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1.
The influence of nucleation on the microstructure and properties of CVD Al2O3 was investigated. The experimental α-Al2O3 layers were deposited (a) without nucleation control and (b) with nucleation steps resulting in pronounced , and growth textures. The experimental layers were characterised using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Wear properties of the textured coatings were evaluated in turning. The chemistry of the nucleation surface appeared to be an important factor in pre-determining the phase content and growth textures of the Al2O3 layers. Optimised nucleation resulted in substantially improved wear properties and these kinds of α-Al2O3 layers were typically composed of relatively small, defect-free grains exhibiting no porosity. The textured α-Al2O3 layer showed the best wear resistance. 相似文献
2.
Cagri Tekmen Yoshiki Tsunekawa Masahiro Okumiya 《Surface & coatings technology》2008,202(17):4170-4175
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
3.
以La2O3粉、Al粉、CuO粉为反应物原料、纯铜为基体,采用原位合成技术和近熔点铸造法制备颗粒增强Cu基复合材料,研究La2O3对Al-CuO体系制备的Cu基复合材料组织及性能的影响。结果表明:添加La2O3可获得纳米Al2O3颗粒,且弥散分布于Cu基体中,制备的材料组织更加细小、均匀,其材料的电导率及摩擦磨损性能明显提高。当添加0.6%wtLa2O3,复合材料的电导率达到90.2%IACS,磨损量达到最小,相比未添加La2O3,其导电率提高10.1%,磨损量减小36.6%。 相似文献
4.
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
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.
Qiuyuan Feng Tingju Li Zhongtao Zhang Jian Zhang Mei Liu Junze Jin 《Surface & coatings technology》2007,201(14):6247-6252
Ni/Al2O3 composite coatings were prepared by a novel method from a modified Watt's type electrolyte containing nano-Al2O3 particles, where a high magnetic field was imposed in the direction parallel to an electrolytic current instead of mechanical agitation. Effects of magnetic field on the content of particles, surface morphology, microhardness and wear resistance of plating layer were investigated. It was found that the high magnetic field played an important role in the formation of composite coatings. The amounts of nano-Al2O3 particles in the composite coating increased with increasing of magnetic flux density and reached a maximum value at 8 T, then reduced slightly. The microhardness and wear resistance of the nanocomposite coatings also enhanced with increasing of magnetic flux density as compared to that of pure Ni coating fabricated in the absence of magnetic field. That was because the co-deposited nano-Al2O3 particles were uniformly distributed in the Ni matrix and contributed to greatly increase the microhardness and wear resistance of the composite coatings. Moreover, the mechanism of action of high magnetic field was discussed preliminarily. 相似文献
7.
The air oxidation characteristics of Fe3Al-4%Cr-(0, 0.5, 1, 2%)Mo alloys at 1000°C were studied using TGA, XRD, EPMA, and TEM/EDS. Molybdenum increased the oxidation
resistance of Fe3Al-4%Cr alloys. The whole Al2O3 grains that formed on the alloy surface contained a small amount of dissolved Fe ions. The Al2O3 grains next to the oxide-matrix interface additionally contained a small amount of dissolved Cr and Mo ions. Beneath the
thin but non adherent Al2O3 layer, an Al-depleted, Fe-enriched matrix zone formed due to the consumption of Al in the scale. 相似文献
8.
Md Ershadul AlamSamson Han Quy Bau NguyenAbdel Magid Salem Hamouda Manoj Gupta 《Journal of Alloys and Compounds》2011,509(34):8522-8529
In the present study, 1 and 2 wt.% of aluminum were successfully incorporated into magnesium based AZ31 alloy to develop new AZ41 and AZ51 alloys using the technique of disintegrated melt deposition. AZ41-Al2O3 and AZ51-Al2O3 nanocomposites were also successfully synthesized through the simultaneous addition of aluminum (1 and 2 wt.%, respectively) and 1.5 vol.% nano-sized alumina into AZ31 magnesium following same route. Alloy and composite samples were then subsequently hot extruded at 400 °C and characterized. Microstructural characterization studies revealed equiaxed grain structure, reasonably uniform distribution of particulate and intermetallics in the matrix and minimal porosity. Physical properties characterization revealed that addition of both aluminum and nano-sized alumina reduced the coefficient of thermal expansion of monolithic AZ31. The presence of both Al and nano-sized Al2O3 particles also assisted in improving overall mechanical properties including microhardness, engineering and specific tensile strengths, ductility and work of fracture. The results suggest that these alloys and nanocomposites have significant potential in diverse engineering applications when compared to magnesium AZ31 alloy. 相似文献
9.
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
10.
This paper investigates the interfacial structure in hot-wall CVD TiN/κ-Al2O3 multilayer coatings using both HREM and DFT modeling. Two multilayers with different thicknesses of the TiN layers (50 and 600 nm) separating the κ-Al2O3 layers are analyzed. The general microstructure of the two multilayers is relatively similar. The TiN layer in the thicker TiN/κ-Al2O3 coating is thick enough to be several TiN grains high. This means that epitaxial columns, which are often found in the thinner TiN/κ-Al2O3 coatings, are not present. However, the orientation relationships at the TiN/κ-Al2O3 interfaces are the same in both multilayers. The HREM investigations show that κ-Al2O3 (001) planes can grow directly on flat (111) TiN faces, without any other phases or detectable amounts of impurities, such as sulphur, present. Where the TiN layers are more curved, γ-Al2O3 can be grown, at least partly stabilized by the cube-on-cube orientation relationship between γ-Al2O3 and the underlying TiN. The DFT calculations show very similar adsorption strengths for an O monolayer positioned on Ti-terminated TiC(111) and TiN(111) surfaces, with preferred adsorption in the fcc site. O adsorption on N-terminated TiN(111) is much weaker, with preferred adsorption in the top site. Calculated elastic-energy contributions yield a higher stability for κ-Al2O3 on TiN(111) than on TiC(111) and a higher stability for κ-Al2O3 than for α-Al2O3 on both TiC and TiN. This indicates that the observed higher stability of κ-Al2O3 on TiC(111) than on TiN(111) is not due to the lattice mismatch, while the preferred epitaxial growth of κ-Al2O3 over α-Al2O3 can be partly attributed to the mismatch. 相似文献
11.
Nano-sized Al2O3 ceramic particles (50 nm) were co-deposited with nickel using electrodeposition technique to develop composite coatings. The coatings were produced in an aqueous nickel bath at different current densities and the research investigated the effect of applied current on microstructure and thickness of the coatings. The variation in some mechanical properties such as hardness, wear resistance, and the adhesive strength of the composite coatings is influenced by the applied current and this was also studied. The morphology of the coatings was characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. The hardness, wear resistance, and bond strength of the coatings were evaluated by Vickers micro-hardness test, pin-on-disc test, and tensile test, respectively. Results showed that the Al2O3 particles were uniformly distributed in the coatings, and the coatings deposited at a current density of 0.01 A/cm2 was most favorable in achieving a maximum current efficiency which causes the co-deposition of a maximum amount of Al2O3 particles (4.3 wt.%) in the coatings. The increase in Al2O3 particles in the coatings increased the mechanical properties of the Ni-Al2O3 composite coatings by grain refining and dispersion strengthening mechanisms. 相似文献
12.
X.H Wang 《Corrosion Science》2003,45(5):891-907
The isothermal oxidation behavior of bulk Ti3AlC2 has been investigated at 1000-1400 °C in air for exposure times up to 20 h by means of TGA, XRD, SEM and EDS. It has been demonstrated that Ti3AlC2 has excellent oxidation resistance. The oxidation of Ti3AlC2 generally followed a parabolic rate law with parabolic rate constants, kp that increased from 4.1×10−11 to 1.7×10−8 kg2 m−4 s−1 as the temperature increased from 1000 to 1400 °C. The scales formed at temperatures below 1300 °C were dense, adherent, resistant to cyclic oxidation and layered. The inner layer of these scales formed at temperatures below 1300 °C was continuous α-Al2O3. The outer layer changed from rutile TiO2 at temperatures below 1200 °C to a mixture of Al2TiO5 and TiO2 at 1300 °C. In the samples oxidized at 1400 °C, the scale consisted of a mixture of Al2TiO5 and, predominantly, α-Al2O3, while the adhesion of the scales to the substrates was less than that at the lower temperatures. Effect of carbon monoxide at scale/substrate was involved in the formation of the continuous Al2O3 layers. 相似文献
13.
采用氩弧熔覆的方法,以Ni60A自熔性合金粉末为粘结相,添加Ti粉、C粉和不同含量的稀土氧化物Y2O3,在16Mn钢基体上制备出TiC陶瓷颗粒增强金属基熔覆涂层. 运用XRD, SEM等手段对复合涂层的显微组织进行表征和分析,并对熔覆涂层的硬度及耐磨性进行了测试. 结果表明,适量添加Y2O3可以使涂层组织中枝晶的方向性减弱、同时细化涂层组织,使涂层组织更加均匀,涂层的硬度和耐磨性有显著提高. 添加2% Y2O3熔覆涂层的组织为最细,涂层具有较高的显微硬度和良好的耐磨性能. 相似文献
14.
采用磁控溅射在Al2O3陶瓷表面沉积了Ti+Nb/Mo金属层,实现了氧化铝陶瓷的金属化,并通过电镀镍提高了金属化效果.采用AgCu28钎料,实现了金属化Al2O3陶瓷与Kovar合金的可靠连接.通过扫描电子显微镜和能谱观察了钎缝的微观组织.结果表明,钎料与母材发生了明显的界面反应.Cu元素扩散进入Kovar合金,同时Ni元素扩散进入钎料的富铜区,从而促进AgCu/Kovar连接界面的形成;金属化层在Al2O3/AgCu钎料界面处,起到了关键作用,其中铌可以抑制脆性化合物形成,缓解残余应力.金属化层镀镍后,钎缝中AgCu共晶区明显,且钎缝较宽,对提高镀镍试样的钎焊接头强度有一定作用. 相似文献
15.
Mechanical properties and wear rates of Al2O3-13 wt.% TiO2 (AT-13) and Al2O3-43 wt.% TiO2 (AT-43) coatings obtained by flame and atmospheric plasma spraying were studied. The feed stock was either ceramic cords or powders. Results show that the wear resistance of AT-13 coatings is higher than that of AT-43 and it seems that the effect of hardness on wear resistance is more important than that of toughness. Additionally, it was established that, according to conditions used to elaborate coatings and the sliding tribological test chosen, spray processes do not seem to have an important effect on the wear resistance of these coatings. 相似文献
16.
Effects of plasma spraying conditions on wear resistance of nanostructured Al2O3-8 wt.%TiO2 coatings plasma-sprayed with nanopowders were investigated in this study. Five kinds of nanostructured coatings were plasma-sprayed on a low-carbon steel substrate by varying critical plasma spray parameter (CPSP) and spray distance. The coatings consisted of fully melted region of γ-Al2O3 and partially melted region, and the fraction of the partially melted regions and pores decreased with increasing CPSP or decreasing spray distance. The hardness and wear test results revealed that the hardness of the coatings increased with increasing CPSP or decreasing spray distance, and that the hardness increase generally led to the increase in wear resistance, although the hardness and wear resistance were not correlated in the coating fabricated with the low CPSP. The main wear mechanism was a delamination one in the coatings, but an abrasive wear mode also appeared in the coating fabricated with the low CPSP. According to these wear mechanisms, the improvement of wear resistance in the coating fabricated with the low CPSP could be explained because the improved resistance to fracture due to the presence of partially melted regions might compensate a deleterious effect of the hardness decrease. 相似文献
17.
Anwar Ul-Hamid 《Corrosion Science》2004,46(1):27-36
In the present study the isothermal oxidation behaviours of Ni-10Cr-5Al, Ni-20Cr-5Al and Ni-30Cr-5Al alloys were investigated. The alloys were oxidised in air for 50 h at 1000 °C. Analytical transmission electron microscopy was used to characterize the morphology, structure and composition of the oxide scale. The oxide formed adjacent to the alloy was α-Al2O3 such that the higher was the Cr content of the alloy the easier was its formation. The Ni-30Cr-5Al alloy formed a complete layer of α-Al2O3 in the initial stages of oxidation through ‘oxygen gettering’ by Cr. A decrease in scale thickness and an increase in scale adherence were observed with an increase in Cr content from 10 to 30 wt.%. 相似文献
18.
Yibin Li Yue Sun Wenzhu Zhang Yujie Ding Xiaodong He 《Journal of Alloys and Compounds》2008,460(1-2):115-119
Nanocrystalline aluminum embedded in amorphous dielectric alumina matrix thin films (nc-Al/α-Al2O3) was synthesized via reactive magnetron sputtering. The nc-Al/α-Al2O3 films at different oxygen partial pressures were sputtered on p-type Si substrates from a pure Al target in the mixed ambient of Ar and O2. Both deposition rate and aluminum concentration increase as the oxygen partial pressure decreases. X-ray photoelectron spectroscopy and high-resolution transmission electron microscope studies give the confirmation of nanocrystalline Al embedded in amorphous Al2O3 matrix. This nanocomposite thin film exhibits memory effect as a result of charge trapping. The flat band voltage value depends on the Al nanocrystal concentration which is related to oxygen partial pressure. 相似文献
19.
A. Daoud M. T. Abou El-Khair A. N. Abdel-Azim 《Journal of Materials Engineering and Performance》2004,13(2):135-143
Aluminum (Al) alloy 7075 reinforced with Al2O3 particles was prepared using the stir casting method. The microstructure of the cast composites showed some degree of porosity
and sites of Al2O3 particle clustering, especially at high-volume fractions of Al2O3 particles. Different squeeze pressures (25 and 50 MPa) were applied to the cast composite during solidification to reduce
porosity and particle clusters. Microstructure examinations of the squeeze cast composites showed remarkable grain refining
compared with that of the matrix alloy. As the volume fraction of particles and applied squeeze pressure increased, the hardness
linearly increased. This increase was related to the modified structure and the decrease in the porosity. The effect of particle
volume fraction and squeeze pressure on the dry-sliding wear of the composites was studied. Experiments were performed at
10, 30, and 50 N with a sliding speed of 1 m/s using a pin-on-ring apparatus. Increasing the particle volume fraction and
squeeze pressure improved the wear resistance of the composite compared with that of the monolithic alloy, because the Al2O3 particles acted as load-bearing constituents. Also, these results can be attributed to the fact that the application of squeeze
pressure during solidification led to a reduction in the porosity, and an increase in the solidification rate, leading to
a finer structure. Moreover, the application of squeeze pressure improved the interface strength between the matrix and Al2O3 particles by elimination of the porosity at the interface, thereby providing better mechanical locking. 相似文献
20.
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