Abstract: The present invention provides a protective coating for a gas turbine blade or other component wherein the duplex coating includes an aluminum-bearing coating, such as a diffusion aluminide, formed on a first, relatively higher temperature region of the blade/component and a later-applied chromium-bearing diffusion coating formed on an adjacent relatively lower temperature region of the blade/component subject to hot corrosion in service. The chromium-bearing coating is applied after the aluminum-bearing coating by masking that coating and depositing a metallic chromium coating on the adjacent region followed by diffusing the chromium into the blade/component alloy to form a chromium-enriched diffusion coating thereon.

Abstract: A multi-wall ceramic core for casting an airfoil with one or more internal cooling passages is made by preforming at least one fugitive core insert to have a joint-forming surface with a male and/or female joint feature and then forming at least one fugitive core insert in-situ adjacent and integrally connected and fused to the at least one preformed core insert at the joint-forming surface to form an interlocked, fused joint to form a composite core insert that includes features to form internal passage surfaces in the core when the composite core insert is removed. Another aspect involves preforming first and second fugitive core inserts to have respective joint-forming surfaces with respective snap-fittable joint features and assembling the first and second fugitive core inserts to form a composite core insert by snap fitting the snap-fittable joint features together to form an interlocked joint.