Development of aluminide diffusion coatings on ODS ferritic-martensitic steel for corrosion resistance in high temperature super critical-carbon dioxide environment

Aluminide diffusion coatings were applied on an oxide dispersion strengthened ferritic-martensitic (ODS-FM) steel as surface modification methods. Either thin layer of Al or NiAl was deposited on the ODS-FM steels, which were subjected to inter-diffusion heat treatment (IDHT) to produce Al-IDHTed or NiAl-IDHTed specimens, respectively. After corrosion test in high temperature super-critical carbon dioxide (S-CO2), both Al-IDHTed and NiAl-IDHTed specimens showed significantly improved corrosion resistance with lower weight gains and effectively supressed carburization in the matrix. The improvement in corrosion resistance was attributed to the presence of continuous alumina layer on top of surface layer. For Al-IDHTed specimen, extensive diffusion of Al from surface layer and inter-diffusion zone to substrate was observed after the S-CO2 corrosion test. However, for NiAl-IDHTed specimen, an Al-rich surface layer was well-maintained after S-CO2 corrosion as Ni acted as a diffusion barrier.