High temperature phase stability and chemical analysis of the highly doped yttria stabilized zirconia with alumina

Short and long term thermal stability of YSZ was studied considering the equilibrium and non-equilibrium phase transformation of YSZ. To improve the long term thermal stability of YSZ, electrical treatment was introduced. Electrical treatment consists of applying electric field into YSZ at high temperatures under a reducing atmosphere. By optimizing the conditions of treatment, electrical resistivity reduced around 40% and thermal stability improved dramatically. These improvements are due to the generation of tetragonal metastable phases. Arguments are put forth to show that electrical treatment induces a relaxation in the lattice. This relaxation is associated with a reduction in lattice tetragonality and replaces the tetragonal grains of YSZ with domain of metastable phases. High resistance of metastable phase to creep deformation and lower electrical resistivity of domains of metastable phases in comparison with tetragonal grains brings about these improvements.