Flash Sintering Method Research Articles

Fabrication and electrical characteristics of flash-sintered SiO2-doped ZnO-Bi2O3-MnO2 varistors

The dense ZnO-Bi2O3-MnO2-xSiO2 (ZBMS) varistors for x = 0, 1, 2, 3 wt% were fabricated by flash sintering method under the low temperature of 850 °C within 2 min. The sample temperature was estimated by a black body radiation model in the flash sintering process. The crystalline phase assemblage, density, microstructure, and electrical characteristics of the flash-sintered ZBMS varistors with different SiO2-doped content were investigated. According to the XRD analysis, many secondary phases were detected due to the SiO2 doping. Meanwhile, the average grain size decrease with increasing SiO2-doped content. The improved nonlinear characteristics were obtained in SiO2-doped samples, which can be attributed to the ion migration and oxygen absorption induced by the doped SiO2. The flash-sintered ZBMS varistor ceramics for x = 2 wt% exhibited excellent comprehensive electrical properties, with the nonlinear coefficient of 24.5, the threshold voltage and leakage current of 385 V·mm−1 and 11.8 µA, respectively.

Fabrication of titanium carbide-reinforced iron matrix composites using electropulsing-assisted flash sintering

As a potential substitute for tungsten carbide-cobalt, titanium carbide-reinforced iron matrix composites with different titanium carbide content were fabricated using flash sintering. The as received mixed titanium carbide and steel powders were directly loaded into a mold and sintered for 10 s. Few voids were visible in the sintered samples using optical and scanning electron microscopes, which suggested that the samples were completely dense. As the titanium carbide content increased, the hardness of the samples linearly increased from 700 HV to 1350 HV. However, the addition of titanium carbide particles reduced the compressive strength of the samples from 3.5 GPa (5 wt% titanium carbide) to 1.5 GPa (50 wt% titanium carbide). The increasing porosity at the phase boundary and decreased free path of the binder network caused the strength of the sintered samples to decrease. The excellent bond strength at the interface between titanium carbide and the high-speed steel matrix is an indication for the excellent application potential of this cemented carbide. In addition, the electropulsing-assisted flash sintering method described in this paper should be feasible for all other conductive composites and could provide a pathway for the ultrafast fabrication of ceramic-reinforced metal composites.

Microstructure and dielectric property of flash sintered SiO2-coated BaTiO3 ceramics

Flash sintering method was adopted to sinter SiO2-coated BaTiO3 ceramics to lower sintering temperature and shorten sintering time. The microstructure and dielectric property of BaTiO3 with different amount of SiO2 coating were studied. Samples can be flash sintered at furnace temperatures lower than conventional sintering temperature. Though the onset flash sintering temperature increased obviously with increasing SiO2 content, the estimated sample temperatures were found close to each other. Samples with improved density was achieved with higher SiO2 content, but their dielectric constant decreased. Flash sintered samples with 1.5 wt% SiO2 addition possess a fair dielectric constant with improved density.

Preparation of a high spectral emissivity TaSi2-based hybrid coating on SiOC-modified carbon-bonded carbon fiber composite by a flash sintering method

The most recent and innovative metal disilicide-based hybrid coatings are used for protecting carbon fiber-based composites in aerospace application. Here, we investigate a high emissivity coating on SiOC-modified carbon-bonded carbon fiber composites (SiOC/CBCF) for thermal protection material. Both tantalum silicide (TaSi2) and molybdenum silicide (MoSi2)-based coatings are prepared on SiOC/CBCF composites using flash sintering method, and the emissivity value of MoSi2-based coating is higher than that of TaSi2-based coating. Significantly, improvement the density of the coating has a positive role on emissivity resulting in MoSi2-based coating increases about 7.2% at 400 °C and 11.5% at 1000 °C, respectively; TaSi2-based coating increases about 15.4% at 400 °C and 2.6% at 1000 °C. After exposure to 1500 °C for 60 min in air, the emissivity values of the coated-samples are also investigated.

Microwave flash sintering of metal powders: From experimental evidence to multiphysics simulation

Flash sintering phenomena are predominantly associated with ceramics due to thermal runaway of their electric conductivity noticeably represented in materials such as zirconia or silicon carbide. Because of their high electric conductivity, flash sintering of metals is nearly inexistent. In this work, an original metal powder flash sintering method based on a microwave approach is presented. Within the developed approach, an unusually fast (60 s) thermal and sintering runaway of Ti-6Al-4V powder is experimentally revealed under microwave illumination. This phenomenon is simulated based on an electromagnetic-thermal-mechanical (EMTM) model. The developed multiphysics model reveals that the metal powder specimen's runaway does not result from its intrinsic material properties, but results from the resonance phenomenon thermally activated by the surrounding tooling material. The EMTM simulation predicts with a very good accuracy the microwave repartition and the resulting densification and powder specimen's shape distortions observed experimentally. The comparison of the microwave and conventional sintering kinetics indicates an important acceleration of the sintering behavior under microwave heating. The developed sintering approach has a potential of the implementation for time-effective mass production of small metal parts.

Electric field-assisted flash sintering of CaCu3Ti4O12: Microstructure characteristics and dielectric properties

The electric field-assisted flash sintering method recently introduced in the literature was here considered for producing high-quality CaCu3Ti4O12 electroceramics, from a powder originally synthesized by a Pechini-derived method and calcined at 800 °C for 2 h. The study included analyzing the dynamics of material shrinkage and densification. With increasing the electric field (E), three distinct regimes were observed: a conventional-like sintering behavior for E < 15 V/cm, followed by a region of accelerated (fast-dominated) sintering for 15 ≲ E < 30 V/cm, and then the flash-dominated regime, for E ≳ 30 V/cm, where sintering is not only accelerated but occurs suddenly. In consequence, sintering of the material under field input takes place at furnace temperatures sensibly lower, reaching a value as low as 750 °C for E = 60 V/cm versus 1050 °C in conventional processing. The probable physical mechanism behind each regime, including the role of the rise in sample temperature induced by the applied field (Joule heating), is also discussed. Finally, a correlation was found between the microstructure characteristics achieved during sintering and the dielectric response measured.

인공경량골재 내부에 발생하는 방사형 균열의 억제 방법에 관한 연구

본 연구에서는 잔사회와 준설토로 제조된 구형의 인공경량골재 내부에 생성되는 방사형 균열의 원인 및 그 억제 방법에 대하여 연구하였다. 인공경량골재는 잔사회와 준설토를 각각 7 : 3의 무게 비로 혼합하고 직경이 5~20 mm인 구 형태로 성형한 후 <TEX>$1200^{\circ}C$</TEX>에서 10분간 직화소성법으로 제조하였다. 골재 내부의 균열은 골재 지름이 작을수록 발생이 억제되었다. 또한 <TEX>$SiO_2$</TEX> 분말을 첨가한 경우, 분말의 크기가 클수록 또는 첨가량이 증가할수록 방사형 균열 발생이 억제되었다. 균열이 억제된 인공경량골재의 비중은 1.3~1.6이고, 흡수율은 5~20 %의 범위를 나타내었다. 따라서 본 논문에서 제조된 인공경량골재는 건설 및 환경소재 등 여러 분야에 적용 가능할 것으로 보이며, 더불어 잔사회 및 준설토의 재활용율을 높이는데 크게 기여할 것으로 기대된다. In this study, prevention methods of radial cracks generated inside of artificial lightweight aggregate made of reject ash and dredged soil were investigated. The reject ash and dredged soil had mixed with weight ratio of 7 : 3 and formed to spheric shape of 5~20 mm diameter, then, the aggregates were manufactured using flash sintering method at <TEX>$1200^{\circ}C$</TEX> for 10 min. The formation of radial cracks in the aggregates were suppressed as the size of specimen decreased. Also, the addition of silica to aggregates had prevented generation of the radial cracks. As the size and the amount of silica powder added increased, the development of radial cracks was constrained. Therefore the artificial lightweight aggregate manufactured in this study expected to be applicable to many fields such as construction and environmental usages. Also it is expected to contribute greatly to increase the recycling rate of reject ash and dredged soil.

The role of non-stoichiometric defects in radiation damage evolution of SrTiO3

The response of polycrystalline SrTiO3, fabricated by the flash sintering method, to ion beam irradiation was investigated by means of transmission electron microscopy (TEM) and atomic scale modeling. The samples were implanted with 250 keV Ne ions at fluences between 1.11 × 1016 and 2.25 × 1016 ions per cm2 at room temperature and then characterized using scanning transmission electron microscopy and high voltage TEM. We observed that this material has a large number of Ruddlesden–Popper (RP) faults, related to the non-stoichiometry of the material, in a random and sometimes complicated arrangement. These faults have a significant impact on the radiation damage evolution of the material. In particular, the faults amorphize more quickly than the surrounding SrTiO3 matrix. We examined the interaction of point defects with the RP faults using atomistic modeling and determined that both the thermodynamic and kinetic properties of defects are significantly influenced by the presence of the faults, providing insight into the experimental observations. We conclude that planar defects such as RP faults can have a significant impact on the radiation damage evolution of SrTiO3 and might be one avenue for controlling radiation tolerance in complex materials.

On the Sintering Process of the Cermets of TiC System

An apparatus for measuring the shrinkage of cermet in hydrogen atmosphere was designed, and was used successfully for following up the process of sintering. Also the close examinations under the optical and electron microscopes have added some useful informations. The results may be summarized in the following outline.1) The velocities of shrinkage under different conditions, and the mode of approaching to an equilibrium value at a certain temperature as well as the subsequent shrinkage by the repeated heating at higher temperatures have revealed that the sintering was governed mainly by temperature but not by holding time. It may, therefore, be concluded that the heating schedule of very short holding time at higher temperature is by far better than the usual one.2) Sintering started by the thermal diffusion of the materials along the contact surface between the particles which were pressed strongly by the forming process. The increase of the path of diffusion brought about of the decrease of the distance between the particles, and the shrinkage of the mass was observed. When the temperature was too high the perspiration of metal bonding was observed.3) Sintering by an instantaneous heating, i.e. so called flash sintering method showed no sign of grain growth.4) Observations under electron microscope have revealed that the rupture of TiC cermets occured in two ways, viz. trans-crystal and inter-crystal, according to tha heating temperature.