Microstructural features and properties of plasma sprayed YPSZ/NiCrAlY thermal barrier coating (TBC)

The plasma sprayed thermal barrier coating (TBC) consists of NiCrAlY bond coating and yttria partially stabilized zirconia (YPSZ) top coating. NiCrAlY coating mainly contains Ni solid solution with face centered cubic lattice, Al_2O_3 oxides and pores. The most obvious feature of YPSZ coating with tetragonal zirconia is a lot of vertical microcracks in this coating. The thermal insulation capability of the TBC increased with an increase in YPSZ coating thickness, the temperature drop across the TBC increasing from 60℃ to 92℃ with increasing YPSZ coating thickness from 100 μm to 500 μm. The thermal shock resistance of the TBC decreased with increasing YPSZ coating thickness and cracks initiated mainly in original vertical microcrack tips of the YPSZ coating and propagated not only along YPSZ coating/ NiCrAlY coating interface but also through NiCrAlY coating. The oxidation process of the TBC at 1 200℃ can be divided into two stages: transient oxidation stage with rapid oxidation rate and steady oxidation stage with slow oxidation. Their transition time was about 10 hours. The weight gain for 100 hours was 3.222 mg/mm2. It is favorable to increase YPSZ coating toughness and to decrease the pores and oxides of the TBC system for improving thermal shock resistance and oxidation resistance of the TBC.

Characterization of functionally graded ZrO_2 thermal barrier coatings sprayed by supersonic plasma spray with dual powder feed ports

The functionally graded thermal barrier coatings （FG-TBCs） with 80%ZrO2-13%CeO2-7%Y2O3 （C-YSZ）/NiCoCrAlY were prepared using a recently developed supersonic plasma spraying（S-PS） with dual powder feed ports system. The thermal shock experiment of FG-TBCs specimens was carried out by means of the automatic thermal cycle device, in which the samples were heated to 1200℃ by oxygen-acetylene flame jet then water-quenched to ambient temperature. The temperature—time curves of specimens and photographs can be watched on-line and recorded by a computer during the test. The results show that the totally 1mm-thick FG-TBCs have excellent thermal shock resistance due to the fact that the coatings have no any peeling-off after 200 thermal cycles. The microstructures and morphologies of FG-TBCs were characterized and analyzed by SEM.

Premature failure induced by non-equilibrium grain-boundary tantalum segregation in air-plasma sprayed ZrO_(2)-YO_(1.5)-TaO_(2.5)thermal barrier coatings

ZrO_(2)-YO_(1.5)-TaO_(2.5)(ZYTO)is a promising top-coat material for thermal barrier coatings(TBCs).The bulk properties of ZYTO have been reported by several studies,but its performances as TBCs are less-well understood.In this work,ZYTO TBCs were prepared by air plasma spraying(APS)and their thermal cycling performances were investigated at 1150℃.Despite of the good bulk properties,APS ZYTO TBCs present an extremely short thermal fatigue life.This is attributed to the non-equilibrium grain-boundary segregation of TaO_(2.5) induced by limited solubility and rapid quenching during APS process,resulting in a tetragonal(t)to cubic(c)and metastable-tetragonal(tm)phase transformation in ZYTO TBCs.The volume shrinkage(~0.74vol%)of phase transformation leads to many cracks at the c/tm phase boundaries after deposition.On the other hand,the formation of cubic phase with massive grain-boundary Ta segregation induces a large intergranular embrittlement and a weak bonding strength(~5.3 MPa),resulting in the premature failure of the ZYTO TBCs.

Rare earth effect on the microstructure and tribological properties of FeNiCr coatings

FeNiCr alloys with various amounts of La2O3 powders were thermally sprayed onto steel substrate.Electron probe microscopy analysis （EPMA）,X-ray photoelectron spectroscopy （XPS）,and an Optimol SRV oscillating friction and wear tester in a ball-on-disc contact configuration were employed to investigate the properties of the sprayed coatings.The results show that rare earth can refine the microstructure effectively and make the element distribution uniform,which leads to the improvement in the properties of the coatings.Meanwhile,the wear rate of the FeNiCr alloy with 1.5% La2O3 is smaller than those of the other coatings.Interestingly,the rare earth can reduce the friction coefficient and act as a self-lubricant in the oxide debris layer formed on the worn surface in friction.The wear mechanism of the coatings is oxidation wear,and a large amount of counterpart material is transferred to the coatings.

Effect of microstructure evolution and crystal structure on thermal properties for plasma-sprayed RE_(2)SiO_(5)(RE=Gd,Y,Er)environmental barrier coatings

In this work,the microstructure evolution,thermal expansion,thermal conductivity,and thermal shock resistance properties of the plasma-sprayed Xl-Gd_(2)SiO_(5),X2-Y_(2)SiO_(5),and X2-Er_(2)SiO_(5)coatings were evaluated and compared by experimental measurement and theoretical exploration.Results showed that significant microstructure evolution such as crystallization of amorphous phase,grain growth,and defects reduction was observed in the RE_(2)SiO_(5)coatings after thermal aging at 1400℃.The Xl-Gd_(2)SiO_(5)coating exhibited higher CTE values than the X2-Y_(2)SiO_(5)and X2-Er_(2)SiO_(5)coatings,which was related to their crystal structure.The thermal conductivity of thermal-aged RE_(2)SiO_(5)coating was much higher than that of the as-sprayed RE_(2)SiO_(5)coating,and thermal conductivity was determined not only by crystal structure but also mainly by the microstructure of the coatings.The X2-Y_(2)SiO_(5)and X2-Er_(2)SiO_(5)coatings with lower thermal mismatch stre s ses presented much better thermal shock resistance than the X1-Gd_(2)SiO_(5)coating.

Microstructure characteristics of coating with amorphous phases prepared from Fe-based alloy powders by plasma spray

In this paper, alloy powders mixed with a molar ratio of Fe ： P ： C of 80 ： 13 ： 7 were sprayed on Q235 steel by plasma spray method to prepare coating with amorphous phases. The phase composition of the mixed alloy powders and prepared coating were characterized by X-ray diffraction （ XRD ）. The morphology and the composition cf the coating were analyzed by scanning eleetron microscopy （SEM） nnd energy dispersive apectroscopy （ EDS ）. In addition, the thermal stability ef the coating with amorphous phases was characterized by differential thermal analyzer （ DTA ）. Tile results showed that, usirtg mixed alloy powders with a molar ratio of Fe： P： C of 80：13：7, the coating containing certain amount of amorphous alloys was suceessathlly prepared through atmospheric plasma spray technique. In the coating, the main phases were determined to be Fe, FeP aad Fe2P. The crystallization of the coating started from about 461°. Tile coating was mechanically adhered to the substrate.

Plasma spray-physical vapor deposition toward advanced thermal barrier coatings:a review

Plasma spray–physical vapor deposition(PS–PVD)is a unique technology that enables highly tailorable functional films and coatings with various rare metal elements to be processed.This technology bridges the gap between conventional thermal spray and vapor deposition and provides a variety of coating microstructures composed of vapor,liquid,and solid deposition units.The PS–PVD technique serves a broad range of applications in the fields of thermal barrier coatings(TBCs),environmental barrier coatings(EBCs),oxygen permeable films,and electrode films.It also represents the development direction of high-performance TBC/EBC preparation technologies.With the PS–PVD technique,the composition of the deposition unit determines the microstructure of the coating and its performance.When coating materials are injected into a nozzle and transported into the plasma jet,the deposition unit generated by a coating material is affected by the plasma jet characteristics.However,there is no direct in situ measurement method of material transfer and deposition processes in the PS–PVD plasma jet,because of the extreme conditions of PS–PVD such as a low operating pressure of*100 Pa,temperatures of thousands of degrees,and a thin and high-velocity jet.Despite the difficulties,the transport and transformation behaviors of the deposition units were also researched by optical emission spectroscopy,observation of the coating microstructure and other methods.This paper reviews the progress of PS–PVD technologies considering the preparation of advanced thermal barrier coatings from the perspective of the transport and transformation behaviors of the deposition units.The development prospects of new high-performance TBCs using the PS–PVD technique are also discussed.

Microstructures and Properties of NiCrBSi/WC Biomimetic Coatings Prepared by Plasma Spray Welding

The NiCrBSi/WC biomimetic coatings were prepared on the low carbon steel substrate by plasma spray welding with mixed powders （WC-Col2＋NiCrBSi） based on the bionic principles, and the coating characteristics were investigated. The results indicate that the coatings have a full metallurgical bond in coating/substrate interface, and consist mainly ofy-Ni, WC, Cr23C6, Cr7C3, Ni3Si, CrsB3, and FeNi3 phases. The powder composition influences the microstructures and properties of the coatings. The WC content and the hardness of coatings increase with the mass fraction of WC-Co 12 powder. The biomimetic coatings have much higher wear resistance compared with the low carbon steel, which is attributed to the combination of hard WC and chromium carbide particles （bionic units） and soft y-Ni matrix in the coatings. It is favorable to prepare the biomimetic coating by plasma spray welding with the mixed powders （20wt%WC-Col2＋80wt%NiCrBSi） for improving the wear resis- tance of the coating.

Overview on the Development of Nanostructured Thermal Barrier Coatings

Thermal barrier coatings （TBCs） have successfully been used in gas turbine engines for increasing operation temperature and improving engine efficiency. Over the past thirty years, a variety of TBC materials and TBC deposition techniques have been developed. Recently, nanostructured TBCs emerge with the potential of commercial applications in various industries. In this paper, TBC materials and TBC deposition techniques such as air plasma spray （APS）, electron beam physical vapor deposition （EB-PVD）, laser assisted chemical vapor deposition （LACVD） are briefly reviewed. Nanostructured 7-8 wt pct yttria stabilized zirconia （7-8YSZ）TBC by air plasma spraying of powder and new TBC with novel structure deposited by solution precursor plasma spray （SPPS） are compared. Plasma spray conditions, coating forming mechanisms, microstructures,phase compositions, thermal conductivities, and thermal cycling lives of the APS nanostructured TBC and the SPPS nanostructured TBC are discussed. Research opportunities and challenges of nanostructured TBCs deposited by air plasma spray are prospected.

Effects of Layer Thickness and Edge Conditions to Thermoelastic Characteristics on Thermal Barrier Coatings

The thermoelastic behaviors of such as temperature distribution, displacements, and stresses in thermal barrier coatings (TBC) are seriously influenced by top coat thickness and edge conditions. The top coat of TBC specimens prepared with TriplexPro?-200 system was controlled by changing the processing parameter and feedstock, showing the various thicknesses and microstructures. A couple of governing partial differential equations were derived based on the thermoelastic theory. Since the governing equations were too involved to solve analytically, a finite volume method was developed to obtain approximations. The thermoelastic behaviors of TBC specimens with the various thicknesses and microstructures were estimated through mathematical approaches with different edge conditions. The results demonstrated that the microstructure and thickness of the top coat, and the edge condition in theoretical analysis were crucial factors to be considered in controlling the thermoelastic characteristics of plasma-sprayed TBCs.

Microstructure studies of air-plasma-spray-deposited CoNiCrAlY coatings before and after thermal cyclic loading for high-temperature application

In the present study, bond-coats for thermal barrier coatings were deposited via air plasma spraying（APS） techniques onto Inconel 800 and Hastelloy C-276 alloy substrates. Scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, X-ray diffraction（XRD）, and atomic force microscopy（AFM） were used to investigate the phases and microstructure of the as-sprayed, APS-deposited Co Ni Cr Al Y bond-coatings. The aim of this work was to study the suitability of the bond-coat materials for high temperature applications. Confirmation of nanoscale grains of the γ/γ′-phase was obtained by TEM, high-resolution TEM, and AFM. We concluded that these changes result from the plastic deformation of the bond-coat during the deposition, resulting in Co Ni Cr Al Y bond-coatings with excellent thermal cyclic resistance suitable for use in high-temperature applications. Cyclic oxidative stability was observed to also depend on the underlying metallic alloy substrate.

Investigation on plasma-sprayed ZrO_2 thermal barrier coating on nickel alloy substrate

The thermal barrier coatings with NiCrAlY alloy bonding layer, NiCrAlY Y 2O 3 stabilized ZrO 2 transition layer and Y 2O 3 stabilized ZrO 2 ceramic layer are prepared on nickel alloy substrates using the plasma spray technique. The relationship among the composition, structure and property of the coatings are investiga ted by means of optical microscope, scanning electronic microscope and the experiments of thermal shock resistance cycling and high temperature oxidation resistance. The results show that the structure design of introdu cing a transition layer between Ni alloy substrate and ZrO 2 ceramic coating guarantees the high quality and properties of the coatings; ZrO 2 coatings doped with a little SiO 2 possesses better thermal shock resistance and more excellent hot corrosion resistance as compared with ZrO 2 coating materials without SiO 2 ;the improvement in performance of ZrO 2 coating doped with SiO 2 is due to forming more dense coating structure by self closing effects of the flaws and pores in the ZrO 2 coatings.

Microstructure modification of Y2O3 stabilized ZrO2 thermal barrier coatings by laser glazing and the effects on the hot corrosion resistance

Y2O3 stabilized ZrO2(YSZ)thermal barrier coatings(TBCs)are prone to hot corrosion by molten salts.In this study,the microstructure of atmospheric plasma spraying YSZ TBCs is modified by laser glazing in order to improve the corrosion resistance.By optimizing the laser parameters,a^18μm smooth glazed layer with some vertical cracks was produced on the coating surfaces.The as-sprayed and modified coatings were both exposed to hot corrosion tests at 700 and 1000℃for 4 h in V2O5 molten salt,and the results revealed that the modified one had improved corrosion resistance.After hot corrosion,the glazed layer kept structural integrity,with little evidence of dissolution.However,the vertical cracks in the glazed layer acted as the paths for molten salt penetration,accelerating the corrosion of the non-modified coating.Further optimization of the glazed layer is needed in the future work.

Influence of HfO2 alloying effect on microstructure and thermal conductivity of HoTaO4 ceramics

HfO2 alloying effect has been applied to optimize thermal insulation performance of HoTaO4 ceramics.X-ray diffraction,Raman spectroscopy,and X-ray photoelectron spectroscopy are employed to decide the crystal structure.Scanning electronic microscopy is utilized to detect the influence of HfO2 alloying effect on microstructure.Current paper indicates that the same numbers of Ta5+and Ho3+ions of HoTaO4 are substituted by Hf4+cations,and it is defined as alloying effect.No crystal structural transition is introduced by HfO2 alloying effect,and circular pores are produced in HoTaO4.HfO2 alloying effect is efficient in decreasing thermal conductivity of HoTaO4 and it is contributed to the differences of ionic radius and atomic weight between Hf4+ions and host cations(Ta5+and Ho3+).The least experimental thermal conductivity is 0.8 W·K–1·m–1 at 900℃,which is detected in 6 and 9 mol%-HfO2 HoTaO4 ceramics.The results imply that HfO2–HoTaO4 ceramics are promising thermal barrier coatings(TBCs)due to their extraordinary thermal insulation performance.

Sc_(2)O_(3)和Y_(2)O_(3)复合掺杂ZrO_(2)热障涂层陶瓷材料的组织结构与力学性能

质量分数为7±1%氧化钇部分稳定氧化锆(7YSZ)是广泛应用的热障涂层陶瓷材料。然而,其在1200℃以上长期服役存在相稳定性差、烧结加剧和力学性能下降等弊端。因此,本工作提出新型Sc_(2)O_(3)-Y_(2)O_(3)协同掺杂ZrO_(2)热障涂层陶瓷材料,采用固相合成法制备了摩尔分数为7.5%Sc_(2)O_(3)-x%Y_(2)O_(3)-(92.5-x)%ZrO_(2)(x=0,0.1,0.2,0.3)陶瓷。通过X射线衍射仪(XRD)、场发射扫描电镜(SEM)等手段,重点探究Y_(2)O_(3)掺杂含量对高温固相合成陶瓷材料的微观组织结构演变行为以及维氏硬度、断裂韧性、弹性模量和三点抗弯强度等力学性能的影响规律。结果表明:Sc_(2)O_(3)-Y_(2)O_(3)复合掺杂ZrO_(2)陶瓷材料经1450℃×3.5 h高温烧结的致密度大于97%,主要由四方相结构组成,该材料的维氏硬度、弹性模量、断裂韧性和三点抗弯强度与传统8YSZ相当,分别为13~14 GPa,211~214 GPa,6.5~7.0 MPa·m^(1/2),520~850 MPa之间;断裂机制主要为穿晶断裂和沿晶断裂的混合方式,其中以穿晶断裂为主导。Sc_(2)O_(3)-Y_(2)O_(3)复合掺杂ZrO_(2)陶瓷可作为一种潜在的高温热障涂层陶瓷材料。

YZrHf热障涂层的制备及热震性能分析

目的研究喷涂态YZrHf热障涂层的微观组织及其抵抗高温热冲击的性能,探讨高温条件下热生长氧化物(TGO)对陶瓷层的影响。方法采用大气等离子喷涂(APS)技术制备厚度约为300μm的YZrHf热障涂层,并将涂层在950℃下保温15min后进行水冷循环热震实验,直至涂层剥落失效,使用SEM、EDS、X射线衍射仪对制备态及热震实验后的热障涂层微观组织进行分析。结果涂层表面粗糙不平且分布有十几到几十微米长度的网状裂纹,这些相互贯通的裂纹为氧气的进入提供了通道。经过101次循环热震实验后,涂层部分区域剥落失效,SEM结果显示,在陶瓷层/黏结层界面处、黏结层内部均出现了热生长氧化物,且在陶瓷层中分布有横向、纵向的贯通性裂纹,而在TGO生长区域,也出现了一些小裂纹,但涂层并未剥落。经测定分析可知,TGO的主要成分为Al_(2)O_(3)、Cr_(2)O_(3)、NiO以及尖晶石氧化物组成的混合物(CSN)。结论热震实验后TGO层中Al元素贫化,Ni、Cr等元素向界面处迁移参与反应,同时尖晶石氧化物以α-Al_(2)O_(3)为基础形成,这些氧化物的存在会产生对陶瓷层的压应力,加速涂层的开裂失效;涂层中掺杂的HfO2能够阻止Al的外扩散,降低氧化层的生长速率。

悬浮液等离子喷涂沉积热障涂层研究进展

悬浮液等离子喷涂(SPS)采用液相送料的方式,解决了纳米级粉末在热喷涂过程中送料困难的问题,同时,可沉积具有纳米级或亚微米级的柱状晶或垂直裂纹等结构的涂层。综述了近年SPS制备热障涂层的相关研究进展。对SPS的原理和工艺特点进行了介绍;阐明了SPS制备热障涂层典型微结构,包括垂直裂纹和柱状晶结构的沉积机理;探讨了悬浮液特性(包括固含量、黏度、表面张力)、喷涂工艺参数(包括喷枪类型、喷涂距离)、基材表面粗糙度等对SPS沉积涂层微结构、热物理性能、热循环性能等的影响。最后,对SPS未来的发展及研究趋势进行了展望。

氧化钇部分稳定氧化锆陶瓷涂层的高温耐久性辨析

氧化钇部分稳定的氧化锆(YSZ)作为热障涂层材料广泛应用于复杂高温工况,其优异的高温耐久性主要由不可相变介稳四方相(t′)所贡献。然而,目前对t′相可靠服役温度上限的界定较为模糊,主流观点仍停留在1200℃左右。基于此,采用大气等离子体喷涂(APS)工艺制备YSZ陶瓷涂层,经不同时效热处理,针对涂层微结构、相组成、烧结收缩和断裂韧性等变化进行分析研究。结果表明,经24 h@1400℃热处理附加7年室温存放后,陶瓷层未见单斜相;300 h@1400℃和300 h@1600℃热处理涂层中单斜相体积分数分别为3.55%和35.41%,且均未碎裂。300 h@1600℃涂层烧结线性收缩率为0.4%。高温时效热处理同时伴随晶粒生长和孔隙愈合,涂层抗折强度和断裂韧性随之增加,因而认为APS YSZ涂层可在1400℃下长时间(~300 h)服役。

热障涂层微-纳分级微观结构制备及其抗CMAS润湿性能

通过悬浮液等离子喷涂技术(SPS)在常规大气等离子(APS)热障涂层表面构建了具有微-纳双尺度的表面微观结构,比较了高温下熔融CMAS(Calcium-Magnesium-Alumina-Silicate)在两种涂层表面上的润湿行为差异,从实验和理论角度分析了表面微观结构差异对涂层抗CMAS润湿性能的影响。研究结果显示,得益于涂层表面微-纳分级微观结构,SPS涂层的抗CMAS润湿性能较常规APS涂层的抗CMAS润湿性能得到了显著提升。在1300℃下热处理5 min后,熔滴在SPS涂层上的润湿角为115.1°,而熔融CMAS在常规APS涂层的润湿角为52.1°;热处理10 min后,熔融CMAS在SPS涂层上的润湿角为68.2°,是常规APS涂层上润湿角的3.2倍。此外,SPS涂层疏松多孔的微观结构特征有利于空气的储存,在熔体润湿涂层表面过程中可起到支撑液滴的作用。

等离子喷涂工艺参数对BSAS基可磨耗环境障涂层组织性能影响

为满足陶瓷基复合材料表面可磨耗环境障一体化涂层的需求,采用大气等离子喷涂技术制备BSAS+聚酯(BSAS+P)涂层,研究喷涂工艺参数对涂层组织性能的影响。结果表明:涂层为典型的层状结构,内部存在一定数量的孔洞和微裂纹;在一定范围内,提高喷涂电流、氢气流量和载气流量,有利于提高粉末颗粒熔化程度,使其在基体表面平铺变形效果好,所得涂层具有合适的孔隙率和表面硬度。等离子喷涂BSAS+P涂层最佳工艺参数为:喷涂电流550A、氩气流量40NLPM、氢气流量10NLPM、载气流量2.5NLPM,得到涂层孔隙率为13.7%,表面硬度为64.7HR45Y。采用上述工艺参数制得的涂层,与基体结合强度较高,并且在1000℃下与Si3N4球间的平均摩擦系数为1.2,具有较好的可磨耗性能。