating,AIP)沉积的NiCoCrAlY涂层表面进行改性,对涂层表面微观形貌进行了有效的调控,实现了对TGO“遗传生长”和演化过程的干预及控制,在涂层内部引入大量位错、孪晶等缺陷,细化了涂层的晶粒,最终达到提高涂层抗高温氧化性能的目的。利用X射线衍射仪、三维激光扫描显微镜、残余应力测试仪、扫描电子显微镜、透射电子显微镜等表征手段,详细表征了激光冲击前后涂层的微观形貌,残余应力,高温氧化过程中TGO的演化。研究了激光冲击强化作用下,涂层表面微观组织、TGO生长和高温服役性能三者之间的关系,为提高MCrAlY型涂层及热障涂层服役寿命提供了重要参考。本文主要的研究内容和结论如下:(1)数值研究激光冲击NiCoCrAlY涂层动态过程,优化激光冲击工艺参数。基于ABAQUS有限元平台建立了激光冲击处理AIP-NiCoCrAlY涂层的三维模型,计算激光能量、冲击次数、搭接率等关键参数对涂层内部、涂层-基体界面应力状态的影响规律,结果发现针对涂层类的双层结构,为确保对涂层有改性效果,同时防止界面损伤,需要采用小能量多次冲击的工艺方案。(2)实验研究激光冲击对NiCoCrAlY涂层表面形貌、组织应力等影响规律。基于数值研究结果,优选激光工艺参数对AIP制备的NiCoCrAlY涂层进行激光冲击实验。结果表明:NiCoCrAlY涂层经过激光冲击处理后,降低了涂层表面粗糙度,有效改善了涂层表面大颗粒的问题;引入了高密度位错、层错、针状孪晶等晶格缺陷;γ/γ′相的衍射峰向高角度偏移,衍射峰发生明显宽化,有明显的晶粒细化效果。涂层内缺陷增多以及晶粒细化可为元素扩散提供了更多通道。涂层内引入了300～600MPa的残余压应力。(3)激光冲击改性NiCoCrAlY涂层的等温氧化性能研究。对不同激光冲击参数制备的涂层进行1100℃恒温氧化行为分析。研究结果表明:Non-LSP样品氧化后表现出三个阶段的生长行为:(I)初始快速生长阶段、(II)稳定生长阶段和(III)加速生长阶段;相比之下,LSP处理的样品在整个氧化过程中表现出非常低的氧化率,只有两个阶段:(I)初始快速生长阶段和(II)扩展稳定生长阶段。氧化150h后,Non-LSP样品出现氧化膜损伤和大面积内氧化。LSP改性后的样品表现良好,形成了一层保护性连续的氧化铝膜,因此保持了更长的稳定氧化阶段。多次激光冲击可能会在涂层中引入微裂纹等缺陷,这对后期的高温氧化行为极为不利。因此,在利用激光冲击进行表面改性的过程中,还应注意激光冲击参数的优化。更多还原

【Abstract】 MCrAlY(M=Ni,Co,Ni+Co)type high temperature protective coating has excellent oxidation resistance and corrosion resistance,and its composition is highly controllable.It can be used as a high temperature protective coating alone or as a thermal barrier coating.The transition metal layer between the medium ceramic layer and the superalloy substrate.Therefore,the coating is widely used in hot end components such as aero-engine turbine blades and gas turbines under complex high temperature conditions.During high temperature oxidation,an oxidation reaction occurs on the surface of the MCrAlY coating to form a thermally-grown oxide(TGO).On the one hand,dense TGO can prevent the mutual diffusion and reaction of external oxygen elements and internal metal elements(Ni,Co,Cr),and improve the oxidation resistance of the coating;on the other hand,the uncontrolled growth of TGO will induce harmful stress and weaken the Interfacial bonding in the coating system,resulting in coating peeling.Therefore,regulating the growth and evolution of TGO is crucial to improve the service performance of MCrAlY high temperature protective coatings.In this paper,the surface of NiCoCrAlY coating deposited by Arc Ion Plating(AIP)was modified by Laser Shock Processing(LSP)surface modification technology,and the surface morphology of the coating was effectively controlled.The intervention and control of the "genetic growth" and evolution process of TGO are realized,a large number of defects such as dislocations and twins are introduced into the coating,the grains of the coating are refined,and the purpose of improving the high temperature oxidation resistance of the coating is finally achieved.Using Xray diffractometer,scanning electron microscope,transmission electron microscope,threedimensional laser scanning microscope,residual stress tester and other characterization methods,the microscopic morphology of the coating before and after laser shock,the residual stress,and the evolution of TGO during high temperature oxidation were characterized in detail.process.The relationship between the surface microstructure,TGO growth and high temperature service performance of the coating under the action of laser shock strengthening was studied,which provided an important reference for improving the service life of MCrAlY type coatings and thermal barrier coatings.The main research contents and conclusions of this paper are as follows:(1)Numerically study the dynamic process of laser shock NiCoCrAlY coating and optimize the laser shock process parameters.Based on the ABAQUS finite element platform,a threedimensional model of the laser shock treatment AIP-NiCoCrAlY coating was established,and the influence of key parameters such as laser energy,impact times,and overlap ratio on the stress state inside the coating and the coating-substrate interface was calculated.The results found that for the double-layer structure of the coating type,in order to ensure the modification effect of the coating and prevent the interface damage at the same time,it is necessary to adopt a process scheme of small energy and multiple impact.(2)The effects of laser shock on the surface morphology and microstructure stress of NiCoCrAlY coatings were experimentally studied.Based on the numerical research results,laser shock experiments were performed on NiCoCrAlY coatings prepared by AIP with optimized laser process parameters.The results show that: after laser shock treatment of NiCoCrAlY coating,the surface roughness of the coating is reduced,and the problem of large particles on the surface of the coating is effectively improved;lattice defects such as high-density dislocations,stacking faults,and needle twins are introduced;The diffraction peaks of the γ/γ’ phase shift to high angles,and the diffraction peaks are obviously broadened,and the grain refinement effect is obvious.Increased defects within the coating and grain refinement provide more channels for element diffusion.The residual compressive stress of 300～600MPa is introduced into the coating.(3)Isothermal oxidation properties of laser shock modified NiCoCrAlY coatings.The oxidation behavior of coatings prepared with different laser shock parameters was analyzed at1100 ℃ constant temperature.The results showed that the Non-LSP samples exhibited three stages of growth behavior after oxidation:(I)initial rapid growth stage,(II)stable growth stage and(III)accelerated growth stage;in contrast,LSP-treated samples Exhibiting a very low oxidation rate throughout the oxidation process,there are only two stages:(I)an initial rapid growth stage and(II)an extended stable growth stage.After 150 h of oxidation,the Non-LSP samples showed oxide film damage and large-area internal oxidation.The LSP-modified samples performed well,forming a protective continuous alumina film,thus maintaining a longer stable oxidation stage.Multiple laser shocks may introduce defects such as microcracks in the coating,which are extremely detrimental to the later high-temperature oxidation behavior.Therefore,in the process of surface modification by laser shock,attention should also be paid to the optimization of laser shock parameters.更多还原