真空热处理对APS-NiCoCrAlY+APS-YSZ热障涂层热循环寿命的影响

通过大气等离子喷涂在HA188合金基材上制备NiCoCrAlY+YSZ热障涂层,然后分别对试样在高真空和低真空中进行1080 ℃的热处理。通过在1100 ℃对热处理前后的热障涂层进行热循环考核,并在具备EDS的扫描电镜下分析了热循环前后的显微组织和成分。结果表明,真空热处理显著提高了APS-NiCoCrAlY+APS-YSZ热障涂层的热循环寿命,一方面是由于真空热处理后在APS-NiCoCrAlY/APS-YSZ界面上形成连续的TGO层受到了抑制,降低了由TGO产生的应力开裂,另一方面真空热处理后的涂层热循环时在APS-NiCoCrAlY的内部产生了更多的氧化物,在一定程度上降低了APS-NiCoCrAlY的热膨胀系数,减少了由APS-NiCoCrAlY/APS-YSZ热膨胀系数不匹配造成的应力开裂。并且低真空热处理的涂层内部失效裂纹没有像高真空热处理的涂层那样均匀连续扩展。     

热障涂层热疲劳寿命预测模型研究

目的 建立热障涂层寿命预测模型,并研究涂层寿命预测与各种应力应变信息的相关性。方法 首先利用带热障涂层圆管试验结果,将涂层界面简化为余弦曲线,建立了相应的二维轴对称有限元模型;然后根据热障涂层疲劳试验结果,结合线性疲劳累积理论和Manson–Coffin低周疲劳模型,建立了热障涂层的寿命预测模型,并将拟合问题转化为寻优问题,使用遗传算法确定寿命预测模型中的系数;最后基于热障涂层试验的微观照片确定出危险点位置,选取正向、剪切、等效和通过二向应力应变分析方法提取垂直于余弦曲面形貌的11种应力应变信息进行寿命预测,并分析了寿命预测的最大误差和平均误差,对分析的结果进行了验证。结果 采用等效应变范围进行涂层寿命预测的最大误差和平均误差最小,分别为50%和21%,涂层寿命与等效应力的相关性最大。采用等效应变进行寿命预测的结果与文献中的结果相比,最大误差降低了169.1%,整体的寿命预测值从±2倍分散带之内缩小到了±1.5倍分散带之内。采用等效应变范围进行不同工况下的涂层寿命预测,预测结果为130次循环,试验结果为160次循环,寿命预测的结果较好。结论 证明了所建立模型的正确性与准确性,为涂层寿命...     

EB-PVD工艺中粘结层厚度对热障涂层寿命的影响

采用电子束物理气相沉积技术在高温合金基体上制备不同粘结层厚度的YSZ热障涂层试样来分析粘结层厚度对热障涂层体系寿命的影响。对试样进行循环氧化试验以及热重分析来测试试样的热循环寿命和抗氧化性能。分别采用XRD、SEM和EDS对不同状态下的涂层进行相组成、微观形貌和成分组成分析。结果显示:热障涂层体系有明显的抗氧化作用,且抗氧化作用随着粘结层厚度的增加逐渐增强;粘结层的厚度对涂层体系的寿命影响显著,在特定的厚度范围内,涂层体系热循环寿命较长。综合各方面影响因素,得出本试验条件下粘结层厚度最优范围为50～70μm。     

热障涂层界面形貌尺寸与残余应力的关系

利用ANSYS有限元分析软件对热障涂层中的残余应力进行了模拟分析，得出了界面形貌尺寸与残余应力之间的关系。模拟结果表明，热障涂层中的残余应力是界面形貌尺寸的函数。这些结论为提高涂层界面结合强度的热障涂层界面造形提供了理论支持，也为热障涂层界面的优化提供了指导意见。     

热障涂层的三维界面形貌与热应力关系

使用等离子喷涂方法制备出双层热障涂层(粘结层为Ni-Cr-Al-Y,陶瓷层为ZrO2).使用ABAQUS有限元分析软件,采用间接耦合分析的方法,模拟计算了喷涂过程中陶瓷层/粘结层间三维结构椭圆界面的应力场分布,得出了粘结层表面三维椭球形貌单元位置和尺寸与热应力分布之间的关系.模拟结果表明,涂层制备后,椭球形貌单元位置和...     

界面粗糙度对双层热障涂层残余应力影响的数值模拟

运用ANSYS有限元分析软件模拟了双层热障涂层（ZrO2/NiCrAIY）在制备过程中的温度场，在此基础上，进行热-应力耦合计算分析试样的残余应力，重点计算了不同基体表面粗糙度条件下的残余应力分布。结果表明：试样的温度分布呈不均匀变化，与实际喷涂过程相近；双层热障涂层的最大残余应力集中在粗糙界面的凸起与凹坑部分；涂层内的等效残余应力随表面粗糙度的增大整体呈增大趋势，在Rα=30μm附近时，等效残余应力较小，同时压应力较小。     

粘结层表面处理对热障涂层残余应力及热冲击寿命的影响

采用真空电弧离子镀技术在二代单晶高温合金DD32表面制备NiCoCrAlYHf（HY5）金属粘结层,通过振动光饰、吹砂及振动光饰和吹砂3种不同的表面处理方法改变粘结层表面状态,利用电子束物理气相沉积（EB-PVD）技术制备氧化钇部分稳定氧化锆（7~8YSZ）陶瓷层。借助扫描电子显微镜（SEM）、电子探针（EPMA）、光激发荧光压电光谱（PLPS）等分析手段,研究1100 ℃热冲击过程中热障涂层界面结构、成分及残余应力的演变。结果表明:表面处理能够改善粘结层表面形貌,其对TGO层残余应力大小及热冲击寿命存在影响;未处理试样应力水平高于经过表面处理的热障涂层试样,并且随着热冲击次数的增加未处理试样残余应力涨幅更大;经过表面处理后试样热冲击寿命提高,其中经过振动光饰处理的试样提升最为显著;粘结层表面吹砂处理会造成砂粒进入粘结层表层某些部位,TGO层局部过度生长,造成应力集中,从而涂层寿命低于振动光饰处理试样。     

热障涂层界面形貌和尺寸对热应力的影响

为了研究航空发动机热障涂层的失效机制,以及涂层界面间的三维形貌对涂层热应力的影响,使用ABAQUS有限元分析软件,计算了陶瓷层/粘结层结合界面间6种三维凹坑和凸起形貌单元形状以及尺寸对界面主应力σyy分布的影响规律.结果表明,形貌单元对界面应力有明显的影响,凹坑形貌界面上应力为压应力,凸起应力为拉应力,在形貌最低和最高...     

耐久性柱状结构热障涂层设计

热障涂层（TBC）被广泛应用于热端金属部件表面,使其免受高温气体侵蚀,其微观组织结构及服役性能与制备工艺和服役状态密切相关并相互作用。本文从热生长氧化物（TGO）增厚、相变、烧结等方面讨论了各种应力诱因导致的TBC失效机理,综述了目前常用于陶瓷层柱状结构制备的方法及其在缓和TBC服役过程中应力的应用。由于TBC制备工艺及服役条件不尽相同,通过与标准TBC比较,评价了不同工艺下制备的TBC使用寿命,总结了柱状结构TBC的长寿命服役机理。本文综述了柱状热障涂层的应力源、微观结构、制备工艺和使用性能的相互作用关系,为高性能TBC设计提供了参考。     

表面处理对热障涂层寿命及失效机理的影响研究

采用真空电弧离子镀和电子束物理气相沉积技术在高温合金DZ125上沉积NiCrAlYSi金属粘结层和YSZ陶瓷面层。研究了抛光、振动光饰、砂纸打磨及吹砂四种不同的表面处理方法对金属粘结层表面微观结构和界面状态的影响。实验结果表明,四种表面处理方法都改善了金属粘结层表面结构,降低了表面粗糙度。进一步探讨了表面处理对涂层结合强度的作用,结果表明经过表面处理后的样品结合强度都得到了提高。并分析了不同表面处理方法对涂层寿命的影响,最终明确了热障涂层失效机理。     

混合氧化物对等离子喷涂热障涂层热循环寿命的影响

采用梯度热循环试验与理论模型相结合的方式研究了混合氧化物对热障涂层寿命的影响。喷涂态热障涂层系统由Inconel 738基体、冷喷涂沉积的NiCoCrAlTaY粘结层(BC)及大气等离子喷涂制备的ZrO2+Y2O3(8%)陶瓷层组成。在1 150℃空气气氛条件下,经过保温20h制备了含有混合氧化物的涂层。每个热循环包括70s的加热,50s的保温及120s的压缩空气冷却。陶瓷层表面最高温度为1 150℃,此时250μm厚的陶瓷层隔热150℃。结果表明:涂层中存在混合氧化物时,其寿命显著降低,且涂层寿命降低程度与混合氧化物和α-Al2O3生长诱发的YSZ应变量,以及混合氧化物的覆盖率有关。与α-Al2O3相比,较高生长速率的混合氧化物易诱发YSZ产生较高的应变,过早地诱发涂层未结合界面扩展、合并,进而导致涂层快速失效。     

Influence of Bondcoat Spray Process on Lifetime of Suspension Plasma-Sprayed Thermal Barrier Coatings

Development of thermal barrier coatings (TBCs) manufactured by suspension plasma spraying (SPS) is of high commercial interest as SPS has been shown capable of producing highly porous columnar microstructures similar to the conventionally used electron beam–physical vapor deposition. However, lifetime of SPS coatings needs to be improved further to be used in commercial applications. The bondcoat microstructure as well as topcoat–bondcoat interface topography affects the TBC lifetime significantly. The objective of this work was to investigate the influence of different bondcoat deposition processes for SPS topcoats. In this work, a NiCoCrAlY bondcoat deposited by high velocity air fuel (HVAF) was compared to commercial vacuum plasma-sprayed NiCoCrAlY and PtAl diffusion bondcoats. All bondcoat variations were prepared with and without grit blasting the bondcoat surface. SPS was used to deposit the topcoats on all samples using the same spray parameters. Lifetime of these samples was examined by thermal cyclic fatigue testing. Isothermal heat treatment was performed to study bondcoat oxidation over time. The effect of bondcoat deposition process and interface topography on lifetime in each case has been discussed. The results show that HVAF could be a suitable process for bondcoat deposition in SPS TBCs.     

Influence of Topcoat-Bondcoat Interface Roughness on Stresses and Lifetime in Thermal Barrier Coatings

Failure in Atmospheric Plasma-Sprayed (APS) thermal barrier coatings (TBCs) is associated with the thermo-mechanical stresses developing due to the thermally grown oxide (TGO) layer growth and thermal expansion mismatch during thermal cycling. The interface roughness has been shown to play a major role in the development of these induced stresses and lifetime of TBCs. Modeling has been shown as an effective tool to understand the effect of interface roughness on induced stresses. In the previous work done by our research group, it was observed that APS bondcoats performed better than the bondcoats sprayed with High Velocity Oxy-Fuel process which is contrary to the present literature data. The objective of this work was to understand this observed difference in lifetime with the help of finite element modeling by using real surface topographies. Different TGO layer thicknesses were evaluated. The modeling results were also compared with existing theories established on simplified sinusoidal profiles published in earlier works. It was shown that modeling can be used as an effective tool to understand the stress behavior in TBCs with different roughness profiles.     

Influence of TGO Composition on the Thermal Shock Lifetime of Thermal Barrier Coatings with Cold-sprayed MCrAlY Bond Coat

NiCoCrAlTaY bond coat was deposited by cold spraying to assemble thermal barrier coatings (TBCs). The microstructure of the cold-sprayed bond coat was examined using scanning electron microscopy. TBCs consisting of cold-sprayed bond coat and plasma-sprayed YSZ were pretreated at different conditions to form different thermally grown oxides (TGOs) before thermal cycling test. The influence of the TGO composition on the thermal cyclic lifetime was quantitatively examined through the measurement of the coverage ratio of the mixed oxides on the bond coat surface. The results showed that the bond coat exhibited a dense oxidation-free microstructure, and TGOs in different morphologies and constituents were present after thermal cyclic test. The formation of TGOs was significantly influenced by pretreatment conditions. Two kinds of TGO were detected on the surface of bond coat after the spallation of YSZ coatings. One is the α-Al₂O₃-based TGO and the other is the mixed oxide. It was found that the thermal cyclic lifetime is inversely proportional to the coverage ratio of the mixed oxides formed at the bond coat/YSZ interface. The high coverage ratio of the mixed oxide on the interface leads to the early spalling of YSZ coating.     

Bilayer Suspension Plasma-Sprayed Thermal Barrier Coatings with Enhanced Thermal Cyclic Lifetime: Experiments and Modeling

Suspension plasma spraying (SPS) has been shown as a promising process to produce porous columnar strain tolerant coatings for thermal barrier coatings (TBCs) in gas turbine engines. However, the highly porous structure is vulnerable to crack propagation, especially near the topcoat-bondcoat interface where high stresses are generated due to thermal cycling. A topcoat layer with high toughness near the topcoat-bondcoat interface could be beneficial to enhance thermal cyclic lifetime of SPS TBCs. In this work, a bilayer coating system consisting of first a dense layer near the topcoat-bondcoat interface followed by a porous columnar layer was fabricated by SPS using Yttria-stabilised zirconia suspension. The objective of this work was to investigate if the bilayer topcoat architecture could enhance the thermal cyclic lifetime of SPS TBCs through experiments and to understand the effect of the column gaps/vertical cracks and the dense layer on the generated stresses in the TBC during thermal cyclic loading through finite element modeling. The experimental results show that the bilayer TBC had significantly higher lifetime than the single-layer TBC. The modeling results show that the dense layer and vertical cracks are beneficial as they reduce the thermally induced stresses which thus increase the lifetime.     

基于临界失效能密度判据的热障涂层热震损伤行为研究

目的探索热障涂层系统(TBCs)在热震过程中的损伤行为。方法基于材料能量储存极限,推导了适用于平面复杂应力情形的温度相关性临界失效能密度判据,进而利用该临界失效能密度判据与ABAQUS有限元软件相结合,研究了热生长氧化层(TGO)凸起的热障涂层系统在冷却热震过程中的损伤行为。结果对于TGO层凸起的热障涂层系统,计算了冷却热震过程中陶瓷层(TC)和TGO层的失效能密度分布云图,并根据最大失效能分布情况分析了TBCs在热震过程中各层材料的可能破坏位置,所得结果与实验吻合较好。在对TBCs的冷却热震损伤行为模拟计算中发现,当TC层的强度比较低时,热震会使TC层上表面产生往内部扩展的垂直裂纹;当TC层强度达到某一定值时,首先发生热震破坏的位置由TC层上表面变成了TGO层与粘结层(BC)的界面处,即TBCs的各层破坏顺序发生了变化。结论使用临界失效能密度准则来判断热障涂层在冷却热震过程中的损伤行为,比单纯使用某一方向应力更为准确,并能准确判断损伤起始位置和演化情况,从而更全面地反映热障涂层在热震过程中的损伤破坏行为。     

Oxidation Resistance of Thermal Barrier Coatings Based on Hollow Alumina Particles

Thermal barrier coatings were synthesized in a single step process from a slurry containing Al microspheres onto different Ni-based superalloys. Upon growth of the coating a top coat of hollow alumina spheres linked to an aluminium diffused coating through an alumina TGO formed. The isothermal and cyclic oxidation tests at different temperatures (900 till 1100 °C) up to 1000 h or 1500 cycles revealed progressive growth of different thermal oxides depending on the substrate composition. Faster degradation of the coatings occurred in the titanium-rich substrates (e.g. IN-738LC and PWA1483) compared to the titanium-poor ones (CM-247LC and René N5). By comparing with conventional low activity aluminide coatings, it appeared that the incorporation of alloying elements (notably Ti and Ta) to the diffused layers upon the high activity slurry coating process is responsible for such fastest degradation.