Synthesis of clean aluminide coatings on Ni‐based superalloys via a modified pack cementation process

Abstract

With the aim of seeking a modified pack cementation process as a potential low‐cost alternative to form clean and reproducible aluminide coatings for laboratory diffusion coating research, four non‐contact arrangements were employed to coat Ni‐based superalloy specimens. The advantages and disadvantages of each arrangement were discussed by comparing the cleanliness of coating surface, the homogeneity of surface Al content and coating thickness, as well as the easiness of preparation. By utilizing the arrangement with the best overall quality, an Ni‐rich β‐NiAl coating with a clean surface and a low S level (0.3 ppmw) was achieved, which was comparable to the coatings previously made by an ultra‐clean laboratory chemical vapor deposition (CVD) process. Reactive element (RE) additions such as Hf, Zr, or Y were codeposited by including a small amount of the respective RE oxide in the pack mixture, and approximately 500 ppmw Hf was detected in the Hf‐modified NiAl coating.