Abstract: A process for forming an aluminide coating system on a substrate. The process includes preparing a slurry including, by weight, about 35 to about 65% of an aluminum donor powder, the aluminum donor material comprising at least 35% aluminum, about 1 to about 25% of a binder, and balance essentially carrier. The slurry is applied to the substrate. The substrate is a nickel or cobalt based superalloy being essentially free of aluminum. The slurry is heated to form an aluminide diffusion coating including an additive aluminide layer and an interdiffusion zone disposed between the substrate and the additive aluminide layer.