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Research and Application of Aluminum Nitride Ceramics

wallpapers News 2021-11-19
Research and Application of Aluminum Nitride Ceramics
Aluminum nitride (AlN) has attracted more and more attention in the field of new materials due to its high thermal conductivity, low dielectric constant, thermal expansion coefficient matching with silicon, and other excellent physical properties. This article mainly introduces and analyzes AlN The latest trends and developments in powder synthesis, sintering technology, and basic theories of application, as well as the application fields and prospects of AlN ceramics.
High thermal conductivity, machinable AlN/BN composite ceramic is a new type of composite material with great application prospects, which can be used as an ideal material for applications in the field of microelectronics, microwave transmission equipment, and high-temperature corrosive environments. However, AlN and BN are both covalent bond compounds with high melting points and low self-diffusion coefficients. In the Al-BN system, AlN and BN have different crystal structures and valence electron structures, and cannot form a solid solution under equilibrium conditions; at the same time, During the sintering process, the growth of h-BN flake crystals will form a card house structure, which hinders the sintering shrinkage and densification of the material. These factors make the complete densification of AlN/BN ceramics a technical problem and affect the performance of the material.
Spark plasma sintering (SPS) technology is a material preparation method far from the equilibrium state. It has high production efficiency, dense and fine structure of the prepared material, and can realize the control of the phase composition and structure of the material.
The paper studied the densification process and mechanism of AlN ceramics and AlN/BN composite ceramics and discussed the influence of sintering aids on the microstructure and thermal conductivity of AlN ceramics. The focus is on the microstructure, thermal conductivity, and workability of SPS sintered AlN/BN composite ceramics, and the use of powder synthesis and grain boundary phase purification processes to control and adjust the structure and performance of AlN/BN composite ceramics to keep them in good condition On the basis of processability, it has high thermal conductivity.
The pure AlN powder can obtain a sintered body with a density of more than 97.5% when the holding time of pure AlN powder is extended to 15 minutes at 1900°C or 1850°C. The addition of Y2O3, Sm2O3, and Li2O can significantly promote the sintering of AlN ceramics, reduce the sintering temperature of the powder, increase the density of the sintered body, and significantly improve the thermal conductivity of the sample. The thermal conductivity of the sample with 1.5wt% Sm2O3 can reach 150W/m·K. The type of sintering aid affects the distribution of grain boundary phases in AlN samples, crystal growth, and the combination of AlN grains, and affects the thermal conductivity of AlN ceramics through these microstructure factors.
AlN/BN micro-composite ceramics can be densified by SPS at 1700~1800℃. Since the SPS sintering is completed in a very short time, the growth of flake h-BN crystals does not significantly hinder the densification of the sample. The AlN/30vol% BN sample can also reach a relative density of 98.3%. Moreover, the SPS sintered AlN/BN composite ceramics have a uniform microstructure, and the h-BN grains do not appear to be aligned.
The BN phase inhibits the growth of AlN grains, and the microstructure is refined so that the introduction of a small amount of BN phase does not lead to a decrease in the mechanical strength of the material. However, with the increase of BN content in AlN/BN micro-composite ceramics, the mechanical strength decreases, and the thermal conductivity, microhardness, elastic modulus, and fracture toughness of the material also show a downward trend. However, due to a lot of decrease in microhardness, The machinability of the material is enhanced, and samples containing 10-15 vol% BN can be processed with cemented carbide tools.
 

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