Reaction bonding alumina with AlN–SiC solid solution by nitridation of matrix containing Al–Si powders

An AlN–SiC solid solution-bonded alumina composite was successfully synthesized by pre-synthesizing an isostructural AlN mesophase as an induced nucleus at 1600 °C in flowing nitrogen. The phase composition and morphology were characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The reaction mechanism is as follows. An AlN cladding is formed on the surface of Al particles by holding the Al–Si–Al2O3 green body at 580 °C for 8 h in N2 atmosphere. As the temperature rises, the AlN cladding ruptures, Al(l) flows out, and entraps the AlN fragments with high reactivity to migrate along the pores, mixing Si(l) and ultra-fine carbon from resin binder in the matrix to form an Al(l)–Si(l)–C(s)–AlN(s) mixture. At 1600 °C, Al(l) and Si(l) preferentially react with trace O2 in nitrogen to form metastable Al2O(g) and SiO(g), which diffuse outward and react with N2 in the peripheral of the brick to form a sheet-like 21R-SiAlON. The 21R-SiAlON sheets interlaced with each other, forming a dense layer. The formation of the dense layer rapidly consumes O2, and the $$P_{{{\text{O}}_{{2}} }}$$ inside the brick is lowered quickly. In such reducing condition, under the induction of the preformed AlN mesophase, the isostructural AlN–SiC solid solution is formed in situ by the reaction between Al(l)–Si(l)–C(s)–AlN(s) mixture and N2, and therefore a non-oxide bonded oxide composite is prepared. The AlN–SiC solid solution-reinforced Al2O3 composite possesses high cold crushing strength of 116–217 MPa.