Fabrication and oxidation of an Y2O3-modified low temperature aluminide coating on 309 stainless steel

By using Y2O3 nanoparticles, instead of part of Al2O3, acting as filler, Y2O3-modified aluminide coatings were produced on 309 stainless steel using a conventional pack-cementation method at 600 °C for 8 h. For comparison, normal aluminide coating was also produced using pure Al2O3 acting as filler. Effect of Y2O3 on the coating microstructure and oxidation resistance at 900 °C was comparably investigated. The results indicated that the entrapped Y2O3 particles not only significantly refined the grain of aluminide coatings but also promoted the formation of a dense, adherent and continuous α-Al2O3 layer. With the oxidation, the Y2O3 particles, after being swept by the inward-growing alumina scale, partially dissolves to produce Y cations. The segregation and migration of Y cations along the short-circuit path hinder the outward diffusion of Al, thus further decrease the scaling rate.