Phase reaction and sintering behavior of a Al 2O 3–20wt%AlN–5wt%Y 2O 3 system

Abstract

Two major problems exist in the processing of AlN. The first is the difficulty in achieving full densification even at relatively high sintering temperatures. The second is the formation of the spinel phase, AlON. Pure AlN sintered at temperatures up to 2000°C have produced no more than 90–93% densification in the former case, while AlN rich ternary systems (AlN–Al 2O 3-sintering agent) have resulted in the detrimental formation of AlON well before full densification can occur. This paper reports on the phase reaction and sintering behavior of a ternary Al 2O 3–AlN–Y 2O 3 system near the critical temperature range of 1600–1700°C, in a carbo-thermal reduction furnace in a fully nitrogen environment. Full densification (>98%) for AlN without the formation of AlON was achieved by sintering an initial Al 2O 3 rich ternary system (Al 2O 3–20wt%AlN–5wt% Y 2O 3) at a relatively low temperature of 1680°C. Formation of the AlON was delayed until 1700°C, at which a stoichiometric γ-AlON (Al 3O 3N) with spinel type structure was obtained. Thermal conductivity values for a sintered substrate obtained with low oxygen content within the AlN matrix reached 125 W m −1 K −1.