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Silicon Nitride Ceramics with High Thermal Conductivity and Excellent Mechanical Properties Fabricated with MgF₂ Sintering Aid and Post-Sintering Heat Treatment

F. Hu, F. Hu, L. Zhao, Z.P. Xie

Journal of Ceramic Science and Technology, Vol. 7, No. 4 (2016), pp. 423-428

DOI: 10.4416/JCST2016-00065

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Abstract

Si3N4 ceramics were prepared with MgF2+Y2O3 as sintering aids by means of SPS, assisted by post-sintering heat treatment; these ceramics exhibited high thermal conductivity and excellent mechanical properties. The effect of the introduced MgF2 content and post-sintering heat treatment on the properties of Si3N4 ceramics was investigated in detail. It was found that the introduction of MgF2 had a positive impact on the growth of large elongated grains and the grain size of the Si3N4 ceramics. Compared to Si3N4 ceramics with Y2O3+MgO as sintering aids, the thermal conductivity, flexural strength and fracture toughness of the Si3N4 ceramics with Y2O3+MgF2 as sintering aids were increased by ∼ 19 %, 9 % and 12.7 %, respectively. After post-sintering heat treatments, the thermal conductivity and fracture toughness of the Si3N4 ceramics were increased by ∼ 29.9 % and 16.2 %, respectively. However, the flexural strength of the Si3N4 ceramics was reduced by ∼ 10 %. The resulting Si3N4 ceramics exhibited possessed thermal conductivity of 82.5 W·m-1·K-1, flexural strength of 911 MPa and fracture toughness of 8.47 MPa·m1/2.

Keywords

MgF2 sintering aids, silicon nitride, thermal conductivity, mechanical properties

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