Papers by Keyword: Si₃N₄ Ceramic

Abstract: In this Study, a Good Combination between Si₃N₄-Based Seal Coatings and Porous Si₃N₄ Substrate Was Achieved by Room Temperature Spraying and Pressureless Sintering. To Evaluate the Joint Quality, Residual Stress due to Thermal Expansion Mismatch between the Coatings and Porous Layers Were Characterized by Computational Studies Using the Finite Element ANSYS Code. It Was Found that Si₃N₄-Based Seal Coating Allows a Gradual Change in Thermal Expansion Mismatch, Minimizing the Thermal Stresses Arising from Cooling or Heating. Further Theoretical Analysis Indicates that the Thermal Expansion Mismatch between the Two Layers Produced a Large Strengthening Effect for the Fraction of the Porosity below a Critical Level and that Substrates with the High Fraction of Porosity Showed Complete Cracking, as the Cracks Initiating in Adjacent Coatings. And the Volume Fraction of Pores Required to Cause Crack Deflection, in the Porous Layer, Was Predicted. The Effects of Layer Thickness and Porosity Fraction on Residual Stress Were Studied, which Are Used as Predictions towards Better Design of Composite Materials.

Abstract: Si3N4 ceramics have been fabricated through pressureless sintering and hot-pressing sintering with MgSiN2-Y2O3 or only MgSiN2 as sintering additive, respectively. The effects of MgSiN2 and Y2O3 and sintering methods on sintering properties of Si3N4 ceramics were studied. The results indicate that the bend strength of Si3N4 ceramic with 5.6wt.%MgSiN2-15.8wt.%Y2O3 sintered at 1820°C for 4h could achieve 839MPa. The bend strength of Si3N4 ceramic with 4.76wt.%MgSiN2 produced by hot-pressing sintering at 1750°C for 1h under uniaxial pressure of 20MPa is 1149MPa. The thermal conductivity of the Si3N4 ceramic was 92Wm-1K-1 and could remarkably increase to 129Wm-1K-1 by prolonging the sintering time from 1 h to 12 h. The present work demonstrated that MgSiN2 additives and hot-pressing sintering were effective to improve the thermal conductivity of Si3N4 ceramic.

Abstract: A series of experiment were performed to test the cleaning ability of different organic emulsion for Si₃N₄ ceramic grinding. The experiment results showed that the grinding fluid made by short chain organic substance and alkane will induces the jam of grinding wheels. At the same time, polar organic substance with long carbon chain can suppress wheel loading phenomenon. The main reason of the jam by alkane is the nonpolar oil film surface possesses the strong attraction to abrasive dust of Si₃N₄, which will lead to jam in the grinding process. The polar oil film relieves the aggregation of abrasive dust in the grinding area to some extant, which is beneficial to decrease jam. By analyzing the cleaning property by some types of polar organic substances, the paper discusses the relationships of molecular structure characters to their cleaning ability.

Abstract: A series of experiment were performed to test the cleaning ability of different alkane emulsion for Si3N4 ceramic grinding. The experiment results showed that the adsorption film surface of nonpolar alkane have strong attraction to Si3N4 abrasive dust, which will make abrasive dust to gather at the grinding area and finally led to jam. To add alkane grinding fluid with polar organic substances is beneficial to decrease jam. The best additive for anti block is which integrate hydrophobic group and hydrophilic group, both are indispensable.

Abstract: A series of experiment were performed to test the tribological properties of Si3N4 ceramic pair lubricated by emulsions of alkane. The experiment results showed that all alkane are very efficient lubricator for Si3N4 ceramic pair. The straight chain alkanes can perform better than branched paraffin or polycyclic saturated hydrocarbon. When added the liquid paraffin with chlorinated paraffin or Oleic acid, the lubrication property become poor. But added with silicone oil emulsion，the lubrication improve further. Base on the molecular structure of reagents, the causative mechanisms is investigated.

Abstract: MDAM technology is a brand-new and low-cost machining technology. Based on the brief introduction of MDAM system, the generator structure and additional anode access method are in-depth studied. The results show that the cost of consumable parts can be reduced to a minimum of only 10.9% of the original design for optimized generator based on cost reduction, but have the problems of lifespan reduction and frequently replacement. Cost and efficiency are considered comprehensively in the design of final optimized generator, which not only extends the lifespan of consumable pieces about 4 times and improves machining efficiency, but also reduces the cost to only 36.4% of the original design. So it is adopted by the system. On the choice of additional anode access methods, through comprehensive comparison, the method of additional anode attaching with the nozzle directly is ascertained, which is simple and easy realized, and reduces the damage to the surface and sub-surface during the machining of ceramics and other brittle materials. The results lay a solid foundation for further technology promotion.

Abstract: Mo particles have been introduced into Ag-Cu-Ti brazing alloy for the joining of Si3N4 ceramic. Effects of Ti content on microstructure and mechanical properties of the joints were investigated. The results present that a compact reaction layer which is composed of TiN and Ti5Si3 was formed at the Si3N4/solder interface. The central part of the joint was composed of Ag based solid solution, Cu based solid solution, Mo particles and Cu-Ti intermetallics. By increasing Ti content in the composite filler, both the thickness of reaction layer and the amount of Cu-Ti intermetallics in the joint increased, which is beneficial for the joint strength. However, the reaction between Ti and Si3N4 proceeded more excessively. Simultaneously, more Cu-Ti intermetallics were precipitated while elevating Ti content to 6wt.%, leading to deterioration of the bonding strength. The maximum bending strength (429.4MPa) was obtained when Ti content is 4wt.% in the composite filler.

Abstract: Si3N4 ceramic surface was metallized using multi-ionic composite coating technology. The obtained Cu-Ni-Ti composite coating was examined and evaluated by energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), X-ray diffusion (XRD) and sound emissive scratch test (SEST). The composite coating composition, the element distribution, the phase structure of the deposited coating, and the jointing mechanism of steel/ceramics were analyzed. It was found that the obtained alloy coating layer contained elements such as Cu, Ti, Ni and Fe, etc, and no element segregation was observed. XRD result showed that the diffusion coating alloy layer was composed of Cu2Ti4O, Cu, NiTi and CuTi2. Sound emissive scratch test (SEST) results revealed a good adhesion between the diffusion coating alloy layer and ceramic, and no spallation occurred under the maximum load of 100N.

Abstract: Electrically conductive Si3N4 ceramics were fabricated by dispersion of different characteristics of carbon nanotubes (CNTs). When the sintering aid of Y2O3-Al2O3-TiO2-AlN was used for lower temperature densification, it was confirmed that CNTs existed in Si3N4 ceramics from SEM observation and SiC was not identified in XRD analysis, which means that CNTs did not react with Si3N4. Relative density and electrical conductivity of the CNT dispersed Si3N4 ceramics depended on the characteristics of CNTs. Aggregation of CNTs, which is outstanding in much thinner CNTs, should limit densification of Si3N4. CNTs were well-dispersed by beads milling in ethanol. As a result, beads milling process was confirmed to be effective in unraveling and dispersing CNTs. It was shown that better dispersion of CNTs with higher aspect ratio resulted in higher density and electrical conductivity.

Abstract: Slurry pumps are used to transport the liquid fluids with solid particles in the industries. The materials of flow passage in a slurry pump are subjected to severe damage due to abrasive erosion. This paper compares the abrasive erosion for an engineering ceramics i.e. hot pressed Si3N4 ceramics and a high chrome cast iron i.e. Cr26 by laboratory test and industrial operation. The results indicate that the erosion rate of Cr26 is much larger than that of hot pressed Si3N4 ceramics under the same test conditions. That indicates that the engineering ceramics is a promising alternation of the expensive material such as Cr26 in the application of slurry pumps. It is noted that the erosion pattern such as scale ripple has the similar features for both materials, even the hardness of hot pressed Si3N4 ceramics is much higher than Cr26. Further, the scale ripple is suspected to be originated from the relatively weak grain boundary and enhanced by cavitation.