Ba(Mg1/3Ta2/3)O3热障涂层的制备及抗热震性能研究

本文以BaCO₃、MgO、Ta₂O₅为原料,采用固相反应法合成了Ba(Mg_1/3Ta_2/3)O₃(简称BMT)陶瓷粉末,利用大气等离子喷涂技术制备了BMT/YSZ双层陶瓷涂层。利用XRD、SEM和金相显微镜检测了BMT粉体及涂层的物相组成和显微结构。采用水淬法考核了涂层的抗热震性能。结果表明：1450℃下煅烧4h可合成出具有复合钙钛矿结构的BMT粉末,粉末具有良好的高温相结构稳定性。等离子喷涂制备的BMT/YSZ涂层组织致密,涂层系统中各界面结合紧密。涂层在室温至1150℃间热震9次后发生片状剥落,剥落位置位于BMT层间,BMT材料低的断裂韧性和第二相Ba₃Ta₅O₁₅的存在是导致涂层失效的主要原因。     

高韧性过渡层对大气等离子喷涂热障涂层性能的影响EI北大核心CSCD

高温服役环境下,大气等离子喷涂(APS)制备的纳米结构热障涂层受热应力作用,黏结层/陶瓷层界面附近的陶瓷层内部易形成横向裂纹而导致热障涂层失效。利用常规大气等离子喷涂和超音速等离子喷涂(SAPS)制备8YSZ高韧性过渡层。结果表明,采用APS和SAPS制备的高韧性过渡层提高了扁平化粒子间结合状态和涂层致密度,相比常规结构8YSZ涂层的断裂韧性分别提高约46%和84%,高韧性过渡层均提高了复合结构热障涂层结合强度、抗热震性能和燃气热冲击寿命,SAPS制备的高韧性过渡层厚度为30~50μm时复合结构热障涂层抗热震性能最优,当高韧性过渡层厚度为10~30μm时,相比常规结构热障涂层燃气热冲击寿命提高120%。在温度梯度作用下,热障涂层最终失效由陶瓷层逐层剥落转变为靠近陶瓷层/黏结层界面处剥落。通过高韧性过渡层设计,兼顾热障涂层的隔热性能的同时,提高了热障涂层的结合强度和寿命。     

热喷涂可磨耗涂层的三维显微结构

采用超音速火焰喷涂和大气等离子喷涂在高温合金表面制备由金属粘结层NiCoCrAlYTa和陶瓷面层Dy₂O₃稳定的ZrO₂组成的可磨耗涂层,利用X射线显微镜（XRM）对涂层三维微观结构进行表征,结合扫描电子显微镜对经高温后的涂层孔隙、界面及裂纹演变进行研究。结果表明：在1100 ℃高温氧化条件下,随着氧化时间增加,粘结层中的富Ta相逐渐溶解并向晶界扩散,60 h后Ta元素完全固溶;粘结层/面层界面处形成双氧化层,由较致密均匀的氧化铝内层和混合氧化物外层构成;涂层的剥落失效主要由涂层中的裂纹缺陷导致,其在高温下优先沿界面、贯穿孔隙扩展。     

Al_2O_3/MoS_2复合涂层的制备及摩擦磨损性能

以大气等离子喷涂工艺制备的Al_2O_3陶瓷涂层为模板,利用陶瓷涂层中存在的孔隙和微裂纹,采用水热反应在其内部原位合成具有润滑特性的MoS_2,制备出Al_2O_3/MoS_2的复合涂层。结果表明,通过水热反应在陶瓷涂层原有的微观缺陷中成功合成了MoS_2,合成的MoS_2固体粉末呈类球形状,并且这球状的粉末是由纳米片层状的MoS_2搭建组成的。摩擦试验结果表明,与纯Al_2O_3涂层相比,复合涂层中由于MoS_2润滑膜的形成,其摩擦因数和磨损率都显著降低,且载荷越大,复合涂层的摩擦性能越好。     

铁基表面碳化钛致密陶瓷层的组织性能与增韧机制

利用铸渗复合-热处理工艺在铁基体表面原位制备了致密碳化钛陶瓷增强复合材料,分别研究了复合材料的物相组成、微观组织及细观组织、显微硬度、断裂韧性. 结果表明,钛板中的钛原子和石墨片中溶解析出的碳原子扩散到冶金结合面原位生成了碳化钛致密陶瓷层,且致密陶瓷层与钛板、致密陶瓷层与基体之间结合良好,界面干净. 致密陶瓷层显微硬度平均值为3 027.08 HV0.1,远远大于基体硬度和残余钛板硬度,试样纵截面致密陶瓷层在20 N载荷下在压痕顶端萌生,扩展了裂纹,其断裂韧性为4.5～14.2 MPa·m1/2,远高于一般的陶瓷材料.     

PS-PVD制备粘结层及其对热障涂层性能的影响

目的探究真空热处理对PS-PVD制备的粘结层的影响,并研究PS-PVD制备粘结层对热障涂层性能的影响。方法采用PS-PVD技术在高温合金基体上制备不同材料体系的粘结层和陶瓷层,采用真空热处理和高温氧化试验,对粘结层与基体界面间的元素扩散过程以及不同材料粘结层对热障涂层抗氧化性能的影响进行研究,并通过X射线衍射和EDS能谱对涂层的物相及元素分布进行分析。结果通过PS-PVD制备的不同粘结层体系的热障涂层试样,在近粘结层处的陶瓷层物相组成并无明显区别。粘结层与基体的元素扩散情况受真空热处理时间和温度的影响,随着真空热处理时间的延长,基体一侧的富铝相逐渐增多。当热处理8 h后,形成的扩散区的宽度已超过20μm;随着热处理温度的提高,同样也形成了更宽的扩散区。NiCoCrAlYTa/7YSZ热障涂层氧化100h后,TGO层的厚度达到4.0μm,氧化150h时,涂层发生脱离。NiCrAlY/7YSZ热障涂层氧化150 h后,TGO层的厚度达到4.4μm,但未出现脱离现象。结论热处理的时间越长,温度越高,粘结层与基体的元素扩散行为越剧烈。不同的粘结层材料会影响热障涂层的氧化动力学过程。     

铌表面MoSi2高温涂层的形貌和结构研究

用料浆熔烧法在铌基体表面制备了。MoSi2高温抗氧化涂层。利用SEM，EDS，XRD等仪器分析研究了涂层的结构、元素分布、相分布与抗氧化性能的关系。结果表明：涂层与基体之间达到了冶金结合，通过扩散形成了过渡层，涂层的复合结构有利于提高抗氧化性能，用料浆熔烧法在铌基体表面制备MoSi2涂层是可行的。在氧化环境下，MoSi2涂层能在表面自生成一层SiO2玻璃层，阻止氧的进一步扩散。经2h以上高温氧化后，Si的扩散使涂层主体中形成多孔疏松组织。涂层元素与基体发生互扩散，在界面处形成大量集中孔洞并横向贯穿，使涂层从其主体与过渡层接触的界面处发生横向内部断裂，导致涂层失效。     

等离子喷涂ZrO2-NiCoCrAlY梯度热障涂层的抗热震性及失效机理

研究了ZrO2-NiCoCrAlY热障涂层的抗热震性和热震失效机理.实验结果表明,梯度热障涂层能明显延缓热震裂纹的形成和扩展,具有较高的抗热震性.热震裂纹形成与扩展主要在粘结层与基体的界面处.随热循环次数的增加,热震裂纹可在表面陶瓷层内和陶瓷层与过渡层的界面处形成.实验表明热障涂层热震失效的过程主要是裂纹形成、扩展及涂层剥落,粘结层的氧化是导致涂层剥落失效的重要原因.     

钼合金MoSi2涂层高温热震行为与裂纹扩展

采用料浆烧结法在钼合金表面制备了MoSi₂涂层,利用内热法测试了涂层室温～1600℃抗热震性能,通过扫描电镜(SEM)、电子探针(EPMA)、波谱分析(WDS)和X射线衍射(XRD)等测试手段分析了不同热震次数的涂层微观形貌、组织结构以及裂纹萌生扩展。结果表明：涂层可承受室温～1600℃热震400次,热震过程中涂层由原始的MoSi₂-Mo₅Si₃双层结构演变为SiO₂-MoSi₂-Mo₅Si₃多层结构,涂层热震初期形成纵向裂纹并不断向基体扩展,热震后期裂纹贯穿涂层到达基体,MoO₃挥发使涂层/基体界面应力增大产生横向裂纹,导致涂层剥落失效。     

采用辅助脉冲电流液相扩散连接Ti(C,N)-Al_2O_3的接头形成行为及强度

采用辅助脉冲电流液相扩散连接方法,对Ti(C,N)-Al2O3陶瓷基复合材料与40Cr钢进行了焊接试验,重点研究了在辅助脉冲电流作用下,界面及焊缝组织演变、基体材料溶解等界面行为,探讨了工艺参数对接头强度及断口形态影响规律.结果表明,通过采用辅助脉冲电流液相扩散连接Ti(C,N)-Al2O3与40Cr钢,可以在较短的焊接时间条件下获得较为稳定的接头强度,四点弯曲平均强度位于231~272 MPa之间;降低焊接件整体加热温度以缓解接头残余应力,控制界面和焊缝化学冶金反应进程以较少金属间化合物数量、提高固溶体含量,抑制活性元素Zr向陶瓷基复合材料中的扩散进程以减少陶瓷颗粒向焊缝中的溶解量,是提升焊接接头强度的关键因素.     

等离子喷涂ZrO2—NiCoCrAlY梯度热障涂层的抗热震性及失效机理

研究了ZrO2-NiCoCrAlY热障涂层的抗热震性和热震失效机理。实验结果表明,梯度热隙涂层能明显延缓热震裂纹的形成和扩展,具有较高的抗热震性。热震裂纹形成与扩展主要在粘结层与基体的界面处。随热循环次数的增加,热震裂纹可在表面陶瓷层内和陶瓷层与过渡层的界面处形成。实验表明热障涂层热震失效的过程主要是裂纹形成、扩展及涂层剥落,粘结层的氧化是导致涂层剥落失效的重要原因。     

热浸铝钢等离子体电解氧化陶瓷层的微观力学特性

采用纳米压入方法表征了热浸镀铝钢表面由Al2O3层、Al层和FeAl层组成的复合涂层的纳米硬度、弹性模量及断裂韧性等微观力学性能,采用扫描电镜(SEM)观察了纳米压痕形貌,并分析了孔洞对陶瓷层的纳米压入行为和压痕裂纹扩展的影响.结果表明:等离子体电解氧化(PEO)陶瓷层中包含许多微米和亚微米尺度的细小孔洞,陶瓷层弹性模量约为226.4 Gpa,纳米硬度约为19.6 Gpa.当纳米压入深度为250 nm时,所测得陶瓷层的力学参数分散性较大.与FeAl层比较,PEO陶瓷层具有较高的裂纹扩展阻力. FeAl层纳米压痕顶端产生了沿直线扩展的径向裂纹;而陶瓷层纳米压痕中除径向裂纹外出现了侧边裂纹.     

Study of fracture behaviour of bond coats on nickel superalloy by three-point bending of microbeams

A microbeam testing geometry is designed to study the variation in fracture toughness across a compositionally graded NiAl coating on a superalloy substrate. A bi-material analytical model of fracture is used to evaluate toughness by deconvoluting load–displacement data generated in a three-point bending test. It is shown that the surface layers of a diffusion bond coat can be much more brittle than the interior despite the fact that elastic modulus and hardness do not display significant variations. Such a gradient in toughness allows stable crack propagation in a test that would normally lead to unstable fracture in a homogeneous, brittle material. As the crack approaches the interface, plasticity due to the presence of Ni₃Al leads to gross bending and crack bifurcation.     

硬质陶瓷涂层增韧及其评估研究进展

硬质陶瓷涂层一般硬度高,但韧性差,在受到较大外加冲击荷载作用时容易产生裂纹并引发失效,从而限制了硬质涂层在工程领域的应用。硬质涂层的增韧研究是当前硬质涂层研究的热点之一。常见硬质涂层增韧方法中,有些是以降低硬度为代价来提高涂层韧性,比如第二相增韧;有些是通过优化涂层结构设计,减小缺陷尺寸,在不损失涂层高硬度的前提下,提高韧性,获得兼具高硬度和高韧性的涂层;有些是通过相变(晶体结构转变)提高涂层的韧性。通过优化涂层结构设计,改变涂层晶粒尺寸、晶界尺寸与复杂程度等,使涂层致密化,从而提高涂层硬度与韧性,从而获得增韧效果,成为研究者越来越关注的焦点。单一增韧方法的局限性,可以通过多种增韧方法协同作用获得突破,协同增韧已成为硬质涂层增韧发展的趋势。目前硬质涂层的韧性评估还没有一个公认的方法,从简单实用出发,常用的有微悬臂梁弯曲法、划痕法和压痕法。     

粘结层预处理对PS-PVD沉积7YSZ热障涂层氧化行为的影响

目的提高PS-PVD沉积7YSZ热障涂层的抗高温氧化性能。方法采用等离子喷涂-物理气相沉积(PS-PVD)分别在未预处理和预处理(抛光+预氧化)的粘结层表面制备了柱状结构7YSZ热障涂层,并在大气环境下测试了柱状结构7YSZ热障涂层的950℃静态高温氧化性能。利用扫描电子显微镜、X射线衍射仪、能谱仪对高温氧化过程中的陶瓷层/粘结层界面形貌、TGO层结构演变进行表征。结果粘结层的抛光处理能够降低表面几何受力不均匀部位,抑制陶瓷层/TGO/粘结层界面处微裂纹的产生,同时粘结层的预氧化处理形成的薄而连续的TGO层能有效降低TGO的生长速度,抑制陶瓷层-粘结层之间的元素互扩散。柱状结构7YSZ涂层的高温氧化动力学曲线符合Wagner抛物线规律,粘结层未预处理和预处理的7YSZ热障涂层的氧化速率常数分别为0.101×10~(-12) cm~2/s和0.115×10~(-13) cm~2/s。结论粘结层预处理能有效改善等离子物理气相沉积7YSZ热障涂层的抗氧化性能。     

Fracture mechanics analysis of microcracks in thermally cycled thermal barrier coatings

The effects from thermal shock loading on pre-existing microcracks within thermal barrier coatings (TBCs) have been investigated through a finite element based fracture mechanical analysis. The TBC system consists of a metallic bond coat and a ceramic top coat. The rough interface between the top and bond coats holds an alumina oxide layer. Stress concentrations at the interface due to the interface roughness, as well as the effect of residual stresses, were accounted for. At the eventual closure between the crack surfaces, Coulomb friction was assumed. To judge the risk of fracture from edge cracks and centrally placed cracks, the stress intensity factors were continuously monitored during the simulation of thermal shock loading of the TBC. It was found that fracture from edge cracks is more likely than from centrally placed cracks. It was also concluded that the propagation of an edge crack is already initiated during the first load cycle, whereas the crack tip position of a central crack determines whether propagation will occur.     

Microstructure and Wear Resistance Evolution of HVOFSprayed WC-（W,Cr）2C-Ni Coating with Post Heat Treatment In Air Atmosphere

WC-(W,Cr)2C-Ni coating was prepared on 1Cr18Ni9Ti stainless steel and C-276 Ni-base Hastelloy by high velocity oxy-fuel(HVOF)spraying.The effect of post heat treatment in air atmosphere on the microstructure,phase composition,microhardness,fracture toughness,and wear resistance of HVOF-sprayed WC-(W,Cr)2C-Ni coating was investigated.The microstructure and phase composition of the coatings were analyzed by means of field emission scanning electron microscopy(FESEM)and X-ray diffraction(XRD).The microhardness and fracture toughness of the coatings were measured using a microhardness tester and a Vickers hardness tester.Moreover,dry friction and wear behavior of the coatings sliding against Si3N4 ball was investigated using an oscillating friction and wear tester;and the worn surfaces of the coatings were analyzed by means of scanning electron microscopy(SEM).It was found that heat treatment within 500-800°C resulted in crystallization of amorphous phase in as-sprayed coating,generating nanoscale new phases such as NiWO4,CrWO4 and Cr2WO6.Besides,heat treatment led to increase of the microhardness of as-sprayed coating,and the highest microhardness was obtained after heat treatment at 800°C.The fracture toughness and wear resistance of the as-sprayed coating increased with increasing heat treatment temperature up to 700°C but tended to decrease with further elevating temperature.In other words,the mechanical properties and wear resistance of the as-sprayed coatings were worsened owing to excessive growth of oxidation grains and depletion of ductile Ni binder after heat treatment above 700°C.Thus it was suggested that as-sprayed ceramic composite coating should be post heat treated in air at a moderate temperature of 700°C so as to achieve the optimized mechanical properties and wear resistance.     

TGO Growth and Crack Propagation in a Thermal Barrier Coating

In thermal barrier coating (TBC) systems, a continuous alumina layer developed at the ceramic topcoat/bond coat interface helps to protect the metallic bond coat from further oxidation and improve the durability of the TBC system under service conditions. However, other oxides such as spinel and nickel oxide, formed in the oxidizing environment, are believed to be detrimental to TBC durability during service at high temperatures. It was shown that in an air-plasma-sprayed (APS) TBC system, postspraying heat treatments in low-pressure oxygen environments could suppress the formation of the detrimental oxides by promoting the formation of an alumina layer at the ceramic topcoat/bond coat interface, leading to an improved TBC durability. This work presents the influence of postspraying heat treatments in low-pressure oxygen environments on the oxidation behavior and durability of a thermally sprayed TBC system with high-velocity oxy-fuel (HVOF)-produced Co-32Ni-21Cr-8Al-0.5Y (wt.%) bond coat. Oxidation behavior of the TBCs is evaluated by examining their microstructural evolution, growth kinetics of the thermally grown oxide (TGO) layers, and crack propagation during low-frequency thermal cycling at 1050 °C. The relationship between the TGO growth and crack propagation will also be discussed.     

Dependency of fracture toughness of plasma sprayed Al<Subscript>2</Subscript>O<Subscript>3</Subscript> coatings on lamellar structure

The fracture toughness of plasma-sprayed Al₂O₃ coatings in terms of critical strain energy release rate G _Ic was investigated using a tapered double cantilever beam (TDCB) approach. This approach makes the fracture toughness be measured only using the critical fracture load disregarding crack length during test. The Al₂O₃ coatings were deposited under different spray distances and plasma powers to clarify the effect of spray parameters on the G _Ic of the coatings. The fracture surfaces were examined using scanning electron microscope. On the basis of an idealized layer microstructure model for thermal sprayed coatings, the theoretical relationship between the cohesive fracture toughness and microstructure is proposed. The correlation between the calculated fracture toughness and observed value is examined. It was found that the fracture toughness of plasma sprayed Al₂O₃ coatings is not significantly influenced by spray distance up to 110 mm, and further increase in spray distance to 130 mm resulted in large decrease in the fracture toughness of the coatings. The G _Ic value predicted based on the proposed model using lamellar interface mean bonding ratio and the effective surface energy of bulk ceramics agreed well with the observed G _Ic data. Such agreement evidently shows that the fracture toughness of thermally sprayed ceramic coatings at the direction along coating surface is determined by lamellar interface bonding.