Abstract: An aluminiding process that enables the cooling holes of an air-cooled component, such as a hot gas path component of a gas turbine engine, to be machined and then aluminized after all external surface coatings have been deposited. The aluminide coating is deposited using a slurry process capable of forming the aluminide coating on the component without damaging an existing ceramic coating on the component. The process involves applying an activator-free slurry containing aluminum particles that, when the component is sufficiently heated, melt and diffuse into the component surface to form the diffusion aluminide coating.