Multifunctionally graded environmental barrier coatings for silicon-base ceramic components

A multilayer article comprising:

• a substrate comprised of a silicon-base ceramic selected from the group consisting of silicon carbide, silicon nitride, silicon carbide/silicon carbide ceramic matrix composites and combinations thereof;
• a bond coat in contact with said substrate, said bond coat selected from the group consisting of, mullite doped with gadolinium oxide present from 0.5 to 10 molar percent, mullite doped with yttrium oxide present from 0.5 to 10 molar percent, mullite doped with ytterbium oxide present from 0.5 to 10 molar percent and combinations thereof;
• an interlayer comprised of a plurality of sublayers external to said bond coat, said sublayers comprised of chemically distinct layers wherein the thermodynamic activity of silicon within any given sublayer is less than the thermodynamic activity of silicon in an adjacent sublayer nearer in distance to said bond coat, said plurality of sublayers selected from the group consisting of, mullite doped with gadolinium oxide present from 0.5 to 10 molar percent, mullite doped with yttrium oxide present from 0.5 to 10 molar percent, mullite doped with ytterbium oxide present from 0.5 to 10 molar percent and combinations thereof;
• and
• a thermal barrier coating outer layer, said outer layer comprised of a base majority component, a first dopant oxide, at least one small rare earth oxide, at east one large rare earth oxide and at least one toughening oxide;
• said base majority component selected from the group consisting of an oxide of zirconium, hafnium and combinations thereof;
• said first dopant oxide selected from the group consisting of an oxide of yttrium, dysprosium, erbium and combinations thereof, said dopant oxide present from 1 to 10 molar percent;
• said at least one small rare earth oxide selected from the group consisting of an oxide of ytterbium, holmium, lutetium and combinations thereof, said small rare earth oxide present from 0.5 to 4 molar percent;
• said at least one large rare earth oxide selected from the group consisting of an oxide of neodymium, samarium, europium, gadolinium and combinations thereof, said large rare earth oxide present from 0.5 to 4 molar percent;
• and
• said at least one toughening oxide selected from the group consisting of an oxide of titanium, tantalum, niobium, scandium and combinations thereof, said toughening oxide present from 1 to 20 molar percent.