Sintering phenomena of reaction bonded silicon nitride were investigated to study the microstructural development by both densification and α/β phase transformation, and to study the interdependency between microstructures and mechanical strength.
Reaction bonded silicon nitride samples were prepared with an overall compact density of 66% with uniformly dispersed porosity. After infiltration of MgO into RBSN, sintering experiments were achieved at isothermal temperatures between 1650-1820℃.
Alpha-phases with high specific surface area, which were grown into pores of RBSN, soluted and transformed rapidly to beta-$Si_3N_4$ leaving large pores behind, before reaching the sintering temperature. But no development of β-prism was shown.
The α/β phase transformation was more rapid process than densification. However, it's rate was highly dependent on sintering temperature. Densification just after phase transformation decreased the porosity and increased the interlocking of β-prism, and so increased the mechanical strength.
Mechanical strength was markedly increased after sintering of RBSN, due to the interlocking of grown β-prisms.
