Research on the reaction synthesis of AlN-based ceramics with the addition of Y₂O₃

Compact AlN/Y₂O₃ ceramic was fabricated by combustion synthesis of Al particles in the ultra-high pressure nitrogen (1000 MPa). The SHS reaction procedure of the Al-N₂-Y₂O₃ system is as follows: Al melts at 660 °C, volatilizes strongly at 1000 °C and rapidly reacts with N₂ to form AlN , meanwhile a great deal of reaction heat is released out; When the temperature is up to 1760 °C, eutectic melt Al₅Y₃O₁₂ form from Y₂O₃ and Al₂O₃, then liquid sintering occurrs. Liquid sintering at high temperature decreased the porosity of reaction zone and greatly improved relative density of products. However, high relative density made reaction ratio decrease and residual Al content increase in the products, because it was more difficult for N₂ to penetrate to the reaction zone. With increasing of Y₂O₃ content in the original powder system, porosity of the products decreases, content of Al in the products increases, and the bending strength and fracture toughness are improved. In Al-N₂-Y₂O₃ system, SHS-densification mainly occurrs along the combustion front.