Papers by Keyword: Silicon Nitride Ceramics

Abstract: Compared with traditional ceramics, Si₃N₄ ceramics have the characteristics of high theoretical thermal conductivity, high thermal shock resistance, high oxidation resistance, high strength, and strong current carrying capacity. It is a potential high-speed circuit and high-power device for heat dissipation and heat dissipation. Sealing material. For applications in 5these fields, β-Si₃N₄ with a relatively stable structure and high thermal conductivity is an ideal material. However, β-Si₃N₄ powder is difficult to sinter as a raw material. Therefore, the prepared Si₃N₄ generally has a low density, and there are various defects in the crystal. The existence of these defects will cause interference and scattering of heat in the transfer process. Limits the application of β-Si₃N₄ ceramics. Studies have shown that the introduction of different additives can form a liquid phase at high temperatures, which can effectively reduce the firing temperature of the sample and increase the density. At the same time, it can also remove lattice oxygen, weaken the intercrystalline phase, and promote the α→β phase transition. Thereby improving the thermal conductivity and sintering performance of Si3N4 ceramics. Therefore, this article reviews the types of additives and their effects on the properties of Si₃N₄ ceramics and their mechanism. Trying to find an additive system for the preparation of high thermal conductivity Si₃N₄ ceramics with excellent comprehensive performance, hoping to provide help for the work and researchers engaged in the research on the thermal conductivity of Si₃N₄ ceramics.

Abstract: A new processing technology is used in micromachining silicon nitride ceramics for improving the processing efficiency. Laser-assisted waterjet machining technology with near damage-free plays an important role in reducing the heat-affected zone (HAZ). In order to understand the effects of process parameters, such as pulse energy, waterjet offset distance and water pressure, on microgrooving of silicon nitride ceramics and the machining performance, a full-factorial experiment with the comparison experiment has been carried out in this study for analyzing and discussing the groove geometry, the surface quality and HAZ width. It can be concluded that the laser-assisted waterjet processing technology can expel more material removal with near damage-free.

Abstract: In order to investigate the mechanism of surface cracks in silicon nitride ceramic (HIP-Si3N4) from the viewpoint of shear stress, the authors focused on torsion fatigue testing and observed the crack growth behavior under conditions where the stress ratio was R = - 1. Furthermore the residual stresses around the cracks were measured. Based on these results, mode II growth of surface cracks is discussed and it was concluded that under stress ratio R = -1, surface cracks grow slowly in mode II, for ΔKⅡ less than 3.6MPam1/2.

Abstract: Thermophysical and tribological measurements have been performed on carbon nanotube added silicon nitride composites. Higher thermal conductivity values were observed in the case of the sample with CNT than for the reference sample. As was observed from tribological measurements, nanocomposite Si3N4 without carbon nanotubes shows a higher friction coefficient than carbon nanotube - Si3N4. The results of wear study indicate that the Si3N4 ball (used as static partner) was more damaged with MWCNTs addition nanocomposite than with pure Si3N4 ceramic. A pronounced difference was observed in the wear rate: there was a much higher wear for carbon nanotube - Si3N4 than for Si3N4 without MWCNTs.

Abstract: Silicon nitride ceramics materials have excellent properties such as small density, high rigidity, high Young's modulus, high wearability, good thermal stability and chemical stability, which make it become one of the most appropriate materials for rollers of high precision bearing. Chemical Mechanical Polishing (CMP) technology is employed to have an ultra-precision machining process for silicon nitride ceramics materials workpiece and the effects of workpiece surface roughness in different abrasive are discussed in this research. The XRD and SEM technology are used to take phase analysis and surface profile detection for the finishing workpiece polished with CeO2 abrasive. The chemical reaction mechanism and the material remove mechanism of silicon nitride ceramics materials in CMP process with CeO2 abrasive are both analysed and discussed in this paper. The research result shows that an extremely smooth surface of silicon nitride ceramics materials workpiece with roughness 5nm Ra is obtained after CMP process with polyurethane polishing pad and CeO2 abrasive.

Abstract: Silicon nitride samples were pressureless sintered with up to 5 w/o MgO to give densities in the range 98-99% of theoretical. After pressureless sintering, selected samples were placed in a vacuum heat treatment furnace surrounded by a carbon bed in a carbon crucible at a pressure of less than 4x10-4 mbar, and vacuum heat treated at different temperatures and times to remove grainboundary glass. The results showed that this was substantially achieved at 1575oC for 3h and that increasing the time to 5 hours gave still further improvement. SEM images, EDX analysis and oxidation tests provided additional evidence for the removal of Mg from the samples.

Abstract: Si3N4 and 40CrMo steel was joined using Ag-Cu-Ti-Pd brazing filler. Microstructure of the joint and bonding interface was studied by SEM and EDS, and the phase structure was analyzed by XRD. The results indicate that reaction layers at ceramic/ filler alloy and filler alloy/steel interfaces are formed. There is a reaction layer containing TiN and Ti5Si3 between ceramic and filler alloy, while the reaction layer between filler alloy and steel is composed of Fe-Ti compound. The middle part of the joint is an eutectic structure composed of Ag-riched and Cu-riched solid solutions. With the increase of the brazing temperature, the thickness of the joint seem decrease, the thickness of the reaction layer between Si3N4 and filler alloy increases and then decreases, and the thickness of the reaction layer between filler alloy and steel increases.

Abstract: Silicon nitride ceramics are finding uses in numerous engineering applications because of their tendency to form whisker-like microstructures that can overcome the inherent brittle nature of ceramics. Studies now establish the underlying microscopic and atomic-scale principles for engineering a tough, strong ceramic. The theoretical predictions are confirmed by macroscopic observations and atomic level characterization of preferential segregation at the interfaces between the grains and the continuous nanometer thick amorphous intergranular film (IGF). Two interrelated factors must be controlled for this to occur including the generation of the elongated reinforcing grains during sintering and debonding of the interfaces between the reinforcing grains and the matrix. The reinforcing grains can be controlled by (1) seeding with beta particles and (2) the chemistry of the additives, which also can influence the interfacial debonding conditions. In addition to modifying the morphology of the reinforcing grains, it now appears that the combination of preferential segregation and strong bonding of the additives (e.g., the rare earths, RE) to the prism planes can also result in sufficiently weakens the bond of the interface with the IGF to promote debonding. Thus atomic-scale engineering may allow us to gain further enhancements in fracture properties. This new knowledge will enable true atomic-level engineering to be joined with microscale tailoring to develop the advanced ceramics that will be required for more efficient engines, new electronic device architectures and composites.