Study On Fabrication And Properties Of AlON Transparent Ceramics

Spinel-structure aluminium oxynitride (AlON) is a pure and stable solid state ceramics in the Al₂O₃-AlN system. AlON has become a new and potential type material, because of its good optical, mechanical and chemical properties. In this paper, SPS was selected to rapidly and successfully sinter transparent AlON ceramics.It was found that pure AlON phase could be synthesized when the Al₂O₃ and the A1N mole ratio was 68:32. Experiment condition: without any sintering aids, sintered at 1700℃, at a pressure of 30MPa, with heat rate of 100℃/min for 10min, in vacuum of 6Pa.The samples were sintered for 5min, 10min, 15min, and 20min. The measured relative density ranged between 98.01 and 99.3%, demonstrating that high density could achieve just for 5min. Density and hardness became a little higher and a little grain growth was found with the prolong of soaking time.The samples were sintered with heating rate of 50℃/min, 100℃/min, 150℃/min, and 200℃/min. The measured relative density ranged between 98.7-99.3%, demonstrating that SPS technique could short consolidation process and could achieve quick sintering. The highest density and hardness were achieved when the heating rate was 100℃/min.The samples were sintered at pressure of 10MPa, 20MPa, 30MPa, and 40MPa. The measured relative density ranged between 98.1 and 99.3%. Density and hardness increased with the sintering pressure, and reached the highest when the pressure was 30MPa.The samples were sintered in N₂ of 0.35×10⁵Pa. The fracture SEM micrographs of AlON ceramics showed that grains grew better in vacuum than in N₂ atmosphere.The study on the transparent mechanism and transmission factors of transparent ceramics indicates that the absorption, reflectivity and scattering all have effect on the transmittance of transparent ceramics. And the most important factor is scattering coefficient, including pores, secondary grain boundary phase and impurities phase. The samples were transparent after coarse-grinded, fine-grinded and polished to 0.5 mm thickness. The samples were transparent in wavelength ranged from 0.2～8μm The maximum transmittance was changed with soaking time, heating rate, and sintering temperature pressure. It was found that the maximum transmittance increased with prolong of soaking time, slow of heating rate, and higher sintered pressure.TEM observation displayed consolidated and uniform structure, which contributed to transmittance of AlON transparent ceramics. From TEM micrographs, dislocation, inter granular pores, pores in crystals and secondary grain boundary phase were also observed, which were adverse to transmittance of AlON transparent ceramics.