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《Journal of the European Ceramic Society》2020,40(14):4746-4752
Fractography is an important tool to understand and identify the cause of the failure in materials. This understanding can be used to make changes in raw materials selection and processing to increase the strength of brittle materials. This study reports the fracture behavior of hot-pressed silicon nitride based ceramics, with focus on dominant flaw identification with respect to material and process parameters. Silicon nitride is an important material for structural applications which require high strength and wear resistance, such as bearings, nozzles, and cutting tools. Silicon nitride with a target base composition of Si6-zAlzOzN8-z (z = 0.5), along with varying boron dopant levels, was explored in this work. Detailed fractographic analyses revealed that the majority of fracture origins were internal flaws due to the foreign impurities introduced at various stages of processing. All materials were found to have reasonably high strength (800−1100 MPa). Strength was inversely proportional to the square root of the flaw size, however no correlation was found between measured flexural strength and fracture origin types. Mirror constants calculated from fracture mirror measurements ranged between 5.8 and 9.8 MPa.m1/2. 相似文献
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Silicon carbide refractories with binders of silicon nitride and silicon oxynitride are compared with dense aluminum silicate refractories. It is shown that silicon carbide refractories possess high stability in aluminum melts and vapors of aluminum chloride, whereas aluminosilicate refractories are severely damaged under these conditions. Silicon carbide refractories with a binder of silicon nitride possess the highest resistance to the effect of the tested aggressive factors and are recommended for operation in aluminum melts and gaseous aluminum chloride media.Translated from Ogneupory, No. 12, pp. 2–5, December, 1995. 相似文献
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Irina Tsarenko Sang Park Honghua Du Woo Y. Lee 《Journal of the American Ceramic Society》2003,86(9):1622-1624
A 25 nm thick α-alumina layer was deposited on a turbine-grade silicon nitride by sol-gel dip coating and subsequent heat treatment in air at 1200°C. This layer had a nanometer grain structure. Silicon nitride protected by this thin layer showed a significant improvement in oxidation resistance over its uncoated counterpart after 200 cyclic exposures in air at 1250°C. The oxide layer grown on the coated silicon nitride also exhibited superior surface morphology, compared with the uncoated silicon nitride. 相似文献
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《Ceramics International》2020,46(1):795-802
Silicon nitride ceramics are widely used in various industrial fields because of their excellent characteristics: high hardness, high elastic modulus, abrasion resistance, and high heat resistance. Diamond wheel grinding is the predominant and most productive method to machine silicon nitride ceramics. However, a lot of heat is generated due to high friction between a diamond grinding wheel and extremely rigid silicon nitride during grinding. This causes surface/subsurface damage, wheel wear, etc., which impairs the surface quality of silicon nitride. This impairment can restrict the use of silicon nitride ceramic components. To improve the surface quality and service life of grinding wheels, a laser macro-micro combination structured grinding (LMMCSG) method was presented. The results indicated that the grinding force ratio and surface roughness when using LMMCSG were respectively 31% and 40% lower than the grinding force ratio and surface roughness when using conventional grinding. Moreover, the LMMCSG method effectively reduced the wheel wear and workpiece subsurface damage. 相似文献
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A corundum suspension at pH = 7 with a 58% volume concentration of the solid phase and a molding porosity of 20% is prepared. The properties of fused quartz + fused corundum mixed suspensions are studied. Based on a mixed binder of composition 50% SiO2 + 50% Al2O3 and a fused quartz filler, a castable is prepared which, heat treated at 1150°C, exhibited the following properties: open porosity — 13%, compressive — 80 MPa, temperature for strain onset under loading — 1250°C, thermal stability — 10 heat-cool cycles (1000°C – water). The new castable exhibits a higher slag resistance against the conventional quartz-based castable. 相似文献
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Silicon carbide refractory materials and specimens of silicon nitride and silicon oxynitride are tested under high-temperature attack from reducing (H2 and CO) and oxidizing gases (O2, air) and from molten slag, alkalis, and iron. It is shown that nitride-based refractory materials are prone to change their properties, structure, and resistance when exposed to molten slag, iron, and alkalis. Silicon oxynitride and silicon nitride resist attack from carbon monoxide and alkali and provide protection to silicon carbide used as the refractory lining for blast furnaces. 相似文献
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研究了三种不同骨料对Al2O3-尖晶石钢包浇注料性能的影响。结果表明:用电冶矾土刚玉骨科制得的浇注料具有较好的流动性、高温烧结性和抗渣性,但热震稳定性比电熔白刚玉有所降低。这主要与电冶矾土刚玉的组成和显微结构有关。 相似文献
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The influence of carbon nanotubes (CNTs) addition on basic mechanical, thermal and electrical properties of the multiwall carbon nanotube (MWCNT) reinforced silicon nitride composites has been investigated. Silicon nitride based composites with different amounts (1 or 3 wt%) of carbon nanotubes have been prepared by hot isostatic pressing. The fracture toughness was measured by indentation fracture and indentation strength methods and the thermal shock resistance by indentation method. The hardness values decreased from 16.2 to 10.1 GPa and the fracture toughness slightly decreased by CNTs addition from 6.3 to 5.9 MPa m1/2. The addition of 1 wt% CNTs enhanced the thermal shock resistance of the composite, however by the increased CNTs addition to 3 wt% the thermal shock resistance decreased. The electrical conductivity was significantly improved by CNTs addition (2 S/m in 3% Si3N4/CNT nanocomposite). 相似文献
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Silicon - The aim of present study is to investigate the physicochemical and thermophysical behaviour of submerged arc welding slags designed by CaO-SiO2-CaF2 and CaO-SiO2-Al2O3 system. Slag was... 相似文献
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本文综述了沥青、炭黑、焦炭和石墨等常规碳源,表面改性碳以及新型碳源对Al2O3-SiC-C质铁沟浇注料性能影响的研究概况。沥青在Al2O3-SiC-C质浇注料中发挥着重要作用,其加热软化后渗透或挥发、凝结到浇注料的缝隙或气孔中,可以增强颗粒之间的结合,改善高温下液相分布,避免过烧结,显著提高浇注料的抗渣性能。炭黑粒度细小,可充分填充空隙,降低烧后试样的气孔平均孔径,改善高温下抗侵蚀性。炭黑、焦炭和石墨等常规碳源适合作为附加碳源和沥青配合使用,达到互补的效果。表面改性碳中造粒石墨具有较好的应用效果,可大幅提高Al2O3-SiC-C质铁沟浇注料中鳞片石墨的引入量,显著提高抗渣性能。新型碳源中含碳树脂粉Carbores P配合沥青添加到Al2O3-SiC-C质铁沟浇注料中可有效提高铁沟服役寿命。 相似文献
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为制备保温性能及机械性能均较优异的高温窑炉用隔热耐火材料,以多孔球形莫来石、矾土细粉、α-Al2O3微粉、硅微粉和Secar71水泥为主要原料,制备了多孔球形莫来石基浇注料,研究了矾土细粉掺量对多孔球形莫来石基浇注料机械性能、导热系数、抗侵蚀性能及热震稳定性的影响。结果表明,改变矾土细粉的掺量,可使多孔球形莫来石基浇注料在保持较高机械性能的基础上提高保温性、热震稳定性和抗侵蚀性能。随着矾土细粉掺量的增加,多孔球形莫来石基浇注料的机械性能变化不大,但导热系数小幅降低,抗侵蚀性能出现较大差异,热震稳定性先提高后降低。当矾土细粉掺量为28%(质量分数)时,多孔球形莫来石基浇注料的机械性能、热震稳定性及抗侵蚀性能良好,在1 000 ℃时导热系数为0.905 W·m-1·K-1。多孔球形莫来石基浇注料的导热系数低于中间包和钢包永久层用高铝浇注料,可替代中间包、钢包永久层用高铝浇注料以减少热损失。 相似文献