Interdiffusion kinetics of yttria and alumina

The interdiffusion kinetics of yttria‐alumina diffusion couples produced by spark plasma sintering (SPS) were investigated at 1350°C, 1425°C, and 1500°C. The SPS diffusion couples were heat‐treated in air at their sintering temperatures for 0, 24, and 96 h. Scanning electron microscopy (SEM) revealed the formation of yttrium aluminum garnet (YAG), yttrium aluminum perovskite (YAP), and yttrium aluminum monoclinic (YAM) interdiffusion layers at all temperatures, in agreement with the existing phase diagram. The thickness of each interlayer was measured as a function of exposure temperature and time to determine the apparent enthalpy and kinetics for interdiffusion. The interlayer growth followed parabolic kinetics, indicating diffusion‐controlled reactions. Furthermore, a Pt marker experiment demonstrated that the diffusion of Y 3+ ions toward the Al 2 O 3 side of the interface resulted in the formation of the YAG interlayer. In contrast, the diffusion of Al 3+ ions towards the Y 2 O 3 side of the interface caused the formation of the YAP and YAM interlayers. The thickness of the YAG interlayer was the highest among all interlayers, revealing rapid interdiffusion of Y 3+ ions through the YAG interlayer, compared to the Al 3+ ion diffusion through the YAP and YAM interlayers.