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1.
In this study, the effects of bond coat on the properties of Al2O3 and Al2O3–13 wt.% TiO2 coatings, which is plasma sprayed onto a commercial pure titanium substrate with and without Ni–5 wt.% Al (METCO 450 NS) as bond coating layer were investigated in terms of microhardness, bonding strength and surface roughness. Optical and scanning electron microscopy (SEM) examinations revealed that there is a uniform coating layer with no spalling and delamination. However, there is a little amount of porosity. The results indicated that the application of bond coat layer in the plasma spraying of Al2O3 and Al2O3–13 wt.% TiO2 on pure titanium substrate has increased the hardness and bonding strength of coatings. While the adhesive bonding is dominant without bond coat, the cohesive bonding is dominant with the application of the bond coating layer. It has been observed that percentage of cohesion strength was about three times higher than that of adhesion strength.  相似文献   

2.
Al2O3, SiC and kaolin were employed as additives in combustion synthesizing Al2O3–TiB2 ceramic composite. Effects of the additives on adiabatic temperature, combustion wave velocity, volume change and composite density were studied, and bending strength of the synthesized ceramics was evaluated. By theoretical calculation, the adiabatic temperature of Al–TiO2–H3BO3 system is 2314.85 °C and decreases with increasing the additive addition. With Al2O3 addition, the phases presented in the ceramic composite are unchanged, and the phases of SiC and 3Al2O3·2SiO2 emerges when SiC and kaolin are added. The addition of the additives results in a refined TiB2 particulate size and reduces combustion wave velocity. The highest density is achieved with the addition of kaolin from 10 to 30 wt.% making the volume change from ?4.6 to ?1.2%. The bending strength of the TiB2–Al2O3 composite is improved eight times with the addition of 30 wt.% kaolin.  相似文献   

3.
《Ceramics International》2016,42(7):8525-8530
Composite TiAlCo powders (TiO2, Co3O4 and Al2O3) were synthesized by spray–drying technology. The phase composition and morphology of synthesized powders were characterized by X-ray diffraction and scanning electron microscopy, respectively. Using above synthesized powders as starting materials, TiAlCo ceramic were successfully prepared by atmospheric plasma spraying (APS) with an internally fed powder torch. Electromagnetic parameters and microwave absorption properties of the prepared ceramic coatings were investigated in the frequency range from 8.2 to 12.4 GHz (X-band). It was found that both the real part and imaginary part of dielectric constant decreases with increasing Al2O3 content in the whole measured frequency region. Dielectric properties are closely related to the relaxation polarization and interfacial polarization and electric conductivity. Furthermore, by combination of the frequency selective surfaces (FSS) and prepared coatings, a double absorption band of the reflection loss spectra had been observed in X-band. The optimized reflection loss values exceeding −10 dB can be obtained in the frequency range of X-band when the coating thickness is only 1.8 mm, and the reflection loss is insensitive to incident angle from 0° to 45° for both transverse electromagnetic (TE) and transverse magnetic (TM) polarizations.  相似文献   

4.
《Ceramics International》2016,42(12):13659-13663
Magnesium and its alloys are the engineering materials which have the potential ability to be able to used widely particularly in the automotive, aerospace and in the biomedical sectors, especially thanks to their features such as lightness, specific strength that they have and biocompatibility. However, due to their poor wear resistance and corrosion resistance, the areas of usage are being restricted. This situation prevents Mg alloys to be used without any surface protection despite their good mechanical properties such as high strength/weight ratio. In this study, plasma spraying method is used to improve the poor corrosion resistance of AZ31 Mg alloy. Al2O3–13 wt% TiO2 (AT13) and Al2O3–40 wt% TiO2 (AT40) composite ceramic coatings were coated successfully on the surfaces of AZ31 Mg samples. The wear properties of the AT13 and AT40 coated samples were investigated for tribological applications. Surface morphology and microstructure of the duplex treated samples were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The microhardness value of the uncoated AZ31 Mg alloy is 40±3 HV0.1, while the microhardness values of the AT40 and AT13 coatings are enhanced to 800±39 HV0.1 and 1500±35 HV0.1, respectively.  相似文献   

5.
In the present work, Al2O3–20 wt%Al2TiO5 composite was prepared from reaction sintering of alumina and titania nanopowders. The nano-sized raw powders were reconstituted into nanostructured particles by ball milling. Then, the nanostructured reconstituted powders were pressed and pressureless-sintered into bulk ceramics at 1300, 1400, 1500 °C for 2 h. The phase composition and microstructures of reconstituted powders and as-prepared ceramic composites were characterized by using X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope and energy-dispersive spectrometer (EDS). The microstructural analysis of the ceramic showed that the average grain size of the alumina–aluminium titanate composite increases with increasing the temperature. Also, SEM proved the existence of a proper interface between Al2TiO5 and Al2O3 grains and preferential distribution of aluminium titanate particles in the grain boundaries. XRD analysis indicated the absence of rutile titania in the sintered composite ensuring complete formation of aluminium titanate. The hardness of the samples sintered at 1300, 1400, 1500 °C were 4.8, 6.2 and 8.5 GPa, respectively.  相似文献   

6.
Al2O3/Al2O3 ceramic matrix composites (CMC) are candidate materials for hot-gas leading components of gas turbines. Since Al2O3/Al2O3 CMC are prone to hot-corrosion in combustion environments, the development of environmental barrier coatings (EBC) is mandatory. Owing to its favorable chemical stability and thermal properties, Y2O3 is considered a candidate EBC material for Al2O3/Al2O3 CMC. Up to 1 mm thick Y2O3 coatings were deposited by means of air plasma spraying (APS) on Al2O3/Al2O3 CMC with a reaction-bonded Al2O3 bond-coat (RBAO). APS Y2O3 coatings exhibit a good adherence in the as-deposited state as well as upon isothermal annealing up to 1400 °C. Moreover, furnace cyclic testing performed at 1200 °C revealed an excellent durability. This is explained by the formation of a continuous, approximately 1 μm thick reaction zone at the APS Y2O3/RBAO interface. The reaction zone between Y2O3 and Al2O3 comprises three layers of thermodynamically stable yttrium-aluminates exhibiting strong bonding, respectively.  相似文献   

7.
《Ceramics International》2016,42(12):14107-14112
Stabilized Al2TiO5 (AT)-mullite (M) porous ceramics were fabricated by starch consolidation casting using corn starch as curing agent and their microstructure, mechanical properties, pore size distribution and corrosion resistance were examined. Results showed that AT-M porous ceramic with the flexural strength of 11.5 MPa, apparent porosity of about 54.7% and pore size distribution in the range of 1–15 µm could be obtained with 10 wt% corn starch addition. Corrosion resistance results showed mass losses in hot H2SO4 solution and NaOH solution for 10 h to decreased from 1.03% to 0.36% and 4.39–2% when the calcination temperature increased from 1400 °C to 1450 °C, which proved these AT-M porous ceramics to possess an excellent corrosion resistance in acidic condition when calcined at 1450 °C.  相似文献   

8.
Recently, nano bio-composites have emerged as an efficient strategy to upgrade the structural and functional properties of synthetic bone grafts. Bioinert ceramics have attracted wide attention because of their biocompatibility. Novel composites of nano-hydroxyapatite/GEL with incorporation of bioinert ceramics like Al2O3, TiO2 and ZrO2 for different composites as a reinforcing phase to increase its mechanical properties was prepared. The nHAp with the size of 10–50 nm in diameter and 50–100 nm in length was uniformly distributed into GEL matrix to form the composite. It was found that the composite with a high ceramic content has good homogeneity and mechanical strength, which are close to the cancellous bone. An interconnected porous material with porosity of at least 74% was achieved by phase inversion method. The formation reaction of the nHAp/GEL/bioinert ceramic nanocomposite was then investigated via FT-IR, XRD, TG/DTA and SEM. The organic–inorganic interaction between HAp nano crystallites and GEL molecules were confirmed from FT-IR and TG/DTA. The compressive strength of bioinert ceramic reinforced nanocomposites scaffolds could high up to 13.15 MPa while those of nHAp/GEL were 4.87 MPa. The nano indentation technique was used to find nano hardness and fracture toughness was evaluated by Vickers indentation.  相似文献   

9.
《Ceramics International》2017,43(15):12126-12137
Mechanical resistance of Al2O3 + TiO2 nanocomposite ceramic coating deposited by electrostatic spray deposition method onto X10CrAlSi18 steel to thermal and slurry tests was investigated. The coating was produced from colloidal suspension of TiO2 nanoparticles dispersed in 3 wt% solution of Al2(NO3)3, as Al2O3 precursor, in ethanol. TiO2 nanoparticles of two sizes, 15 nm and 32 nm, were used in the experiments. After deposition, coatings were annealed at various temperatures, 300, 1000 and 1200 °C, and next exposed to cyclic thermal and slurry tests. Regardless of annealing temperature and the size of TiO2 nanoparticles, the outer layer of all coatings was porous. The first five thermal cycles caused a rapid increase of aluminum content of the surface layer to 30–37 wt%, but further increase in the number of thermal cycles did not affect the aluminum content. The oxidation rate of coating-substrate system was lower during the thermal tests than during annealing. The oxidation rate was also lower for smaller TiO2 particles (15 nm) forming the coating than for the larger ones (32 nm). The protective properties of Al2O3 + TiO2 coating against intense oxidation of substrate were lost at 1200 °C. Slurry tests showed that coatings annealed at 1000 °C had the best slurry resistance, but thermal tests had weakened this slurry resistance, mainly due to decreasing adhesion of the coating.  相似文献   

10.
Thermal spraying using liquid feedstock has emerged as a promising technology for the deposition of finely structured ceramic coatings. In order to provide a comparative assessment of the deposition mechanisms occurring when spraying suspension or solution feedstock, suspensions of 300 nm-sized ZrO2–4.5 mol.% Y2O3 particles dispersed in water and in ethanol and solutions of zirconium and yttrium salts, corresponding to ZrO2–4.5 mol.% Y2O3 and ZrO2–8 mol.% Y2O3 stoichiometries, were processed by plasma spraying using different parameter settings. In-flight diagnostics of sprayed droplets, together with the morphological, microstructural and phase analysis of individual lamellae collected onto polished substrates, performed by SEM, FIB, AFM and micro-Raman spectroscopy, led to the identification of deposition mechanisms, which were subsequently verified through the characterisation of complete coating layers.  相似文献   

11.
《Ceramics International》2016,42(15):16640-16643
Transparent Y2O3 ceramics were fabricated by the solid-state reaction and vacuum sintering method using La2O3, ZrO2 and Al2O3 as sintering aids. The microstructure of the Y2O3 ceramics sintered from 1550 °C to 1800 °C for 8 h were analyzed by SEM. The sintering process of the Y2O3 transparent ceramics was optimized. The results showed that when the samples were sintered at 1800 °C for 8 h under vacuum, the average grain sizes of the ceramics were about 3.5 µm. Furthermore, the transmittance of Y2O3 ceramic sintered at 1800 °C for 8 h was 82.1% at the wavelength around the 1100 nm (1 mm thickness), which was close to its theoretical value. Moreover, the refractive index of the Y2O3 transparent ceramic in the temperature range from 30 °C to 400 °C were measured by the spectroscopic ellipsometry method.  相似文献   

12.
We report on how the mechanical properties of sintered ceramics (i.e., a random mixture of equiaxed grains) with the Al2O3–Y2O3–ZrO2 eutectic composition compare with those of rapidly or directionally solidified Al2O3–Y2O3–ZrO2 eutectic melts. Ceramic microcomposites with the Al2O3–Y2O3–ZrO2 eutectic composition were fabricated by sintering in air at 1400–1500 °C, or hot pressing at 1300–1400 °C. Fully dense, three phase composites of Al2O3, Y2O3-stabilized ZrO2 and YAG with grain sizes ranging from 0.4 to 0.8 μm were obtained. The grain size of the three phases was controlled by the size of the initial powders. Annealing at 1500 °C for 96 h resulted in grain sizes of 0.5–1.8 μm. The finest scale microcomposite had a maximum hardness of 19 GPa and a four-point bend strength of 282 MPa. The fracture toughness, as determined by Vickers indentation and indented four-point bending methods, ranged from 2.3 to 4.7 MPa m1/2. Although strengths and fracture toughnesses are lower than some directionally or rapidly solidified eutectic composites, the intergranular fracture patterns in the sintered ceramic suggest that ceramic microcomposites have the potential to be tailored to yield stronger, tougher composites that may be comparable with melt solidified eutectic composites.  相似文献   

13.
《Ceramics International》2016,42(8):9599-9604
Ti/Mo bilayer thin films were deposited onto Al2O3 ceramic by magnetron sputtering with a subsequent high temperature sintering to ensure the robust brazing of Al2O3 ceramic to Kovar (Fe–Ni–Co) alloy. The interface reaction process between Ti film and Al2O3 ceramic as well as the joining strength between metallized Al2O3 ceramic and Kovar alloy were investigated systematically using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, transmission electron microscopy, and electronic universal testing machine. The results show that the active Ti film can react with Al2O3 ceramic to form Ti3Al and TiO during high-temperature sintering process, in which the amount, size and morphology of TiO crucially depend on the sintering temperature. As the sintering temperature reaches 1200 °C, a plenty of spherical TiO nanoparticles with ~ 150 nm in diameter and metallic nature can be created across the Ti/Al2O3 interfaces, which can effectively act as ‘bridges’ to join Ti film to Al2O3 substrate firmly. Hence, the optimal joining strength of 69.6±3.1 MPa between metallized Al2O3 ceramic and Kovar alloy can be obtained, much better than those counterparts metallized at 900 °C and 1050 °C almost without the existence of observable TiO.  相似文献   

14.
The effects of plasma gas composition on the bond-strength of HA/Ti composite coatings were investigated. HA/Ti composite coatings were deposited on titanium substrates by a radio-frequency (rf) thermal plasma spraying method with input powers of 10–30 kW. The ratio of the HA and Ti powders supplied into the plasma was precisely controlled by two microfeeders so as to change the coating's composition from Ti-rich at the bottom to HA-rich at its upper layer. The bond (tensile) strength of the obtained HA/Ti composite coatings was 40–65 MPa when sprayed with plasma gas containing N2 (i.e., Ar–N2). On the other hand, HA/Ti composite coatings prepared with plasma gas containing O2 (i.e., Ar–O2) had significantly lower bond strength (under 30 MPa). XRD patterns of Ti coatings without HA showed that titanium nitride and titanium dioxide formed, respectively, on titanium deposits sprayed with Ar–N2 and Ar–O2 plasma. Scanning electron microscopic (SEM) observation showed an acicular texture on the Ti deposits prepared with Ar–N2 plasma. SEM observations implied that, when sprayed with Ar–O2 plasma, a thin TiO2 layer formed at the interfaces between the Ti splats in the deposits.  相似文献   

15.
(3Ni + Fe)–Al2O3 and Ni3Fe–Al2O3 composites were constructed using Ni, Fe and Ni3Fe powders (μm), recovered from metallic waste (ferrous scrap) by a hydrometallurgical process, along with a 0–35 wt.% of commercial α-Al2O3 powder (0–55 vol.% theoretically). Established PM fabrication processes were applied. The successfully prepared metal–ceramics were characterized, and measurements of their physico-mechanical properties were conducted. The composite microstructures exhibit a residual porosity varying with the percent ceramic content and influenced by a certain degree of agglomeration revealed in the ceramic phase as well as by use of fabrication additives. When increasing percent ceramic amount, the composite materials become lighter, harder, stiffer and slightly stronger, while remaining conductive, although their electrical resistivity increases. Due to differences in matrix composition, Ni3Fe–Al2O3 composites prevail over the (3Ni + Fe)–Al2O3 ones in hardness, and slightly in stiffness and strength, at each percent ceramic content.  相似文献   

16.
《Ceramics International》2017,43(6):5102-5107
This work aimed to improve the acid resistance of an alumina ceramic. Acid corrosion of alumina ceramic composed of Al2O3-CaCO3-SiO2-MgO-Y2O3 (ACSMY) was investigated in a hydrochloric-hydrofluoric acid solution at 65 °C for 30 min. The effect of Y2O3 content on sintering temperature, density, and acid solubility were discussed. The composition and microstructure of this material were analyzed. The acid solubilities of minor crystal phases (Y3Al5O12, CaAl12O19, Ca2Al2SiO7, and CaAl2Si2O8) and the effect of them on acid resistance of this alumina ceramic were studied. The results showed that Y2O3 additive can enhance density and change the type of phases. Phases with good acid resistance and dense structure lead to a crust formed on the surface of ceramic during acid corrosion. The crust can effectively protect the interior structure of the sample from acid solution, and then improve the acid resistance of the material.  相似文献   

17.
《Ceramics International》2015,41(7):8981-8987
Al2O3- and TiO2-based ceramic membranes prepared using polymeric synthesis route were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and gas permeability tests. The influence of the final calcination temperature and the systematic investigation of the properties of the membranes are provided. The calcination temperature affected morphological, structural and chemical properties, as well as the gas permeability of the ceramic membranes. XRD analysis revealed rhombohedral and tetragonal structures of Al2O3 and TiO2-based ceramic, respectively, prepared at calcination temperatures of 1100 and 1200 °C. The TiO2-based ceramic matrix calcined at temperatures of 1100 and 1200 °C exhibited a well-defined crystalline microstructure with the grains increasing in size as a function of temperature. FTIR analysis revealed that phosphorus additives in orthoclase clay tend to form phosphonate groups during the calcination process. The decomposition of organic source was not fulfilled as tested at calcination temperatures of 1000, 1100 and 1200 °C.  相似文献   

18.
《Ceramics International》2017,43(2):1781-1787
Excellent high temperature mechanical properties of melt-grown Al2O3-based eutectics have previously been demonstrated in samples prepared by directional solidification methods. In this study, the deformation behaviour of melt-grown Al2O3/YAG/ZrO2 eutectic bulk prepared by a non-directional solidification method was investigated by means of compressive tests in a temperature range of 1200–1700 °C. The non-directionally solidified eutectic bulk ceramic has a colony structure and is polycrystalline. It begins to show ductility and has a compressive strength of 320 MPa at 1500 °C, which is much higher than that of the sintered ceramic with the same composition. However, its plastic deformability is insufficient, even at 1700 °C (just below the melting point of 1715 °C), and cracking occurs during compressive deformation.  相似文献   

19.
Ca0.9La0.067TiO3 (abbreviated as CLT) ceramics doped with different amount of Al2O3 were prepared via the solid state reaction method. The anti-reduction mechanism of Ti4+ in CLT ceramics was carefully investigated. X-ray diffraction (XRD) was used to analyze the phase composition and lattice structure. Meanwhile, the Rietveld method was taken to calculate the lattice parameters. X-ray photoelectron spectroscopy (XPS) was employed to study the valence variation of Ti ions in CLT ceramics without and with Al2O3. The results showed that Al3+ substituted for Ti4+ to form solid solution and the solid solubility limit of Al3+ is near 1.11 mol%. Furthermore, the reduction of Ti4+ in CLT ceramics was restrained by acceptor doping process and the Q × f values of CLT ceramics were improved significantly. The CLT ceramic doped with 1.11 mol% Al2O3 exhibited good microwave dielectric properties: εr = 141, Q × f = 6848 GHz, τf = 576 ppm/°C.  相似文献   

20.
Bulk glasses containing HfO2 nano-crystallites of 20–50 nm were prepared by hot-pressing of HfO2–Al2O3–Y2O3 glass microspheres at 915 °C for 10 min. By annealing at temperatures below 1200 °C, the bulk glasses were converted into transparent glass-ceramics with HfO2 nano-crystallites of 100–200 nm, which showed the maximum transmittance of ~70% in the infrared region. An increase of annealing temperature (>1300 °C) resulted in opaque YAG/HfO2/Al2O3 eutectic ceramics. The eutectic ceramics contained fine Al2O3 crystallites and showed a high hardness of 19.8 GPa. The fracture toughness of the eutectic ceramics increased with increasing annealing temperature, and reached the maximum of 4.0 MPa m1/2.  相似文献   

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