Ferroelastic domain switching toughening in spark plasma sintered t’-yttria stabilized zirconia/La2Zr2O7 composite ceramics

The poor fracture toughness of La 2 Zr 2 O 7 hinders its practical application as a thermal barrier coating topcoat material. To toughen La 2 Zr 2 O 7 , metastable tetragonal 8   wt% yttria-stabilized zirconia ( t ’-8YSZ), has been introduced into the La 2 Zr 2 O 7 matrix by plasma spray quenching of 8YSZ powders and spark plasma sintering . An evident fracture toughness improvement has been achieved due to ferroelastic domains switching. The resulting toughness increase has a quadratic relationship with t ’ phase volume fraction below a critical value (30   vol%), beyond which it is far smaller to what expected owing to the residual stress being smaller than the ferroelastic coercive stress.