Surface morphology of diffusion aluminide coatings

The surface structure and morphology of aluminide coatings can be important in their performance both in oxidation or hot corrosion resistance and in their mechanical behavior. However, little information is available on the effects of aluminide coating deposition conditions on the coating surface. A study of the effects of aluminide processing parameters on both pure nickel and a nickel-base superalloy, IN 738, revealed a systematic change in surface morphology from a rough, serrated, fine-grain surface which occurs with a high aluminum activity deposition process to a smooth coarse-grain structure for the low aluminum activity process. A systematic change in coating color was also observed for both the pure metal and the alloy with changing coating aluminum contents. Results are reported and related to the coating phases present during the deposition process.