Effects of Y2O3 and Al2O3 sintering additives on the hot pressing behavior of AlN ceramics

Abstract AlN plates were fabricated by hot pressing AlN-Y 2 O 3 and AlN-Y 2 O 3 -Al 2 O 3 powder mixtures at 1700–1900 °C using yttria and alumina (Al 2 O 3 particle sizes of 3 and 10 μm) powders as sintering additives. The physical and mechanical properties of the hot-pressed AlN ceramics were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The density, thermal conductivity, transverse rupture strength, and grain size were measured. The thermal conductivity of the hot–pressed AlN ceramics ranged between 83–92.7 W × (m × K) −1 and decreased with the addition of Al 2 O 3 , whereas the mechanical properties improved with the addition of Al 2 O 3 , which is known to have a beneficial effect of grain size refinement. The measured density values of 3.31 to 3.34 g × cm −3 were slightly higher than the theoretical density of 3.26 g × cm −3 . This result was attributed to the use of a carbon mold under N 2 atmosphere, which effectively removed oxygen atoms from the yttrium-aluminate phase that is expected to form at 1100 °C.