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1.
Failure of components due to high temperature oxidation is the major degradation mechanism in boiler and gas turbine industries. Superalloys having superior mechanical properties and creep resistance are used in these applications but lack resistance to oxidation under aggressive environments. Protective coatings are used to improve their oxidation resistance in such applications. In the present investigation, Al2O3–40%TiO2 coating was deposited on superni 718 and superni 601 superalloys by low velocity oxy fuel process. The as sprayed coating was characterised for microhardness, surface roughness, scanning electron microscopy and X-ray diffraction analysis. High temperature oxidation behaviour of Al2O3–40%TiO2 coated and uncoated superni 718 and superni 601 superalloys has been evaluated at the elevated temperatures of 800 and 900°C for total duration of 50 cycles under cyclic conditions. Each cycle consisted of keeping the samples for 1 h at the elevated temperature followed by 20 min cooling in ambient air. Al2O3–40TiO2 coating in the as sprayed condition showed the presence of Al2O3–TiO2, α-Al2O3, TiO2 as the main phases. Al2O3–40%TiO2 coating on superni 718 and superni 601 superalloys has shown a lower oxidation rate as compared to those of uncoated superalloys. However, the oxidation rate of the coating was not steady due to the occurrence of spallation/sputtering at various stages. The coating was found adherent on the substrate superalloys throughout the study.  相似文献   

2.
This paper reports a study of how the choice of plasma spray parameters, used during deposition of Al2O3-13%TiO2 coatings on carbon steel, influences the cavitation erosion properties of such coatings. The parameters studied are the power feeding rate and hydrogen flow rate. The surface and cross section of coatings before and after cavitation were also observed by scanning electron microscopy (SEM). The phases present in the coatings were characterized by X-ray diffraction method (XRD). The microscopic observations were used to study the inter-lamellar connection, porosity, unmelted particles and so on inside the coating. We also measured the roughness, microhardness, adhesion strength and cavitation erosion of the coatings. The XRD results showed that the coating includes different allotropes of Al2O3 such as α and γ. The cavitation erosion studies of the coatings were conducted by ultrasonic cavitation testing on the basis of ASTM G32 standard. It was found that cavitation erosion is accelerated around the unmelted particles and porosities. The results reveal that the cavitation resistance of the coating is determined by its microstructure and that increasing discontinuities (inside the coating) reduce its cavitation resistance. We have found that the coating obtained at hydrogen gas flow rate of 16 L/min and powder feeding rate of 20 g/min has the best cavitation resistance.  相似文献   

3.
Al + SiC, Al + Al2O3 composites as well as pure Al, SiC, and Al2O3 coatings were prepared on Si substrates by the cold gas dynamic spray process (CGDS or cold spray). The powder composition of metal (Al) and ceramic (SiC, Al2O3) was varied into 1:1 and 10:1 wt.%, respectively. The propellant gas was air heated up to 330 °C and the gas pressure was fixed at 0.7 MPa. SiC and Al2O3 have been successfully sprayed producing coatings with more than 50 μm in thickness with the incorporation of Al as a binder. Also, hard ceramic particles showed peening effects on the coating surfaces. In the case of pure Al metal coating, there was no crater formation on hard Si substrates. However, when Al mixed with SiC and Al2O3, craters were observed and their quantities and sizes depended on the composition, aggregation and size of raw materials.  相似文献   

4.
Crystalline PVD Al2O3 coatings offer great potential for their use in cutting operations. They promise high hot hardness and high oxidation resistance at elevated temperatures. Alumina exists in different crystallographic phases. α-Al2O3 appears to be the only thermodynamically stable phase at all common temperatures and pressures. Today there are many efforts to generate α-Al2O3 by means of physical vapour deposition. In this regard one problem is the high deposition temperature, which does not allow the deposition on temperature-sensitive materials.Another promising candidate is γ-Al2O3 which is more fine-grained than α-Al2O3 and can be deposited at lower temperatures. At high temperatures γ-Al2O3 might be transformed into α-Al2O3, which could limit the application temperature. But until now it is not clearly proved, up to which temperatures γ-Al2O3 thin films are stable and which mechanisms influence the stability. In the present work different (Ti,Al)N/γ-Al2O3 coatings are deposited on cemented carbides by means of Magnetron Sputter Ion Plating (MSIP). The (Ti,Al)N bond coat was employed to improve adhesion of γ-Al2O3 on the substrate. It could be shown that the γ-phase is stable in vacuum up to 1200 °C. In the atmosphere the formation of α-Al2O3 begins at 900 °C and it is influenced by the choice of transition zone between the (Ti,Al)N interlayer and γ-Al2O3. The results show that the thermal stability of the γ-phase and therefore the application temperature of the coating can be enhanced by the choice of interlayer.  相似文献   

5.
Al2O3, Al2O3-Cr2O3 and Cr2O3 coatings were deposited by atmospheric plasma spraying. Phase composition of powders and as-sprayed coatings was determined by X-ray diffraction. Electron probe microanalyzer was employed to investigate the polished and fractured surface morphologies of the coatings. Mechanical properties including microhardness, fracture toughness and bending strength were evaluated. The results indicate that the addition of Cr2O3 is conducive to the stabilization of α-Al2O3. Compared with the pure Al2O3 and Cr2O3 coatings, Al2O3-Cr2O3 composite coatings show lower porosities and denser structures. Heterogeneous nucleation of α-Al2O3 occurs over the isostructural Cr2O3 lamellae and partial solid solution of Al2O3 and Cr2O3 might be occurring as well. Furthermore, grain refining and solid solution strengthening facilitate the mechanical property enhancement of Al2O3-Cr2O3 composite coatings.  相似文献   

6.
Graphite is one of the candidate materials proposed for application in pyrochemical reprocessing plants involving aggressive molten chloride environment. Post treatments are promising techniques for the improvement of properties of thermal spray coatings for different industrial applications. In the present work, the effect of post treatments like vacuum annealing (VA) and laser melting (LM) on the microstructure and chemical modification of plasma sprayed Al2O3-40 wt.% TiO2 coatings over high density (HD) graphite substrates has been investigated. When compared with sprayed coatings (SC), VA coatings showed cluster morphology and LM coatings exhibited homogenous microstructure. On laser melted surfaces networks of cracks were observed. XRD studies showed that the metastable γ-Al2O3 phase present in the SC is transformed to stable α-Al2O3 after post treatments. In LM coatings Al2TiO5 phase was more predominant in contrast to SC and VA coatings. The microhardness enhancement was observed in case of LM coating compared to the VA and SC. Due to elimination of coating defects in LM samples, there is a considerable reduction in the surface roughness.  相似文献   

7.
Novel YSZ (6 wt.% yttria partially stabilized zirconia)-(Al2O3/YAG) (alumina-yttrium aluminum garnet, Y3Al5O12) double-layer ceramic coatings were fabricated using the composite sol-gel and pressure filtration microwave sintering (PFMS) technologies. The thin Al2O3/YAG layer had good adherence with substrate and thick YSZ top layer, which presented the structure of micro-sized YAG particles embedded in nano-sized α-Al2O3 film. Cyclic oxidation tests at 1000 °C indicated that they possessed superior properties to resist oxidation of alloy and improve the spallation resistance. The thermal insulation capability tests at 1000 °C and 1100 °C indicate that the 250 μm coating had better thermal barrier effect than that of the 150 μm coating at different cooling gas rates. These beneficial effects should be mainly attributed to that, the oxidation rate of thermal grown oxides (TGO) scale is decreased by the “sealing effect” of α-Al2O3, the “reactive element effect”, and the reduced thermal stresses by means of nano/micro composite structure. This double-layer coating can be considered as a promising TBC.  相似文献   

8.
In-situ plasma spraying (IPS) is a promising process to fabricate composite coatings with in-situ formed thermodynamically stable phases. In the present study, mechanically alloyed Al-12Si, B2O3 and TiO2 powder was deposited onto an aluminum substrate using atmospheric plasma spraying (APS). It has been observed that, during the coating process, TiB2 and Al2O3 are in-situ formed through the reaction between starting powders and finely dispersed in hypereutectic Al-Si matrix alloy. Also, obtained results demonstrate that in-situ reaction intensity strongly depends on spray conditions.  相似文献   

9.
为了提高热障涂层(TBC)的抗沉积物(主要成分为CaO、MgO、Al2O3和SiO2,简称CMAS)腐蚀性能,采用磁过滤阴极真空电弧(FCVA)技术在TBC表面上制备了致密的Al2O3覆盖层,比较和分析了Al2O3改性TBC和沉积态TBC的润湿行为和抗CMAS腐蚀性能。结果表明:使用FCVA技术制备Al2O3覆盖层的过程对7%(质量分数)氧化钇稳定的氧化锆(7YSZ)相的结构无明显影响,且经Al2O3改性的TBC综合性能均优于沉积态TBC。在1250 ℃、CMAS腐蚀条件下,Al2O3覆盖层有效地限制了熔融CMAS在TBC表面上的扩散行为。同时,Al2O3填充了7YSZ柱状晶之间的间隔并且阻碍了熔融CMAS的渗透,证明了FCVA可作为一种制备Al2O3涂层的新方法以提高TBC的抗CMAS腐蚀性能,且Al2O3涂层及其制备过程对TBC的热震性能均无消极影响。  相似文献   

10.
过渡材料对等离子喷涂Al2O3梯度陶瓷涂层性能影响   总被引:1,自引:0,他引:1       下载免费PDF全文
针对Al2O3陶瓷涂层结合强度低、孔隙率高的实际,选择NiAl金属间化合物和金属铜粉作为过渡材料,利用等离子喷涂制备Al2O3梯度陶瓷涂层,并对梯度涂层进行组织形貌观察,测试结合强度和孔隙率.结果表明,梯度涂层的组织表现出宏观的不均匀性和微观连续性的分布特征,NiAl和Cu是金属基体与Al2O3涂层之间过渡层的理想材料,可以有效地提高涂层的结合强度,而Cu-Al2O3梯度涂层又比NiAl-Al2O3梯度涂层结合强度高;梯度涂层的孔隙率远低于双涂层的孔隙率,在Cu-Al2O3梯度涂层中随Al2O3含量的增加,涂层的孔隙率降低,而且孔隙率低于NiAl-Al2O3梯度涂层.  相似文献   

11.
NiAl-TiB2 composite coatings with 0, 10 and 20 wt.% TiB2 were synthesized on the Ni-based superalloy substrate using electro-thermal explosion ultrahigh speed spraying technology. The microstructure analysis shows that the coatings consist of submicron grains. The bond between coatings and substrate is metallic cohesion. TiB2 as a powerful reinforcement is doped in NiAl for increasing its hardness. The isothermal oxidation test is carried out for the composite coatings at 1100 °C in air. The result shows that the oxidation resistance of NiAl coating is higher than that of NiAl-10TiB2 and NiAl-20TiB2 coatings. The phases of oxides on the coatings during the process at high temperature have been analyzed by X-ray diffraction. The results show that Al2O3 and Cr2O3 coexistence on surface of NiAl coating, while Al2O3, Cr2O3, TiO2 and a small amount of NiO form on surface of NiAl-10TiB2 and NiAl-20TiB2 coatings after oxidation for 4 h.  相似文献   

12.
张哲  严刚  倪福松  贾明子 《表面技术》2014,43(2):18-23,54
目的研究Al2O3纳米粒子环氧复合涂层对钢筋的防护性能。方法制备Al2O3纳米粒子,将其添加至环氧涂料中,并涂覆在工业钢筋表面成膜。通过XRD和SEM对Al2O3进行表征;利用电化学噪声、交流阻抗谱分析技术,对复合涂层在3.5%(质量分数)NaCl介质中对工业钢筋的防护性能进行测试分析。结果制备的氧化铝纳米粒子的粒径平均为75 nm。通过对电化学噪声测试的有效数据进行时域和频域分析,通过交流阻抗谱分析及数据拟合,认为Al2O3纳米粒子添加量为0.1%(以占环氧树脂质量的百分比计)时,涂层对钢筋的防护性能最好。结论向环氧涂层中添加适量的Al2O3纳米粒子,可以明显提升其对钢筋的防护性能。  相似文献   

13.
Air plasma sprayed TBCs usually include lamellar structure with high interconnected porosities which transfer oxygen from YSZ layer towards bond coat and cause TGO growth and internal oxidation of bond coat.The growth of thermally grown oxide (TGO) at the interface of bond coat and ceramic layer and internal oxidation of bond coat are considered as the main destructive factors in thermal barrier coatings.Oxidation phenomena of two types of plasma sprayed TBC were evaluated: (a) usual YSZ (yttria stabilized zirconia), (b) layer composite of (YSZ/Al2O3) which Al2O3 is as a top coat over YSZ coating. Oxidation tests were carried out on these coatings at 1100°C for 22, 42 and 100h. Microstructure studies by SEM demonstrated the growth of TGO underneath usual YSZ coating is higher than for YSZ/Al2O3 coating. Also cracking was observed in usual YSZ coating at the YSZ/bond coat interface. In addition severe internal oxidation of the bond coat occurred for usual YSZ coating and micro-XRD analysis revealed the formation of the oxides such as NiCr2O4, NiCrO3 and NiCrO4 which are accompanied with rapid volume increase, but internal oxidation of the bond coat for YSZ/Al2O3 coating was lower and the mentioned oxides were not detected.  相似文献   

14.
Alumina (Al2O3) coatings deposited by chemical vapor deposition (CVD) with different modifications and dopants are widely applied as wear resistant coatings on cemented carbide cutting tools. The aim of this work was to investigate the influence of CH4 addition on the deposition of α-Al2O3 by low-pressure chemical vapor deposition (LPCVD). The coatings were deposited at 1005 °C on a TiN–TiCN base layer using a precursor gas mixture of AlCl3, CH4, CO2, HCl, H2S, and H2. Coating characterization was conducted by scanning electron microscopy (SEM), glow discharge optical emission spectroscopy (GDOES), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), glancing angle X-ray diffraction (GAXRD), nanoindentation and tribological ball-on-disk tests against Al2O3 balls. Additionally, the ball-on-disk wear tracks were investigated by Raman spectroscopy.  相似文献   

15.
The detonation spraying is one of the most promising thermal spray variants for depositing wear and corrosion resistant coatings. The ceramic (Al2O3), metallic (Ni-20 wt%Cr) , and cermets (WC-12 wt%Co) powders that are commercially available were separated into coarser and finer size ranges with relatively narrow size distribution by employing centrifugal air classifier. The coatings were deposited using detonation spray technique. The effect of particle size and its distribution on the coating properties were examined. The surface roughness and porosity increased with increasing powder particle size for all the coatings consistently. The feedstock size was also found to influence the phase composition of Al2O3 and WC-Co coatings; however does not influence the phase composition of Ni-Cr coatings. The associated phase change and %porosity of the coatings imparted considerable variation in the coating hardness, fracture toughness, and wear properties. The fine and narrow size range WC-Co coating exhibited superior wear resistance. The coarse and narrow size distribution Al2O3 coating exhibited better performance under abrasion and sliding wear modes however under erosion wear mode the as-received Al2O3 coating exhibited better performance. In the case of metallic (Ni-Cr) coatings, the coatings deposited using coarser powder exhibited marginally lower-wear rate under abrasion and sliding wear modes. However, under erosion wear mode, the coating deposited using finer particle size exhibited considerably lower-wear rate.  相似文献   

16.
Al2O3-13%TiO2 coatings were deposited on stainless steel substrates from conventional and nanostructured powders using atmospheric plasma spraying (APS). A complete characterization of the feedstock confirmed its nanostructured nature. Coating microstructures and phase compositions were characterized using SEM, TEM, and XRD techniques. The microstructure comprised two clearly differentiated regions. One region, completely fused, consisted mainly of nanometer-sized grains of γ-Al2O3 with dissolved Ti+4. The other region, partly fused, retained the microstructure of the starting powder and was principally made up of submicrometer-sized grains of α-Al2O3, as confirmed by TEM. Coating microhardness as well as tribological behavior were determined. Vickers microhardness values of conventional coatings were in average slightly lower than the values for nanostructured coating. The wear resistance of conventional coatings was shown to be lower than that of nanostructured coatings as a consequence of Ti segregation. A correlation between the final properties, the coating microstructure, and the feedstock characteristics is given.  相似文献   

17.
Reactive plasma spraying (RPS) is a promising technology for in situ formation of aluminum nitride (AlN) coatings. Recently, AlN-based coatings were fabricated by RPS of alumina (Al2O3) powder in N2/H2 thermal plasma. This study investigated the feasibility of RPS of a fine Al2O3/AlN mixture and the influence of the plasma gases (N2, H2) on the nitriding conversion, and coating microstructure and properties. Thick AlN/Al2O3 coatings with high nitride content were successfully fabricated. The coatings consist of h-AlN, c-AlN, Al5O6N, γ-Al2O3, and a small amount of α-Al2O3. Use of fine particles enhanced the nitriding conversion and the melting tendency by increasing the surface area. Furthermore, the AlN additive improved the AlN content in the coatings. Increasing the N2 gas flow rate improved the nitride content and complete crystal growth to the h-AlN phase, and enhanced the coating thickness. On the other hand, though the H2 gas is required for plasma nitriding of the Al2O3 particles, increasing its flow rate decreased the nitride content and the coating thickness. Remarkable influence of the plasma gases on the coating composition, microstructure, and properties was observed during RPS of the fine particles.  相似文献   

18.
In this work, Ni and Ni–Al2O3 nanocomposite coatings were applied on AZ91 magnesium alloy using a pulse plating process and the corrosion resistance of coated samples was evaluated by means of the potentiodynamic polarisation method in 3.5?wt-% NaCl solution. Field emission scanning electron microscopy was employed to identify microstructure and morphology of the coatings. Vickers microhardness and pin-on-disc wear tests were also used to investigate mechanical properties of the coatings. The polarisation test revealed that the pure Ni coating on AZ91 along with the presence of nanoparticles were key factors leading to a reduction in the corrosion current density and the improvement of corrosion resistance so that the corrosion current density of 210.45?µA?cm?2 for the substrate (AZ91) decreases to 31.92 and 1.54?µA?cm?2 by applying pure Ni and Ni–Al2O3 nanocomposite coatings, respectively. Furthermore, Ni–Al2O3 nanocomposite coating increased the microhardness and wear resistance compared to the substrate up to 435 and 340%, respectively.  相似文献   

19.
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。  相似文献   

20.
The conventional molybdenum alloys, lacking of hard particles enhancing wear property, have relative poor wear resistance though they are widely used in wear parts. To resolve the above question, Mo alloys reinforced by in-situ Al2O3 particles are developed using powder metallurgy method. The in-situ α-Al2O3 particles in molybdenum matrix are obtained by the decomposition of aluminum nitrate after liquid-solid incorporation of MoO2 and Al(NO3)3 aqueous solution. The α-Al2O3 particles well bonded with molybdenum distribute evenly in matrix of Mo alloys, which refine grains of alloys and increase hardness of alloys. The absolute density of alloy increases firstly and then decreases with the increase of Al2O3 content, while the relative density rises continuously. The friction coefficient of alloy, fluctuating around 0.5, is slightly influenced by Al2O3. However, the wear resistance of alloy obviously affected by the Al2O3 particles rises remarkably with the increasing of Al2O3 content. The Al2O3 particles can efficiently resist micro-cutting to protect molybdenum matrix, and therefore enhances the wear resistance of Mo alloy.  相似文献   

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