Annealing of AlN guided by estimation on oxygen content

Abstract

In this paper, an estimation method revealing relationship between residual oxygen content and Y2O3 additive amount used in AlN sintering was presented. It is revealed that AlN sample added with 3 wt% Y2O3 showed better performance than the others while the oxygen content is 0.765 wt% in the initial powders. Nevertheless, short-time sintering does not make AlN to obtain ultra-high performance consistent with the estimation. By two-step sintering regimes, the distribution of second phase in AlN ceramic was changed from continuous distribution to island-like distribution significantly. The bending strength increases first and then decreases, reaching a higher value of 418 MPa after 2-h annealing. The residual oxygen content continues to decrease as more liquid second phase precipitated with long-time annealing. After reaching a state with lower residual oxygen content than the estimation, high-performance AlN is prepared with thermal conductivity of 230 W/m·K and lower bending strength of 358 MPa.