Study on Fabrication of MgAlON Transparent Ceramic

Abstract: MgAlON ceramic material is a new transparent ceramic, which developed from the AlON transparent ceramic recently. It has the same crystal structure, similar lattice parameter and better thermostability at low temperature compared with AlON. High density MgAlON transparent ceramics exhibit excellent mechanical and optical performance, especially in the region of 0.25~6μm wavelength, which is potential to be used in many fields.In this thesis, solid reaction process was employed to prepare high purity, fine-grained, and homogeneous dispersed MgAlON powders, which can meet the requirement of sintering. Firstly, the mixture ratio of the raw powders were designed according to the relationship between composition and vacancy concentration (site friction), and the phase diagram of MgO-AlN-Al2O3.Whereafter the effects of temperature, holding time, heating rate, atmosphere and mixture ratio on the phase and microstructure of synthesized powders were investigated systematically.We optimized the process and the mixture ratio for synthesizing high quality MgAlON powders. Finally, the relationship between microstructure and composition of the powders were established.Presureless sintering was adopted to prepare the MgAlON transparent ceramic. We examined the influence of sintering temperature and composition on the microstructure and transparency of MgAlON.The results showed that the MgAlON transparent ceramics, which was prepared at 1900℃,holding 24h, has highest quality. It has relative density of 99.98%, maximum real in-line transmittances of 42% (thickness is lmm) in the region of 0.25-6μm wavelength, and hardness of 13.3±0.82GPa. The microstructures of the sintering bodies are dense, low porosity, without second phase.And the grain sizes are very large with homogeneous distribution.For attaining transparent MgAlON ceramics in fine-grained and good mechanical, we tried to prepare them by rapid sintering method (SPS).The microstructure and transmittances depending on the sintering temperature, heating rate, holding time, and pressure were investigated. The result showed that the optimized process parameter is 1600℃,holding 1min,100℃/min, and 60MPa. The transparent ceramic obtained in this process has 99.54% relative density,72% real in-line transmittances in infrared red region and 14.17±0.30GPa hardness.The microstructure analysis showed that the sintered bodies were almost full dense, without second phase. And the grain size is about 1.5μm with homogeneous dispersion. Owing to the advantage of high heating rate and short heating time, the samples obtained by SPS have smaller grain size and higher hardness compared to pressureless sintering ones.
Key words: MgAlON; Solid reaction; Pressureless Sintering; SPS; Microstructure; Property;

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