Abstract: Aluminizing is applied in stainless steels whenever oxidation or carburization resistance is an important issue that might compromise performance of parts and equipment. In this process Al is deposited in the surface of the metal and diffuses to react and form continuous layers of aluminide phases. Those layers act as reservoir of Al for the formation of protective and slow growing Al-based oxide scale. According to the recent work of Majumdar in 2017  during pack aluminization of austenitic stainless steels at temperature above 700°C, multiple iron aluminides layers consisting of Fe2Al5/FeAl/Fe(Al) are formed from the surface to the substrate, respectively. The author also identified that the controlled oxidation of the aluminide layers forms an α-Al2O3 scale, the most stable allotropic phase of the Al-based oxides. Many studies have addressed the features of the treated surface. Nevertheless, whenever a new material is being design that might interfere with the diffusion mechanisms, new data is required to better understand and optimize the use of the protected part. Mohammadi in 2016, studied the oxidation resistance of the overaluminized HVOF coating . It was reported that the Al reservoir on the sprayed surface could sustain the growth and rehealing of the alumina scale.
This research contributes to this discussion as it investigates the impact of AISI 309 and 316 thermally sprayed coatings features on aluminizing surfaces. Particularly, the study analyzed how different content of oxides and porosity of the lamellae structure affect the formation and the quality of the Al coating.
Authors: Edson D.B. Varela and Ana Sofia C.M. D’Oliveira
Keywords: Pack aluminizing, Thermal spray coatings, Stainless steel