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1.
Plasma‐sprayed 8YSZ (zirconia stabilized with 8 wt% yttria)/NiCoCrAlYTa thermal barrier coatings (TBCs) were laser‐glazed using a continuous‐wave CO2 laser. Open pores within the coating surface were eliminated and an external densified layer was generated by laser‐glazing. The hot corrosion resistances of the plasma‐sprayed and laser‐glazed coatings were investigated. The two specimens were exposed for the same period of 100 h at 900 °C to a salt mixture of vanadium pentoxide (V2O5) and sodium sulfate (Na2SO4). Serious crack and spallation occurred in the as‐sprayed coating, while the as‐glazed coating exhibited good hot corrosion behavior and consequently achieved a prolonged lifetime. The results showed that the as‐sprayed 8YSZ coating achieved remarkably improved hot corrosion resistance by laser‐glazing. Changes in the coatings were studied by scanning electron microscopy (SEM) to observe the microstructure and X‐ray diffraction (XRD) technique to analyze the phase composition. XRD results showed that the reaction between yttria (Y2O3) and V2O5 produced yttrium vanadate (YVO4), leaching Y2O3 from YSZ and causing the progressive destabilization transformation from the tetragonal (t) to monoclinic (m) phase. The external dense layer produced by laser‐glazing restrained the penetration of the molten salt, to a certain extent, into the coating, which led to a relatively low m‐ZrO2 content in the coating after the hot corrosion test. Additionally, the segmented cracks in the coating surface induced by laser‐glazing were helpful to the improvement of strain tolerance of the coating. The two factors were important contributions to the significant enhancement of hot corrosion resistance of the as‐glazed YSZ coating. 相似文献
2.
The high‐temperature behavior of high‐purity, low‐density (HP‐LD) air plasma sprayed (APS) thermal barrier coatings (TBCs) with NiCoCrAlY bond coats deposited by argon‐shrouded plasma spraying is described. The high purity yttria‐stabilized zirconia resulted in top coats which are highly resistant to sintering and transformation from the metastable tetragonal phase to the equilibrium mixture of monoclinic and cubic phases. The thermal conductivity of the as‐processed TBC is low but increases during high temperature exposure even before densification occurs. The porous topcoat microstructure also resulted in good spallation resistance during thermal cycling. The actual failure mechanisms of the APS coatings were found to depend on topcoat thickness, topcoat density, and the thermal cycle frequency. The failure mechanisms are described and the durability of the HP‐LD coatings is compared with that of state‐of‐the‐art electron beam physical vapor deposition TBCs. 相似文献
3.
Hui Chen Yunfei Hao Hongying Wang Weijie Tang 《Journal of Thermal Spray Technology》2010,19(3):558-565
Nanostructured zirconia thermal barrier coatings (TBCs) have been prepared by atmospheric plasma spraying using the reconstituted
nanosized yttria partially stabilized zirconia powder. Field emission scanning electron microscope was applied to examine
the microstructure of the resulting TBCs. The results showed that the TBCs exhibited a unique, complex structure including
nonmelted or partially melted nanosized particles and columnar grains. A CO2 continuous wave laser beam has been applied to laser glaze the nanostructured zirconia TBCs. The effect of laser energy density
on the microstructure and thermal shock resistance of the as-glazed coatings has been systematically investigated. SEM observation
indicated that the microstructure of the as-glazed coatings was very different from the microstructure of the as-sprayed nanostructured
TBCs. It changed from single columnar grain to a combination of columnar grains in the fracture surface and equiaxed grains
on the surface with increasing laser energy density. Thermal shock resistance tests have showed that laser glazing can double
the lifetime of TBCs. The failure of the as-glazed coatings was mainly due to the thermal stress caused by the thermal expansion
coefficient mismatch between the ceramic coat and metallic substrate. 相似文献
4.
The failure mechanisms of thermal barrier coatings (TBCs) subjected to a thermal load are still not entirely understood. Thermal
stresses and/or oxidation cause the coating to fail and hence must be minimized. During the present investigation, TBCs up
to 1.0 mm were sprayed and withstood high thermal stresses during thermal testing. Owing to the substantial thickness, the
temperature at the top coat/bond coat interface was relatively low, resulting in a low oxidation rate. Furthermore, bond coats
were preoxidized before applying a top coat. The bond strength and the behavior during three different thermal loads of the
preoxidized TBCs were compared with a standard duplex TBC. Finite-element model (FEM) calculations that took account of bond
coat preoxidation and interface roughness were made to calculate the stresses occurring during thermal shock. It is concluded
that the thick TBCs applied during this research exhibit excellent thermal shock resistance and that a preoxidizing treatment
of the bond coat increases the lifetime during thermal loading, where oxidation is the main cause of failure. The FEM analysis
gives a first impression of the stress conditions on the interface undulations during thermal loading, but further development
is required. 相似文献
5.
稀土锆酸盐与8YSZ所组成的双陶瓷层涂层是目前热障涂层领域研究的热点,而陶瓷层厚度对其热冲击性能有着显著影响。采用有限元软件ANSYS研究了表层厚度对Sm2Zr2O7/8YSZ热障涂层淬冲击热应力的影响,并与单一Sm2Zr2O7涂层进行了比较。结果表明,在Sm2Zr2O7/8YSZ涂层的表面处具有最大的径向热冲击应力,最大轴向应力则存在于陶瓷层/金属粘结层界面处,涂层各处剪应力基本相当。涂层表面及两陶瓷层界面处的径向热应力随表层厚度的增加而减小,陶瓷层/粘结层界面处径向应力则随表层厚度增加而增大。每个界面处的轴向应力随表层厚度增加而降低,而剪应力绝对值则随表层厚度增加而增大。与单一Sm2Zr2O7涂层相比,Sm2Zr2O7/8YSZ涂层的热应力明显偏小,说明增加涂层的层数有利益改善涂层的抗热冲击性能。 相似文献
6.
CO2 continuous wave laser beam had been applied to the laser glazing of plasma sprayed nanostructure zirconia thermal barrier coatings. The effects of luser glazing processing parameters on the surface figuration and microstructure change had been carried out, the microstructure and phase composition of the coatings had been evaluated by the scanning electron microscope (SEM) and the X-ray diffraction (XRD). SEM observation indicates that the microstructure of the as-glazed coating could be altered from single columnar structure to a combination of the columnar grain and fine equiaxed grain with the different laser glazing conditions. XRD analysis illustrates that the predominance phase of the as-glazed coating is the metastable tetragonal phase, and the glazed coating with the single columnar structure has shown the clear orientation in (220) and (400) peaks while the other coatings do not show that. 相似文献
7.
Hsin Wang Ralph B. Dinwiddie Wallace D. Porter 《Journal of Thermal Spray Technology》2010,19(5):879-883
Thermal diffusivities of air plasma sprayed (APS) thermal barrier coatings (TBCs) were measured by the laser flash method.
The data were used to calculate thermal conductivity of TBCs when provided with density and specific heat data. Due to the
complicated microstructure and other processing-related parameters, thermal diffusivity of TBCs can vary as much as three-
to four-fold. Data collected from over 200 free-standing ZrO2-7-8wt.%Y2O3 TBCs are presented. The large database gives a clear picture of the expected “band” of thermal diffusivity values. When this
band is used as a reference for thermal diffusivity of a specific TBC, the thermal transport property of the TBC can be more
precisely described. This database is intended to serve researchers and manufacturers of TBCs as a valuable resource for the
evaluation of TBCs. 相似文献
8.
A. Scrivani G. Rizzi U. Bardi C. Giolli M. Muniz Miranda S. Ciattini A. Fossati F. Borgioli 《Journal of Thermal Spray Technology》2007,16(5-6):816-821
High-temperature thermal fatigue causes the failure of thermal barrier coating (TBC) systems. This paper addresses the development
of thick TBCs, focusing on the microstructure and the porosity of the yttria partially stabilized zirconia (YPSZ) coating,
regarding its resistance to thermal fatigue. Thick TBCs, with different porosity levels, were produced by means of a CoNiCrAlY
bond coat and YPSZ top coat, both had been sprayed by air plasma spray. The thermal fatigue resistance of new TBC systems
and the evolution of the coatings before and after thermal cycling was then evaluated. The limit of thermal fatigue resistance
increases depending on the amount of porosity in the top coat. Raman analysis shows that the compressive in-plane stress increases
in the TBC systems after thermal cycling, nevertheless the increasing rate has a trend which is contrary to the porosity level
of top coat.
This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been
expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain
Montavon, Ed., ASM International, Materials Park, OH, 2007. 相似文献
9.
Xiaolong Chen Yu Zhao Lijian Gu Binglin Zou Ying Wang Xueqiang Cao 《Corrosion Science》2011,(6):2335-2343
Hot corrosion studies of thermal barrier coatings (TBCs) with different YSZ/LaMgAl11O19 (LaMA) composite coating top coats were conducted in 50 wt.% Na2SO4 + 50 wt.% V2O5 molten salt at 950 °C for 60 h. Results indicate that TBCs with composite coating top coats exhibit superior oxidation and hot corrosion resistances to the TBC with the traditional YSZ top coat, especially for which has a LaMA overlay. The presence of LaMA can effectively restrain the destabilization of YSZ at the expense of its own partial degradation. The hot corrosion mechanism of LaMA coating and the composite coatings have been explored. 相似文献
10.
The current development of new generation gamma titanium aluminides is expected to result in alloy chemistries and microstructures capable of operating at temperatures in excess of 850 °C. Under these conditions, environmental and thermal protection becomes a concern since oxidation might eventually limit the maximum service temperatures achievable. Therefore protective coatings are necessary to exploit the full potential of gamma titanium aluminides at moderately elevated temperatures; however, as yet no coating system tested has proven sufficient performance for long‐term use in automotive and aerospace applications. Thermal barrier coatings (TBCs), typically applied to nickel‐based alloys, offer the potential to increase the service temperature of components by lowering the metal surface temperature in combination with cooling systems. The paper is focussed on development of thermal barrier coatings for gamma titanium aluminides. Different coatings were used for oxidation protection and bond coat application. Substrate specimens were either pre‐oxidized or coated with PVD‐Al2O3, TiAlCrYN, or diffusion aluminides. Yttria‐stabilized zirconia TBCs were deposited applying electron‐beam physical vapour deposition. Cyclic and quasi‐isothermal oxidation tests were carried out at 900 °C in air. Post‐oxidation analysis of the coating systems was performed using scanning electron microscopy with energy‐dispersive X‐ray spectroscopy. Zirconia top coats offer a promising thermal protection concept to be applied on γ‐TiAl components. However, high oxidation resistance has to be supplied by protective coatings. Diffusion layers of the TiAl3 aluminide provided excellent environmental protection because of the formation of a continuous alumina scale. No spallation of the thermal barrier coatings was observed on aluminized specimens during 1000 1‐h cycles and 3000 h of cyclic and isothermal oxidation testing, respectively. 相似文献
11.
This study examined the effects of application parameters for plasma spraying and CCh- laser glazing of two types of chromium-base
coatings. Coatings were deposited by low-pressure and atmospheric plasma spraying. The high-temperature corrosion resistance
of Cr-Ni-2.5Mo-lSi-0.5B (55 and 58% Cr) coatings was evaluated with respect to structural and compositional changes both in
the as- sprayed condition and after CCb- laser glazing. Coatings that were deposited by atmospheric plasma spraying and subsequently
laser glazed showed excellent resistance to oxidation and sulfate- vanadate attack at 900 °C due to the formation of a protective
chromia film and a high silica concentration on the top layers of the oxide. 相似文献
12.
Influence of heat treatment on nanocrystalline zirconia powder and plasma-sprayed thermal barrier coatings 总被引:1,自引:0,他引:1
Nanostructured zirconia top coat was deposited by air plasma spray and NiCoCrAlTaY bond coat was deposited on Ni substrate by low pressure plasma spray.Nanostructured and conventional thermal barrier coatings were heat-treated at temperature varying from 1050 to 1 250oC for 2-20 h.The results show that obvious grain growth was found in both nanostructured and conventional thermal barrier coatings(TBCs)after high temperature heat treatment.Monoclinic/tetragonal phases were transformed into cubic phase in the agglomerated nano-powder after calcination.The cubic phase content increased with increasing calcination temperature.Calcination of the powder made the yttria distributed on the surface of the nanocrystalline particles dissolve in zirconia when grains grew.Different from the phase constituent of the as-sprayed conventional TBC which consisted of diffusionlesstransformed tetragonal,the as-sprayed nanostructured TBC consisted of cubic phase. 相似文献
13.
Xiaolong Chen Yu Zhao Xizhi FanYangjia Liu Binglin ZouYing Wang Hongmei MaXueqiang Cao 《Surface & coatings technology》2011,205(10):3293-3300
New LaMgAl11O19 (LaMA)/YSZ double ceramic top coat thermal barrier coatings (TBCs) with the potential application in advanced gas-turbines and diesel engines to realize improved efficiency and durability were prepared by plasma spraying, and their thermal cycling failure were investigated. The microstructure evolutions as well as the crystal chemistry characteristics of LaMA coating which seemed to have strong influences on the thermal cycling failure of LaMA and the new double ceramic top coat TBCs based on LaMA/YSZ system were studied. For double ceramic top coat TBC system, interface modification of LaMA/YSZ by preparing thin composite coatings seemed to be more preferred due to the formations of multiple cracks during thermal cycling making the TBC to be more strain tolerant and as well as resulting in an improved thermal cycling property. The effects of the TGO stresses on the failure behavior of the TBCs were discussed through fluorescence piezo-spectroscopy analysis. 相似文献
14.
Dongming Zhu James A. Nesbitt Charles A. Barrett Terry R. McCue Robert A. Miller 《Journal of Thermal Spray Technology》2004,13(1):84-92
Ceramic thermal barrier coatings (TBCs) will play an increasingly important role in advanced gas turbine engines due to their
ability to further increase engine operating temperatures and reduce cooling, thus helping achieve future engine low emission,
high efficiency, and improved reliability goals. Advanced multicomponent zirconia (ZrO2)-based TBCs are being developed using an oxide defect clustering design approach to achieve the required coating low thermal
conductivity and high-temperature stability. Although the new composition coatings were not yet optimized for cyclic durability,
an initial durability screening of the candidate coating materials was conducted using conventional furnace cyclic oxidation
tests. In this paper, furnace cyclic oxidation behavior of plasma-sprayed ZrO2-based defect cluster TBCs was investigated at 1163°C using 45 min hot-time cycles. The ceramic coating failure mechanisms
were studied using scanning electron microscopy (SEM) combined with x-ray diffraction (XRD) phase analysis after the furnace
tests. The coating cyclic lifetime is also discussed in relation to coating processing, phase structures, dopant concentration,
and other thermo-physical properties. 相似文献
15.
Vakur Akdoğan Mehmet M. Dokur Gültekin Göller Özgül Keleş 《Journal of Materials Engineering and Performance》2013,22(9):2500-2509
Thermal barrier coatings (TBC) consisting of atmospheric plasma-sprayed ZrO2-8 wt.% Y2O3 and a high velocity oxygen fuel-sprayed metallic bond coat were subjected to CO2 continuous wave laser treatments. The effects of laser power on TBCs were investigated as was the thermally grown oxide (TGO) layer development of all as-sprayed and laser-treated coatings after thermal oxidation tests in air environment for 50, 100, and 200 h at 1100 °C. The effects of laser power on TBCs were investigated. TGO layer development was examined on all as-sprayed and laser-treated coatings after thermal oxidation tests in air environment for 50, 100, and 200 h at 1100 °C. Melted and heat-affected zone regions were observed in all the laser-treated samples. Oxidation tests showed a stable alumina layer and mixed spinel oxides in the TGO layers of the as-sprayed and laser-treated TBCs. 相似文献
16.
Kwang-Yong Park Yeon-Gil Jung In-Soo Kim Byung-Il Yang 《Journal of Thermal Spray Technology》2017,26(6):1161-1167
The thermal durability of thermal barrier coatings (TBCs) obtained using feedstock powders with different purity and phase content was investigated by cyclic thermal testing, including the effects on the sintering and phase transformation behaviors. Three kinds of 8 wt.% yttria-stabilized zirconia, namely regular purity (8YSZ), high purity (HP), and no monoclinic phase (nMP), were employed to prepare top coats by atmospheric plasma spraying on a NiCoCrAlY bond coat using a high-velocity oxy-fuel system. Use of 8YSZ, HP, and nMP for plasma spraying affected the microstructure and lifetime of the TBC in furnace cyclic testing (FCT) at 1100 °C and the sintering rate during annealing at 1400 °C for 50, 100, 200, and 400 h. In FCT, the TBC formed from nMP showed the longest durability, while that formed from HP showed lifetime performance similar to that obtained with regular-purity 8YSZ. The TBC obtained with nMP also exhibited the lowest monoclinic phase transition rate, followed by those obtained using HP and 8YSZ. 相似文献
17.
Properties of plasma-sprayed bond coats 总被引:1,自引:0,他引:1
W. J. Brindley 《Journal of Thermal Spray Technology》1997,6(1):85-90
Increasing bond coat oxidation resistance has been clearly linked to increasing durability of the ceramic layer of thermal
barrier coatings (TBCs). However, recent studies have shown that significant differences in TBC life can be achieved for different
bond coats that exhibit little or no difference in oxidation behav-ior. These data suggest that bond coat properties other
than oxidation resistance can also influence TBC life. Determination of which properties affect TBC life and how they do so
could be valuable in designing new, more durable TBCs. This paper reviews the results of comparative studies of the properties
of three bond coat compositions that have similar oxidation behavior but different TBC lives. An analysis of the properties
indicates that the thermal cycle residual stress, calculated from the coefficient of thermal ex-pansion and the stress relaxation
behavior of the three alloys, is strongly correlated to the observed dif-ferences in TBC life. 相似文献
18.
To improve the corrosion resistance and to study the effect of yttrium in the behavior of coatings produced by thermal spraying MCrAlY (M=Ni, Co) powders, CO2 laser processing was conducted. Three methods were used: (1) a combination of gas flame and plasma spraying in air followed by laser glazing in argon, (2) low-pressure plasma spraying (LPPS) and laser glazing in argon, and (3) LPPS and laser-gas (O2) alloying. Laser glazing in argon of the MCrAlY coatings sprayed in air promoted formation of weakly adherent agglomerates of Al–Y oxides and an alumina-chromia solid solution. Glazing in argon atmosphere of LPPS CoNiCrAlY and NiCrAlY coatings caused the formation of nickel aluminides besides the formation of Y–Al compounds. Gas (O2)-alloying of these coatings produces continuous and adherent (yttrium-containing) alumina and chromia layers. The effects of yttrium on the characteristics of the oxides formed in the coatings during laser glazing, laser-gas alloying, and high-temperature oxidation is discussed. This work also investigated the oxidation resistance of the laser-processed MCrAlY coatings in air and in the presence of 85 mol/o V2O5–Na2SO4 fused salt at 900°C. 相似文献
19.
Toshifumi KUBOHORI Toru ITO Wahidullah WAHI Yasuyuki INUI Toshiro IKUTA 《中国有色金属学会会刊》2009,19(4):984-987
Thermal spraying technique is widely used in various mechanical parts as a surface reforming technique. However, as demand to maintain superior mechanical performance in harsh operating environment increases, the need for non-destructive evaluation method for thermal spray coating becomes more important. For this purpose, we thinned the thickness of the thermal sprayed coating by abrasion with blasting and used ultrasonic inspection by means of bottom echo reflection for effective measurement of abrasion quantity in thermal sprayed coating. The results obtained are summarized as follows. When the thickness of thermal sprayed coating becomes thin, the echo height increases. This is because thermal sprayed coatings absorb ultrasonic energy. Ultrasonic energy absorbed by Al2O3 is smaller compared with Fe-13Cr coating. Thermal sprayed coatings submerged in water have a lower echo height compared with air. As mentioned above, the thermal sprayed coating thickness can be estimated using ultrasonic inspection by means of bottom echo back reflection. 相似文献