Papers by Keyword: CVD-FBR

Abstract: The steam oxidation behaviour at 800°C of aluminized HCM12A ferritic-martensitic steel has been studied. The aluminization process used was CVD in fluidized bed reactor (CVD-FBR), using a reactive bed modified with Ce or La particles. The obtained coatings were mainly composed of (Fe,Cr)2Al5 intermetallic phase. Long term oxidation (1000h) behaviour of the coated HCM12A was studied in 100%H2O atmosphere. By the application of the protective coating, the ferritic-martensitic steel oxidation rate is reduced considerably because of the alternately formation of Al2O3 and Cr2O3 + (Fe,Mn)3O4 protective scales on the substrate surface due to the diffusion processes that take place during the exposure at high temperatures in combination with the aggressive environment.

Abstract: In this work, iron aluminide coatings were developed by Chemical Vapor Deposition in Fluidized Bed Reactor (CVD-FBR) on ferritic-martensitic steels. Small additions of zirconium powder were introduced in the fluidized bed; as a consequence, the obtained coatings are thicker than that without zirconium additions. When Zr powders are added in the fluidized bed, the deposition atmosphere drastically changes, leading to increase the deposition rate. Thermodynamic calculations were carried out to simulate the modifications in the CVD atmosphere in the Al/Zr deposition system in comparison to the single aluminization. In order to optimize the conditions of the deposition, parameters such as temperature and concentration of zirconium introduced into the bed were evaluated and compared with the results obtained for the single aluminum deposition.

Abstract: Ferritic steels are usually used in boiler or supercritical steam turbines which operate at temperatures between 600-650°C under pressure. Protective coatings are often applied in order to increase their oxidation resistance and protect them against degradation. In this study new Al-Mn protective coatings were deposited by CVD-FBR on P92 ferritic steel. The initial process parameters were optimized by thermodynamic calculations using Thermo-Calc software. Then, those parameters were used in the experimental procedure to obtain Al-Mn coatings at low temperature and atmospheric pressure. Co-deposition was achieved at moderate temperatures in order to maintain the substrates` mechanical properties. The coatings` microstructure and phase constitution was characterized. Fe-Al intermetallic coatings containing Cr and Mn were obtained. The phase constitution is discussed with reference to the Fe-Al-Mn ternary phase diagram. The effect of diffusion heat treatment on the phase transformations as well as the steam oxidation resistance of these coatings at 650°C and 800°C was investigated.