1416 A G. Evans et al Joumal of the European Ceramic Sociery 28(2008)1405-1419 (a)2500 (F) E0E°g四 13YSZ 1500 SZ Toughened ronia 主 90s mole %YO1.5 tria Content( mol% Y203 +YT+ZT able in the YSZ system. for the growth stress which, while measurable, has not been dequately rationalized or predicted (ii)a basic understanding of the adhesion of the a-AlO3/y-Ni interface is progressing. First principles computations based on density functional theory have demonstrated trends in the work of separation of the interface, To. upon segregation of 30 impurities and dopants, consistent with experimental find- mole %YO1.5 ings. A scheme for linking To to the toughness through a crack extension simulation is in place: but results are Fig. 16(a)ZrO2-YOis phase diagram showing the domain wherein not yet formalized because of ambiguities regarding the transformable-tetragonal solid solutions are thermodynamically feasible and plasticity length scale for the bond coat adjacent to the favored over the cubic form of the same composition up to 1300C(hatched Co(t/m) interface (iii)The toughness of tetragonal oxides has been attributed to of the To(F/)surface on the 1300 C isotherm Adapted from Ref [24 their ferroelastic properties. The dissipation that causes toughening occurs through nano-scale domain formation stive hat provide further measurements while attached to the toughness on the tetragonality, c/a, and the coercive stress substrate and characterize trends with inter -columna An ensuing focus on compositions in the Zro2-YO1.5-T1O connectivity are merited system having larger c/a has, indeed, led to a doubling of (v) Yielding of YSz contributes significant to its ability the toughness while consistent with the ferroelastic mech to withstand impact by projectiles at high temperature anism, direct evidence has yet to be provided. Moreover, Plastic deformation also participates in kink band devel such enhancements suggest that systems with yet larger opment during impact. A systematic assessment of the oughness compositions remain to be discovered. deformation mechanisms and of trends in yield strength (iv) Direct measurements of the in-plane modulus of the Ysz with composition would facilitate design for impact coatings generated by EB-PVD are still sparse. Approaches1416 A.G. Evans et al. / Journal of the European Ceramic Society 28 (2008) 1405–1419 Fig. 15. The toughness of monolithic ceramics showing the wide range achiev￾able in the YSZ system. for the growth stress which, while measurable, has not been adequately rationalized or predicted. (ii) A basic understanding of the adhesion of the -Al2O3/-Ni interface is progressing. First principles computations based on density functional theory have demonstrated trends in the work of separation of the interface, Γ 0, upon segregation of impurities and dopants, consistent with experimental find￾ings. A scheme for linking Γ 0 to the toughness through a crack extension simulation is in place: but results are not yet formalized because of ambiguities regarding the plasticity length scale for the bond coat adjacent to the interface. (iii) The toughness of tetragonal oxides has been attributed to their ferroelastic properties. The dissipation that causes toughening occurs through nano-scale domain formation during crack extension, suggestive of a dependence of toughness on the tetragonality, c/a, and the coercive stress. An ensuing focus on compositions in the ZrO2–YO1.5–TiO2 system having larger c/a has, indeed, led to a doubling of the toughness. While consistent with the ferroelastic mech￾anism, direct evidence has yet to be provided. Moreover, such enhancements suggest that systems with yet larger toughness compositions remain to be discovered. (iv) Direct measurements of the in-plane modulus of the YSZ coatings generated by EB-PVD are still sparse. Approaches Fig. 16. (a) ZrO2–YO1.5 phase diagram showing the domain wherein non￾transformable-tetragonal solid solutions are thermodynamically feasible and favored over the cubic form of the same composition up to 1300 ◦C (hatched area). (b) Extension of that domain into the ZrO2–YO1.5–TiO2 system. C0(t/m) is the trace of the T0(t/m) surface at ambient temperature, and C0(F/t) is the trace of the T0(F/t) surface on the 1300 ◦C isotherm. Adapted from Ref. [24]. that provide further measurements while attached to the substrate and characterize trends with inter-columnar￾connectivity are merited. (v) Yielding of YSZ contributes significant to its ability to withstand impact by projectiles at high temperature. Plastic deformation also participates in kink band devel￾opment during impact. A systematic assessment of the deformation mechanisms and of trends in yield strength with composition would facilitate design for impact tolerance.