Microstructure and thermal conductivity of spark plasma sintering AlN ceramics

Abstract

Dense aluminium nitride ceramics were prepared by spark plasma sintering at a lower sintering temperature of 1700uC with Y 2 O 3 , Sm 2 O 3 and Dy 2 O 3 as sintering additives respectively. The effects of three kinds of sintering additives on the phase composition, microstructure and thermal conductivity of AlN ceramics were investigated. The results showed that those sintering additives not only facilitated the densification via the liquid phase sintering mechanism, but also improved thermal conductivity by decreasing oxygen impurity. Sm 2 O 3 could effectively improve thermal conductivity of AlN ceramics compared with Y 2 O 3 and Dy 2 O 3 . Observation by scanning electron microscopy showed that AlN ceramics prepared by spark plasma sintering method manifested quite homogeneous microstructures, but AlN grain sizes and shapes and location of secondary phases varied with the sintering additives. The thermal conductivity of AlN ceramics was mainly affected by the additives through their effects on the growth of AlN grain and the location of secondary phases.

Microstructure refinement - homogenization and flexural strength improvement of Al2O3 ceramics fabricated by DLP-stereolithography integrated with chemical precipitation coating process

“…Furthermore, the dispersive performance of additives (Y2O3) in Al2O3 matrix is expected to lead to the morphology change of second phases (yttrium aluminates), and the thermal conductivity of ceramics can be highly affected by the grain growth and the morphology of second phases, as commonly seen in AlN ceramic [41,42]. Nevertheless, this CP process has never been used for the preparation of stereolithography-based 3D printed Al2O3 ceramics.…”

“…Compared with the conventional MM process, the chemical precipitation coating (CP) process, which has been employed in the preparation of YAG, SiC and translucent Al2O3 ceramics [38][39][40], shows more homogeneous mixing performance and can improve the microscopic uniformity of ceramics. Furthermore, the dispersive performance of additives (Y2O3) in Al2O3 matrix is expected to lead to the morphology change of second phases (yttrium aluminates), and the thermal conductivity of ceramics can be highly affected by the grain growth and the morphology of second phases, as commonly seen in AlN ceramic [41,42]. Nevertheless, this CP process has never been used for the preparation of stereolithography-based 3D printed Al2O3 ceramics.…”

Effects of Grain Sizes and Impurities on Thermal Conductivity in Aluminum Nitride

“…As AlN has the ability to accommodate oxygen to levels exceeding 4 at. % [6], oxygen related defects are most important in the material, but the dynamic behavior of oxygen related defects on the thermal conductivity has not been clearly understood [7][8][9][10][11]. The scattering of phonons is also affected by the grain sizes, dislocations and other impurities in AlN ceramics.…”