Multilayered Coatings for High-Temperature Steam Oxidation: TGA Studies up to 1000 °C

Abstract

The aim of the study was to obtain a preliminary data focused on the steam oxidation performance of multilayered coatings deposited on 310 stainless steel and 800H Incoloy. The coatings were obtained through the aluminizing thermal diffusion technology with the formation of aluminides; some coating options had an additional top layer of selected composition. In this study, five different coating systems, as well as uncoated metals, were exposed at 1000°C using thermogravimetric analysis instrumentation simulating an initial stage of steam oxidation corrosion. In this work, along with determination of the mass change of the samples, microanalyses using light optical microscopy, scanning electron microscopy (SEM) equipped with energy x-ray dispersive spectrometry (EDS), as well as surface micro-hardness determination, have been carried out. The designed coating systems demonstrated promising high-temperature steam oxidation performance with no breakaway degradation issues.

Sulfidation-Oxidation Resistance of Thermal Diffusion Multi-Layered Coatings on Steels

“…In our case, thermodynamically stable aluminide layers are covered with another thermodynamically stable Al 2 O 3 film well bonded to “original” aluminides. The absence of the spallation issue for this type of material corresponds well with other high-temperature oxidation studies [ 31 , 33 , 35 , 36 , 37 , 38 ].…”

“…As noted above, the exposure in the oxygen-rich gas, despite the presence of H 2 S, promoted surface oxidation of the aluminides with formation of a thin, up to ~2.5–4 µm, protective layer. Although the surface of samples A and 6A contains Fe, Cr, Ni, Al, and O ( Table 3 ), i.e., oxidized aluminides, it is suggested, according to published data [ 31 , 33 , 35 , 36 , 37 , 38 , 39 , 41 ], that the most external layer contains an extremely thin Al 2 O 3 film. This film is well-adhered to the Al-rich aluminides, especially in the case of smoother 6A samples.…”

“…The aluminized samples have three to four layers ( Figure 2 ), where each layer differentiates in Al contents and contains different aluminides according to the diffusion-induced process [ 28 , 35 , 36 , 37 , 39 ]. Thus, the transition layer (the first layer covering the steel substrate) mostly consists of the Me 3 Al (e.g., Fe 3 Al) phase, while the next (main) layer mostly consists of FeAl (for the carbon steel substrate) or Fe(Cr,Ni)Al (for the stainless steel substrate).…”

“…This peeling-off issue is related to the imperfectness of the TiO2 layer applied and that this layer became thicker than required; however, despite this issue, the nano-sized TiO2 particles easily penetrated the FeB surface asperities. The aluminized samples have three to four layers (Figure 2), where each layer differentiates in Al contents and contains different aluminides according to the diffusion-induced process [28,[35][36][37]39]. Thus, the transition layer (the first layer covering the steel substrate) mostly consists of the Me3Al (e.g., Fe3Al) phase, while the next (main) layer mostly consists of FeAl (for the carbon steel substrate) or Fe(Cr,Ni)Al (for the stainless steel substrate).…”

“…Some reliable coatings are inapplicable for protection of the inner surface of long tubing and complex shape components. In contrast, the thermal diffusion surface engineering technology, specifically boronizing and aluminizing of steels, can be used to protect critical components, including long tubing, exposed to harsh corrosion conditions [ 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ]. Recently, advanced coating materials obtained through the thermal diffusion process were considered and tested, for the first time, for high-temperature sulfidation applications with promising results after exposure in H 2 S-Ar flows at 500 °C [ 39 ].…”