Investigation on properties and microstructure of reaction-sintered Si3N4 ceramics
Comparative experiments have been conducted using static air pressure and flowing nitrogen atmosphere to explore the influence of the silicon powder mass fraction in reaction-sintered Si3 N4 ceramics on the nitridation rate and mechanical properties of Si3 N4 ceramic materials.It is found that the nitridation rate could reach 97％ at a nitrogen pressure of 2 MPa,which is significantly higher than that of the flowing nitrogen atmosphere ( 91％) .It illustrates that the higher gas pressure is more conducive to the diffusion and nitridation reaction when using static nitrogen.At the same time,SEM and other methods have been used to observe the static air pressure reaction sintering of Si3 N4 ceramic and found that when the mass fraction of silicon powder is greater than 10％,pores appear on the surface of Si3 N4 ceramic.This is because as the mass fraction of Si powder increases,the Si powder migrates and aggregates in the molten state,resulting in a decrease in the Vickers hardness and flexural strength.
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