Modification Of Silicon Nitride Ceramic And Precise Molding Of Components

Si₃N₄ and Si₃N₄/ SiC are high temperature structural ceramics widely researched and applied in recent years. They have excellent property of thermostability, inoxidizability, thermal shock resistance and thermal conductivity. So they are widely used in Aluminum melting field.Aimed at three typical components, by composition design and mould design, Si₃N₄ and Si₃N₄/SiC ceramics with high performance were prepared by Cold Isostatic Pressing (CIP) and reactive sintering, Microstructure, phase composition and mechanical property were investigated by methods of three-point bending, XRD, SEM and EDS, et al. The thermal shock test was carried out in a temperature range from 800℃ to room temperature. The main research contents and conclusions are as follows:(1) A series of Si₃N₄/SiC composites were prepared by Cold Isostatic Pressing and reactive sintering with industrial Si and SiC powder. The proportions of SiC powder in the initial mixtures were 10%, 30%, 50% and 70%, respectively, while the amount of phenolic resin adhesive (6.5wt% of the powder mixture) was kept constant. The results obtained showed that, as SiC addition increased in the initial mixture, the density of the sintered samples decreased from 2.41g/cm³ to 2.23 g/cm³ while the open porosity increased from 17.6% to 28.8%. The flexural strengths at room temperature were 109MPa, 92MPa, 63MPa å’Œ37MPa, respectively. These materials were thermal-shock resistant. The strength retained 78%, 104%, 106% and 89% of their room temperature values respectively, after 50 times thermal shocks form 800℃ to room temperature. The Si₃N₄ presents in form of equiax grain and acicular grain. The nitride ratio rises with the increase addition of addition.(2) A series of Si₃N₄ ceramics were prepared by Cold Isostatic Pressing and reactive sintering with industrial Si and α-Si₃N₄ powder. The proportions of α-Si₃N₄ powder in the initial mixtures were 10%, 20%, 30 and 40%, respectively, while the amount of PVA adhesive was kept constant. The results obtained showed that, as α-Si₃N₄ powder increased in the initial mixture, the density decreased from 2.27 g/cm³ to 2.04g/cm³ while the open porosity increased from 23% to 33.8%. The flexural...