Equilibrium Grain Boundary Segregation In CeO₂-doped 3Y-ZrO₂

Yttria-stabilized zirconia has been widely used as ceramic thermal barrier coatings. Because of its insulation effect, high melting point, low thermal conductivity and good chemical stability, it has great potential for applications as thermal barrier coatings.The thermal barrier coatings consists of ceramic surface coating and metal buffer layer (metal bonding layer), where oxygen pass through the ceramic pores, cracks and grain boundaries to penetrate into the buffer layer, leading to the formation of oxides(which mainly is Al₂O₃) between the ZrO₂ceramic buffer layer and the MCrAlY coating. The coating and substrate thermal expansion mismatch generates residual compressive stress in the oxide layers, which leads to coating cracking and spalling. With increasing the density of the ceramic coating, the oxygen pass through the grain boundary to penetrate into the buffer layer and then generates oxide,which has become a major reason for failure of the thermal barrier coatings.Some research demonstrated that Ce may suppress the transportation of oxygen atoms at grain boundary. But the grain boundary segregation of Ce was related to other elements of solute in material. In these work, the grain boundary segregation of Y and Ce in CeO₂doped 3Y-ZrO₂was studied, in order to find out the interaction between the grain boundary segregations of Y and Ce. The CeO2-doped 3Y-ZrO₂sintered at 1600 oC for 10 hours, then cooled to room temprature. In this condition, the sintered sample have the largest properation of intergranular fracture in fracture surface. The specimens were then holded at 960oC, 1020oC, 1080oC, respectively, to obtain equilibrium segregation. Using the Auger electron spectroscopy (AES), boundary concentration of Y and Ce were measured.According to the AES results, it is shown that the boundary concentration of Ce decreased with increasing tempreture, while the boundary concentration of Y increased with increasing tempreture. Finally, the machamism of equilibrium segregation of Y and Ce in CeO₂ doped 3Y-ZrO₂ was studied, indicating that it is the site-competition mechanism.