Study On High Temperature Hot Pressing Sintering Process And Properties Of AlN Ceramics

AlN ceramics have various excellent properties,especially high thermal conductivity and low dielectric properties,which make it widely used in many fields such as electronic substrate packaging materials and heat-resistant materials.In the market,atmospheric sintering process is often used to prepare AlN ceramics.However,the performance of AlN ceramics prepared by this sintering process is poor.If sintering body with high thermal conductivity is to be prepared,high sintering temperature and long holding time are needed,which will lead to high cost.Therefore,in order to prepare AlN ceramics with higher thermal conductivity and reduce the production cost.In this paper,the hot pressing sintering process is used to prepare AlN ceramics,and the influence of sintering process parameters on the microstructure and properties of pure AlN ceramics and AlN ceramics with sintering additives is studied.The research contents are as follows:（1）The effects of different sintering temperatures,sintering pressures,prepressing pressures and holding time on the microstructure and properties of pure AlN ceramics were studied under the conditions of nitrogen atmosphere and prepressing time of 30min without any sintering additives.The results show that at 1800～1900℃,with the increase of sintering temperature,the density and thermal conductivity of AlN ceramics increase rapidly,AlN grains grow rapidly,and the number of pores decreases.When the sintering pressure is 30～50MPa,with the increase of the sintering pressure,the grain size of AlN slowly increases,the porosity decreases continuously,and the density and thermal conductivity also increase significantly.When the precompression pressure is between 30 MPa and 50MPa,with the increase of the precompression pressure,the AlN grains gradually become smaller,the porosity decreases continuously,and the grain boundary becomes clear,so that the density and thermal conductivity also increase significantly.When the holding time was 3～5h,with the increase of the holding time,the porosity shrank and significantly decreased,but the grain growth was too large and irregular,leading to the indistinct grain boundary,so that the density gradually increased,but the thermal conductivity showed a trend of first increasing and then decreasing.Under the conditions of sintering temperature of 1850℃,sintering pressure of 40MPa,prepressing pressure of 50MPa and holding time of 3h,the composite performance of AlN ceramic sintered body is the best.（2）AlN powder prepared by direct nitriding method was used as raw material,and 5wt%（mass fraction）of Y₂O₃was added as sintering assistant.The effects of different sintering atmosphere,sintering temperature,pressure and prepressing time on the microstructure and properties of AlN ceramics were studied when the prepressing pressure was 40MPa and the holding time was 2h.The results show that,compared with vacuum atmosphere,the grain growth of AlN ceramics prepared in nitrogen atmosphere is more complete,and the pore between grains is relatively less,which makes the thermal conductivity and density of AlN ceramics higher.When the sintering temperature is between 1700℃and 1900℃,with the increase of temperature,the grain size of AlN ceramics grows and the grain boundary phase gradually concentrates at the triangular grain boundary.The thermal conductivity and density both increase first and then decrease.Sintering pressure in 30～50MPa,with the increase of pressure When the size of AlN is large,the grains of AlN become small and compact,and the pores between grains become less,so that the density and thermal conductivity of AlN are greatly improved.When the prepressing time is 10～30min,with the increase of the prepressing time,the AlN particles bond more closely before sintering.After sintering,the crystal form of AlN ceramics is gradually full,the porosity decreases,and the thermal conductivity and density are significantly increased.AlN ceramics sintered in nitrogen atmosphere,sintering temperature 1800℃,pressure 40MPa and prepressing time 30min have the best comprehensive properties.