Improvement in Resistance to Steam Oxidation of Aluminide-Coated AISI 304 and AISI 316 Steel Produced by Chemical Vapor Deposition in a Fluidized Bed Reactor

Abstract

Various techniques have been used to deposit aluminium on ferritic and austenitic steels to increase their oxidation resistance. An aluminide coating was deposited on AISI 304 and AISI 316 stainless steels by chemical vapor deposition at 580°C for 1.5 h in a fluidized bed reactor. The as-deposited samples were treated at 750°C in Ar atmosphere for 2 h. Scanning electron microscopy/energy-dispersive X-ray spectroscopy and X-ray diffractometry were used to study morphology and composition. Deposition results indicated that FeAl, Fe 2 Al 5 , Al 0.99 Fe 0.99 Ni 0.02 , AlNi, and Fe 2 AlCr had formed. Specimens were oxidized in a steam loop at 750°C for 1000 h to evaluate the steam oxidation resistance of the coating. The thermodynamic software package Thermo-Calc was used for simulations under similar experimental oxidation conditions. Gravimetric measurements verified that the mass change of the coated samples decreased up to 100 times with respect to uncoated steels.

High performance of Al‐Si‐CVD‐FBR coating on P92 steel against steam oxidation at 650 °C: Part 1

“…As we know, the aluminides exhibit high stability in the presence of steam; they are good because they act as thermal barriers to hinder ionic mobility and they increase the potential energy barrier for diffusion. In addition, a film thickens as a consequence of its resistivity . Thus, the resistance of iron aluminides to chemical degradation in a number of high‐temperature environments correlates with the ability of these alloys to quickly form and maintain the protective Al 2 O 3 layer.…”

“…Aluminum‐silicon coating was deposited using the CVD‐FBR system at 580 °C for 2 h. CVD‐FBR characteristics for this research have been reported in previous works . The bed was a mixture of 100 wt% (Al + Si + Al 2 O 3 ) powder (99.9% pure, particle size under 400 μm diameter).…”

“…Some considerations and procedures were reported in a previous work . The results were compared with the literature and MS databases …”

“…Aluminum-silicon coating was deposited using the CVD-FBR system at 580°C for 2 h. CVD-FBR characteristics for this research have been reported in previous works. [17,18] The bed was a mixture of 100 wt% (Al + Si + Al 2 O 3 ) powder (99.9% pure, particle size under 400 μm diameter). Argon gas (99.999% purity) was used to fluidize the powder mixture, and hydrogen (H 2 ) and hydrogen chloride (HCl) were used as activators to generate an aluminum precursor.…”

“…Chemical vapor deposition (CVD) is a technique involving a reaction of gas mixtures at a predetermined temperature inside a vacuum chamber or reactor that contains substrates . CVD in a fluidized bed reactor (CVD‐FBR) is an improved CVD model that combines the advantages of thermal activation by heating and the advantages of fluidized beds, such as high mass and heat transfer inside the gases, which allows for a more uniform temperature and better mixture of reactive gases with fluidized particles . For this reason, it is an important alternative for depositing Al‐Si coatings on ferritic‐martensitic steels.…”