Study On The Pressureless Sintering Of Transparent AlON Ceramics And Fast Densification Mechanism Based On The Particle Size Distribution

Transparent aluminum oxynitrde?AlON?ceramics is new kind of functional ceramics and have many excellent exproperties,such as robust mechanical strength,chemical attack resistance and high transparency in a vide-band?IR-U-V?,which is widely used in the special equipment,infrared detection and other fields,has a broad prospects for development.At present,transparent AlON ceramics can be fabricated by pressureless or hot pressing method in many countries.The high sintering temperature and long hoding time limit it from large scale commercial production.In this paper,AlON powder synthesized by carbothermal reduction and nitridation method and Y₂O₃?as the sintering aids?were used as the starting materials,and the AlON powders with different partical size distributions were obtained by planetary ball milling method with different parameters.One is the unimodal powders,D50 =1.1?m,the other is bimodal powders,the characteristic peak position is 1.1gm and 2.2?m respectively.Then,use the bimodal and unimodal powders sintered AlON transparent ceramics.It was found out that both the densification rate and the density at the same temperature of the bimodal powder were higher than that unimodal powder.The phase transformation of bimodal powders during pressureless sintering showed that the AlON powder changed to Al₂O₃ and AIN when the temperature was raised to 1400? and the coarse AlON particles transformed to cubic rl-Al₂O₃ and h-AIN,and the small AlON transformed to ?-Al₂O₃ and h-AIN,?-Al₂O₃ was transformed into AlON at a temperature between 1600 and 1700? and ?-Al₂O₃ was transformed into AlON between 1700 and 1800?,the lower phase transformation temperature of ?-Al₂O₃ to AlON is mainly benefited from the similarity in crystal structure between them.Further microstructural evolution studies have shown that:fast heating is favorable because it is helpful to keep near sphere bimodal grain size distribution during heating.The spherical particles is favorable for the rearrangement and the bimodal PSD is favorable for grain growth.The mass transport between large to large,large to small and small to small AlON grains can simultaneously happen during fast densification?after all Al₂O₃ was transformed into AlON?without the interception of small residual?-Al₂O₃.As a result,AlON grains grow rapidly and the pores can be eliminated effectively at the final stage of sintering to obtain a high-density samples.Finally,AlON powder with bimodal PSD was selected and sintered at 1880??fast heating at 40?/min?for 150 min.The infrared transmittance of AlON transparent ceramics with the thickness of 3mm was 81.8%.