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1.
《Ceramics International》2017,43(18):16340-16347
Zirconia (ZrO2) ceramic bars with three different printing sizes were fabricated by a stereolithographic (SLA) 3D-printing process and subsequent sintering. An anisotropic character of the ceramics surface quality was observed. The surface roughness of the horizontal surface was below 0.41 µm, whereas it reached 1.07 µm along the fabrication direction on the vertical surface. The warpage and flatness were utilized to measure the dimensional accuracy of the 3D printed ZrO2. Furthermore, it was evaluated that the warpage and flatness were below 40 µm and 27 µm, respectively, even if the printed size of ceramic bar reached 3 mm × 4 mm × 80 mm. In addition, the flexural strength, the fracture toughness, the hardness and the density of ZrO2 ceramics can reach to 1154 ± 182 MPa, 6.37 ± 0.25 MPa m1/2, 13.90 ± 0.62 GPa and up to 99.3%, respectively. Moreover, the effects of scanning paths and printing size on properties of the sintered ZrO2 samples were analyzed. The anisotropic character of surface quality was related to the various scanning paths. The warpage and flatness of 3D printed ZrO2 bars were apparently affected by the various printed sizes. Also, the effects of special microstructure on the mechanical properties of sintered ZrO2 samples were investigated. 相似文献
2.
《Journal of the European Ceramic Society》2014,34(10):2203-2209
Ultra high temperature ceramics (UHTCs) based composite ZrB2/20 vol.% Cu was prepared by spark plasma sintering (SPS) at 1650 C° for 3 min. The ablation behavior of composite irradiated for 2–20 s by 20 MW/m2 high-intensity continuous laser was investigated. The phase and microstructure evolution of ZrB2/20 vol.% Cu during ablation was demonstrated by XRD and SEM, respectively. The results reveal that no macroscopic damage but only one ablated layer with 40 μm in thickness is observed even after being ablated for 20 s. It implies that ZrB2/20 vol.% Cu composite exhibits good ablation resistance against high-intensity continuous laser. The continuous Cu in composite evaporates preferentially, which impacts on the following ablation behavior. The generated ZrO2 at the spot center shows different forms such as closely packed nano-ZrO2, micron ZrO2 or melting ZrO2 for different ablation time. The melting ZrO2 is helpful to promote the ablation resistance of ZrB2/20 vol.% Cu. 相似文献
3.
《Journal of the European Ceramic Society》2017,37(5):2303-2308
In this communication, the cold sintering process was applied to benefit the green body compaction of 8 mol%Y2O3-stablized ZrO2 ceramics (8Y-YSZ). Compared to conventionally processed ceramics, an enhanced densification behavior was demonstrated in cold sintering related ones following a second step conventional sintering process. Dense ceramics up to ∼96% of theoretical density were achieved after sintering at 1200 °C. The resulted ceramics demonstrated a fine microstructure with a grain size ∼200 nm. A mechanical performance with a Vickers hardness of 13.6 GPa and a fracture toughness of 2.85 MPa m1/2 was also reported. 相似文献
4.
《Journal of the European Ceramic Society》2017,37(1):223-227
Cerium-doped yttrium aluminum garnet (YAG:Ce) phosphor ceramics were fabricated by CO2 laser sintering under various powers. X-ray diffraction results indicated that all samples crystallized as a YAG phase without any impurity phase in the power range of 15–40 W. The reaction profile caused by laser ablation increased from 0.28 mm (15 W) to 2.68 mm (40 W), and it appeared deeper in the scanning sequence because of the low rigidity of YAG melts compared with solid precursors. Photoluminescence (PL) measurements revealed that the YAG:Ce sample by 15 W laser sintering upon blue light excitation presented more intense yellow emission (enhancement of 54%) as compared with YAG:Ce by solid-state reaction (SSR, 1500 °C). The laser beams were believed to distribute activators (Ce) more homogeneously compared with SSR. Additionally, a rougher surface of YAG:Ce phosphor ceramics with periodic holes caused by laser ablation resulted in more excitation and emissivity of PL. 相似文献
5.
《Ceramics International》2017,43(16):13127-13132
In this study, we report highly transparent Er:Y2O3 ceramics (0–10 at% Er) fabricated by a vacuum sintering method using compound sintering additives of ZrO2 and La2O3. The transmittance, microstructure, thermal conductivity and mechanical properties of the Er:Y2O3 ceramics were evaluated. The in-line transmittance of all of the Er:Y2O3 ceramics (1.2 mm thick) exceeds 83% at 1100 nm and 81% at 600 nm. With an increase in the Er doping concentration from 0 to 10 at%, the average grain size, microhardness and fracture toughness remain nearly unchanged, while the thermal conductivity decreases slightly from 5.55 to 4.89 W/m K. A nearly homogeneous doping level of the laser activator Er up to 10 at% in macro-and nanoscale was measured along the radial direction from the center to the edge of a disk specimen, which is the prominent advantage of polycrystalline over single-crystal materials. Based on the finding of excellent optical and mechanical properties, the compound sintering additives of ZrO2 and La2O3 are demonstrated to be effective for the fabrication of transparent Y2O3 ceramics. These results may provide a guideline for the application of transparent Er:Y2O3 laser ceramics. 相似文献
6.
《Journal of the European Ceramic Society》2014,34(1):45-53
Phase transformations in ZrO2 + xSc2O3 solid solutions (6.5 < x < 11 mol%) at sintering of ceramics obtained from nanopowders produced by laser evaporation of the ceramic targets have been studied. The Sc2O3 concentration increasing from 6.5 to 11 mol% is accompanied by the sintering temperature decreasing and the average grain size growth from 130 nm to 760 nm. At concentration of about 7 mol% Sc2O3 an abrupt increase of the average grain size and electric conductivity is observed. The sinterability of the ZrO2 − хSc2O3 ceramics is affected by the prehistory of nanopowders preparation. The characteristics of ceramics obtained from nanopowders evaporated from the targets based on (ZrO2 + xmol% Sc2O3) mixture and on the (ZrO2 − 11mol% Sc2O3) solid solution significantly differ, namely, in the latter the sintering temperature is markedly lower and the shrinkage rate is higher. Besides, its average grain size is substantially lower and the conductivity is higher. 相似文献
7.
《Ceramics International》2016,42(15):17074-17080
The effects of Fe and SiC additions on the densification, microstructure, and ablation properties of ZrB2-based ceramics were investigated in this study. The sample powders were conventionally mixed by cemented carbide ball then sintered by spark plasma sintering. The ablation rates and behavior of the ceramics were investigated under an oxyacetylene torch environment at about 3000 °C. A sample with high relative density (96.3%), high flexural strength (415.6 MPa), and low linear ablation rate (−0.4 µm/s) was obtained via SPS at 1600 °C. Adding 4 vol% Fe was more beneficial to the density of ZrB2 sintered at 1600 °C as compared to ZrB2 sintered at 1800 °C. The ablation behavior and rates were similar among samples sintered at 1600 °C and 1800 °C. 相似文献
8.
《Ceramics International》2017,43(4):3647-3653
This study investigated the effect of sintering temperature on the microstructure and mechanical properties of dental zirconia-toughened alumina (ZTA) machinable ceramics. Six groups of gelcast ZTA ceramic samples sintered at temperatures between 1100 °C and 1450 °C were prepared. The microstructure was investigated by mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques. The mechanical properties were characterized by flexural strength, fracture toughness, Vickers hardness, and machinability. Overall, with increasing temperature, the relative density, flexural strength, fracture toughness, and Vickers hardness values increased and more tetragonal ZrO2 transformed into monoclinic ZrO2; on the other hand, the porosity and pore size decreased. Significantly lower brittleness indexes were observed in groups sintered below 1300 °C, and the lowest values were observed at 1200 °C. The highest flexural strength and fracture toughness of ceramics reached 348.27 MPa and 5.23 MPa m1/2 when sintered at 1450 °C, respectively. By considering the various properties of gelcast ZTA that varied with the sintering temperature, the optimal temperature for excellent machinability was determined to be approximately 1200–1250 °C, and in this range, a low brittleness index and moderate strength of 0.74–1.19 µm−1/2 and 46.89–120.15 MPa, respectively, were realized. 相似文献
9.
The screen-printing multilayer grain growth (MLGG) technique is successfully applied to alkaline niobate lead-free piezoelectric ceramics. Highly textured (K0.5Na0.5)NbO3 (KNN) ceramics with 〈0 0 1〉 orientation (f = 93%) were fabricated by MLGG technique with plate-like NaNbO3 templates. The influence of sintering temperature on grain orientation and microstructure was studied. The textured KNN ceramics showed very high piezoelectric constant d33 = 133 pC/N, and high electromechanical coupling factor kp = 0.54. These properties were superior to those of conventional randomly oriented ceramics, and reach the level of those of textured KNN ceramic prepared by tape-casting technique. Compared with other grain orientation techniques, screen-printing is a simple, inexpensive and effective method to fabricate grain oriented lead-free piezoelectric ceramics. 相似文献
10.
《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
11.
《Ceramics International》2017,43(11):8525-8530
Commercial Y2O3 powder was used to fabricate Y2O3 ceramics sintered at 1600 °C and 1800 °C with concurrent addition of ZrO2 and La2O3 as sintering aids. One group with different contents of La2O3 (0–10 mol%) with a fixed amount of 1 mol% ZrO2 and another group with various contents of ZrO2 (0–7 mol%) with a fixed amount of 10 mol% La2O3 were compared to investigate the effects of co-doping on the microstructural and optical properties of Y2O3 ceramics. At low sintering temperature of 1600 °C, the sample single doped with 10 mol% La2O3 exhibits much denser microstructure with a few small intragranular pores while the samples with ZrO2 and La2O3 co-doping features a lot of large intergranular pores leading to lower density. When the sintering temperature increases to 1800 °C, samples using composite sintering aids exhibit finer microstructures and better optical properties than those of both ZrO2 and La2O3 single-doped samples. It was proved that the grain growth suppression caused by ZrO2 overwhelms the acceleration by La2O3. Meanwhile, 1 mol% ZrO2 acts as a very important inflection point with regard to the influence of additive concentration on the transmittance, pore structure and grain size. The highest in-line transmittance of Y2O3 ceramic (1.2 mm in thickness) with 3 mol% of ZrO2 and 10 mol% of La2O3 sintered at 1800 °C for 16 h is 81.9% at a wavelength of 1100 nm, with an average grain size of 11.2 µm. 相似文献
12.
《Journal of the European Ceramic Society》2014,34(1):81-89
Thermally induced phase separation (TIPS) was used to produce spherical polypropylene–zirconia composite powder for selective laser sintering (SLS). The influence of the composition of the composite starting powder and the SLS parameters on the density and strength of the composite SLS parts was investigated, allowing realizing SLS parts with a relative density of 36%. Pressure infiltration (PI) and warm isostatic pressing (WIPing) were applied to increase the green density of the ZrO2–PP SLSed parts. Infiltrating the SLS parts with an aqueous 30 vol.% ZrO2 suspension allowed to increase the sintered density from 32 to 54%. WIPing (135 °C and 64 MPa) of the SLS and SLS/infiltrated complex shape green polymer–ceramic composite parts prior to debinding and sintering allowed raising the sintered density of the 3 mol Y2O3 stabilized ZrO2 parts to 92 and 85%, respectively. 相似文献
13.
Hai-Tao Liu Ji Zou De-Wei Ni Ji-Xuan Liu Guo-Jun Zhang 《Journal of the European Ceramic Society》2012,32(12):3469-3476
Oxidation behavior of hot forged textured ZrB2–20 vol% MoSi2 ceramics with platelet ZrB2 grains was investigated at 1500 °C for exposure time from 0.5 to 12 h. Compared to untextured ceramics, the textured ceramics showed obvious anisotropic oxidation behavior and the surface normal to the hot forging pressure demonstrated better oxidation resistance. Such improvement in the oxidation resistance is primarily considered as a higher intrinsic ZrB2 atomic density on the orientated {0 0 l} planes in the textured ceramics. It is expectable that the anisotropic textured ZrB2–MoSi2 ceramics can offer better oxidation resistance when a certain surface with higher oxidation resistance is exposed to air at elevated temperature. 相似文献
14.
《Ceramics International》2016,42(10):11709-11715
Nanocrystalline gamma alumina (γ-Al2O3) powder with a crystallite size of ~10 nm was synthesized by oxidation of high purity aluminium plate in a humid atmosphere followed by annealing in air. Spark plasma sintering (SPS) at different sintering parameters (temperature, dwell time, heating rate, pressure) were studied for this highly porous γ-Al2O3 in correlation with the evolution in microstructure and density of the ceramics. SPS sintering cycles using different heating rates were carried out at 1050–1550 °C with dwell times of 3 min and 20 min under uniaxial pressure of 80 MPa. Alumina sintered at 1550 °C for 20 min reached 99% of the theoretical density and average grain size of 8.5 µm. Significant grain growth was observed in ceramics sintered at temperatures above 1250 °C. 相似文献
15.
A new method was developed for the fabrication of complex-shaped Al2O3 ceramic parts by combining laser machining and gelcasting technique. The unwanted ceramic powders parts were selectively removed by laser machining specified by a computer program, and the gelcast Al2O3 green bodies were machined to a designed shape by a CO2 laser at a wavelength of 10.6 μm. The influences of solid loading, laser output power, scanning speed and nitrogen purge on the machining of green Al2O3 ceramic bodies were studied. The experimental parameters were optimized, the green Al2O3 bodies with solid loading of 40 vol% or below were easier to be machined, while the green bodies with solid loading of 45 vol% or above were hard to be further machined due to the surface sintering. Better machining quality and deeper machining depth could be obtained when the laser power is 30 W. The green Al2O3 bodies with complex shape were obtained by the laser machining. 相似文献
16.
《Ceramics International》2015,41(7):8273-8281
Reactive spark plasma sintering (SPS) of WB2/WB3 ceramics from elements is studied; the sintering pressure dependence of the ratio of WB3 to WB2 in samples produced by SPS is discussed. Regardless of the sintering pressure, the obtained samples are very hard ~20 GPa. WB3 superhard films prepared by pulsed laser deposition (PLD) from selected SPS targets are presented.WB3 coatings were prepared on Si (100) substrates using a nanosecond, Nd:YAG laser operating at a 355 nm wavelength. The phase analysis, crystallography, and orientations have been studied using X-ray diffraction (XRD). A WB2 to WB3 phase transformation from 8.2% WB3 in a sintered target to 93.3% WB3 in a deposited film was observed. Additionally, the surface of a SPS sintered WBx target after the ablation process was examined. XRD studies show that already during the laser ablation there is a significant WB2 to WB3 phase transformation. Vickers hardness of sintered samples was measured in macro- and micro-scale, and PLD films in the nanoscale. 相似文献
17.
《Ceramics International》2017,43(15):12057-12060
Transparent Sm:Y2O3 ceramics were fabricated by spark plasma sintering (SPS). The effects of LiF additive and sintering temperature on the microstructure and optical transmittance of the Sm:Y2O3 ceramics were investigated. The optimal content of LiF additive and sintering temperature was found to be 0.3 wt% and 1500 ℃. The transmittance of Sm:Y2O3 ceramics with a thickness of 1.7 mm reached 75.3% at 609 nm, which is about 94% of the theoretical value. The average grain size of the sample was about 50 µm. 相似文献
18.
《Ceramics International》2017,43(5):3970-3974
ZTA ceramics containing 20 wt% ZrO2 were fabricated at different sintering temperatures (1450, 1500 and 1550 °C) by SPS and HP processes, respectively. The influence of sintering process on the mechanical properties of ZTA ceramics at 298 K and 77 K was investigated. It can be seen that the bending strength and fracture toughness of samples prepared by the two processes both improved at cryogenic temperature. The stress-induced martensitic transformation toughening mechanism was confirmed by the in-situ Raman technique. The tetragonal ZrO2 would be even more easy to transform because of the residual stress generated when temperature decreased from 298 K to 77 K. Therefore, the transformation toughening effect would become stronger, result in the increase of mechanical properties. 相似文献
19.
Yen-Lin Huang Ying-Chieh Lee Du-Cheng Tsai Jam-Da Chiu Fuh-Sheng Shieu 《Journal of the European Ceramic Society》2013,33(13-14):2609-2615
The effects of Mn3O4 addition and reductive atmosphere (N2:H2 = 97:3) annealing on the microstructure and phase stability of yttria stabilized zirconia (YSZ) ceramics during sintering at 1500 °C for 3 h in air and subsequent annealing in a reductive atmosphere were investigated. Mn3O4 added 6 mol% YSZ (6YSZ) and 10 mol% YSZ (10YSZ) ceramics were prepared via the conventional solid-state reaction processes. The X-ray diffraction results showed that a single cubic phase of ZrO2 was obtained in 1 mol% Mn3O4 added 6YSZ ceramic at a sintering temperature of 1500 °C for 3 h. A trace amount of monoclinic ZrO2 phases were observed for 1 mol% Mn3O4 added 6YSZ ceramics after annealing at 1300 °C for 60 cycles in a reductive atmosphere by transmission electron microscopy. Furthermore, a single cubic ZrO2 phase existed stably as Mn3O4 added 10YSZ ceramics was annealed at 1300 °C for 60 cycles in reductive atmosphere. 相似文献
20.
Igor Danilenko Fedor Glazunov Tetyana Konstantinova Galina Volkova Valerij Burkhovetski 《Journal of the European Ceramic Society》2013,33(12):2321-2325
We have studied the effect of NiO on the sintering of yttria-stabilized zirconia at temperatures ranging from 1300 °C to 1500 °C in air and argon environments. It was found that the addition of NiO stabilized the cubic phase of ZrO2 independently from the sintering atmosphere. The monoclinic phase of ZrO2 formed only during sintering within the air environment at temperatures higher than 1450 °C. The transformation of NiO to Ni by reversible decomposition depends on the sintering atmosphere, and this can lead to variations in the nature of inclusions and in changes of the structure and properties of nanocomposite materials in the system ZrO2–NiO(Ni). NiO and Ni inclusions can increase the indentation fracture toughness of zirconia–nickel oxide composite material more than 50%, which can be compared with zirconia ceramics during sintering in a neutral atmosphere alone. 相似文献