Effects of reactive gaseous mixture and time on the growth rate and composition of aluminium diffusion coatings by CVD-FBR on 12Cr-ferritic steel

Aluminium deposition on ferritic steel HCM12 A (P-122) by chemical vapour deposition in a fluidized bed reactor (CVD-FBR) has been studied. A thermodynamic study of the partial pressures of the gaseous species present in the system during the CVD, was performed using the Thermocalc software. The coating obtained was studied by XRD, SEM and EDX. The influence of the HCl input ratio on the H2/HCl reactive gas mixture was investigated. It was found that with an increase of HCl input thicker coatings consisting of the Fe–Al intermetallic phase were formed. By increasing the deposition time the thickness of the Al-layer also increases and the Fe2Al5 and FeAl3 intermetallic phases are formed.