Preparation Of AlON Power And Hot-pressed Sintering Behavior Of AlON Ceramic Material

Spinel-structure aluminium oxynitride (AlON) is a pure and stable solid state ceramics in the Al2O3-AlN system. AlON has become the advanced and potential ceramic materials, because of its good mechanical, chemical and optical properties.In this study, AlON powder was successfully prepared by Al2O3 and AlN as raw material in N2 gas. The influence of raw material composition ratio, sintering temperature, holding time and different crystal on the powder preparation were studied respectively. The results show that the best mass ration of Al2O3 and AlN in raw material is 81:18. And the sintering process is at 1750℃for heat preservation for 2h, which the content of AlON phase is over 95%. Different crystal of Al2O3 had little influence on the content of sintered AlON.Two kinds of sintered AlON powder byα-Al2O3 andγ-AlON were used to prepare AlON single phase ceramic material by hot pressing technology under different temperature. The influence of hot pressing temperature on sintering densification of AlON single phase ceramic material was also studied. The results showed that under nitrogen atmosphere, the bulk density of AlON ceramic was increased and the open-porosity was decreased with the increasing hot pressure temperature, when the pressure was singly increased to 25MPa and heated preservation for 40min. When the hot pressure temperature reached to 1850℃, the bulk density and the open-porosity of AlON ceramic can be reached to 3.5g/cm3 and 1% respectively. Then the change was no longer obviously. The AlON powder sintered byα-Al2O3 had higher sintering activity than sintered byγ-AlON. Under the same hot pressure condition, the bulk density of AlON ceramic sintered byα-Al2O3 was bigger than sintered byγ-AlON in the low temperature. But when the hot temperature was 1900℃, the hot pressure sintered density of these two kinds of powder were almost the same and they all can be reach to 99%.Finally, the influence of the SiC content on the densification behavior, mechanical properties and fracture morphology of AlON/SiC ceramic matrix composites were all studied. The results showed that the bulk density and hardness of composite showed decrease trend with the increasing content of SiC. The flexural strength increased initially as the increasing content of SiC and then decreased. The best properties of composite can be arrived when the content of SiC is 8%. And the bulk density was 3.37g/cm3. The hardness was 18.49GPa. The flexural strength was 310MPa.The addition of SiC changed the fracture mode of AlON. The main fracture way of composite was changed from intergranular fracture to transgranular fracture and finally both of the two modes of fracture occurred. The main mechanism for SiC enhancing the strength of AlON/SiC composite was the mismatch of thermal expansion and strengthening resulted by grain refinement.