A thermally protective coating (21), such as may be used over a nickel-based superalloy substrate (24). The protective coating (21) includes a CoNiCrAlY or a NiCoCrAlY material and addition of given amounts of one or more secondary elements. The secondary element(s) facilitate and/or join in one or more precipitation mechanisms (γ′, B2) that retain an aluminum reservoir in the protective coating (21), reducing aluminum diffusion into the substrate (24). This aluminum reservoir maintains a protective alumina scale (38) on the coating (21), thus improving coating life and allowing higher operating temperatures.