Coated metal article

A coated article adapted to operate at temperature above 1000.degree. C. in an oxygen-containing environment, said article comprising a superalloy substrate, the superalloy being selected from the group consisting of nickel-based, cobalt-based, chromium-based, and iron-based alloys, and a coating forming an oxygen barrier over the superalloy surface, the coating exhibiting a close match in coefficient of thermal expansion with that of said superalloy and comprising a glass-ceramic having a composition, on an oxide basis in weight percent, selected from the group consisting of a barium silicate system and a strontium silicate system, the barium silicate system being essentially free from R.sub.2 O and B.sub.2 O.sub.3 and containing 20-65% BaO and 25-65% SiO.sub.2, the strontium silicate system being essentially free from B.sub.2 O and B.sub.2 O.sub.3 and containing 20-60% SrO and 30-70% SiO.sub.2, each system additionally consisting essentially of at least one oxide selected from the group consisting of up to 15% Al.sub.2 O.sub.3, up to 15% ZrO.sub.2, up to 15% Y.sub.2 O.sub.3, up to 25% MnO, up to 25% NiO, up to 30% MgO, up to 30% CoO, and up to 40% iron oxide, the total of all such additions not exceeding 50% in the barium silicate system and not exceeding 40% in the strontium silicate system, wherein the glass-ceramic in the barium silicate system contains a primary crystal phase selected from the group consisting of a barium silicate-type and cristobalite and the glass-ceramic in the strontium silicate system contains a primary crystal phase selected from the group consisting of a strontium silicate-type and cristobalite, in each system there being cristobalite crystals concentrated adjacent to the interface between the glass-ceramic and the superalloy.