Study On The Property Of Pressureless Liquid Phase Sintering Silicon Carbide Ceramic

Silicon carbide ceramic has been used widely in the petrochemical, aerospace, mechanical seals, electronic packaging fields, as a structural ceramics wich has excellent performance of high-temperature, therefore, it has very important significance that carry out research the mechanical and thermal properties of Si C ceramic. Because of its easy preparation, low sintering temperature and excellent mechanical properties of products, pressureless liquid phase sintering has become a promising sintering technology. The reasonable choice sintering addition is an important researching content in the pressureless sintering technology.In this paper, α-Si C and β-Si C powders as matrix, added to La₂O₃-Y₂O₃, Al N-Y₂O₃-Mg O and Al N-Y₂O₃-La₂O₃-Mg O three kinds of sintering additions, respectively, 30 silicon carbide ceramics samples of 6 system were prepared by pressureless liquid phase sintering. And its phase composition, surface morphology, density, mechanical properties and thermal properties were measured and analyzed. The main findings are as follows:1)The results of Si C-La₂O₃-Y₂O₃ ceramic series showed that: With sintering addition content increasing, the density, relative density, hardness and thermal conductivity of the different proportions of α-Si C-La₂O₃-Y₂O₃ ceramics showing the same trends, thermal expansion coefficient is monotonically increasing trend. The density, relative density and hardness of the different proportions of β-Si C-La₂O₃-Y₂O₃ ceramic increased to the maximum and then decreased with increase of sintering addition content, the thermal expansion coefficient presented variation after first decreased and then increased. In all 10 samples, the α-Si C-La₂O₃-Y₂O₃ ceramic which has 9wt.% sintering addition get the best performance. Its density is 3.1169g/cm3, relative density is 93.13%, hardness is 1021.00kgf/mm2, thermal conductivity is 112.495W/（m·K） at 50℃, an average thermal expansion coefficient is 0.3181×10-6/K from-80℃ to 50℃.2)The results of Si C-Al N-Y₂O₃-Mg O ceramic series showed that: The change of sintering additives content have an obvious impact on density, hardness, thermal conductivity and thermal expansion coefficient of Si C-Al N-Y₂O₃-Mg O ceramic. The same proportion of the β-Si C-Al N-Y₂O₃-Mg O and α-Si C-Al N-Y₂O₃-Mg O ceramic, density and hardness compared to the latter is always better than the former, while the change of the thermal conductivity and thermal expansion coefficient is more complex. In all 10 samples, the maximum density and relative density of the α-Si C-Al N-Y₂O₃-Mg O ceramic which has 19.5wt.% sintering addition has a maximum value,density is 3.3481g/cm3, relative density is 98.8%. The α-Si C-Al N-Y₂O₃-Mg O ceramics which has 22 wt.% sintering addition get the maximum hardness of 1929.933kgf/mm2. The β-Si C-Al N-Y₂O₃-Mg O ceramic which has 17 wt.% sintering addition get the minimum thermal expansion coefficient of 1.51×10-6/K. The β-Si C-Al N-Y₂O₃-Mg O ceramic which has 22 wt.% sintering addition get the maximum thermal conductivity of 103.367W/（m·K） at 50℃.3)The results of Si C-Al N-Y₂O₃-La₂O₃-Mg O ceramic series showed that: When the quality percentage of sintering additives is 17.5%, α-Si C-Al N-Y₂O₃-La₂O₃-Mg O and β-Si C-Al N-Y₂O₃-La₂O₃-Mg O ceramics get the maximum density, relative density and hardness, density is 3.1764g/cm3 and 3.0555g/cm3, relative density is 92.16% and 86.76%, hardness is 1753.800kgf/mm2 and 2323.433kgf/mm2, respectively. When the quality percentage of sintering additives is 12%, the thermal expansion coefficient of α-Si C-Al N-Y₂O₃-La₂O₃-Mg O and β-Si C-Al N-Y₂O₃-La₂O₃-Mg O get the minimum of 1.4554×10-6/K and 0.2220×10-6/K, respectively. The thermal conductivity of the α-Si C-Al N-Y₂O₃-La₂O₃-Mg O ceramics which has 14.5wt.% sintering addition get the minimum value,it is 69.479W/（m·K） at 50℃. The β-Si C-Al N-Y₂O₃-La₂O₃-Mg O ceramics which has 12 wt.% sintering addition get the maximum thermal conductivity of 63.396W/（m·K） at 50℃.