Ref.: MmeCo28-002
Apresentador: Edson Daniel Banak Varela
Autores (Instituição): Varela, E.D.(Universidade Federal do Paraná); d'Oliveira, A.C.(Universidade Federal do Paraná);
Resumo:
This study investigated the impact of powder-pack aluminizing surface treatment on the high-temperature oxidation of AISI316L stainless steel components fabricated using different additive manufacturing techniques: PTA-DED, L-DED, and L-PBF, during isothermal oxidation at 1000°C. The surface treatment was also conducted in a rolled AISI316L for comparison. Aluminization was performed at 850°C for 6 hours with a powder-pack mixture of 10% Al, 5% NH4Cl, and 85% Al2O3. Coatings were characterized using scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), and X-ray diffraction (XRD). Regardless of the substrate used, aluminized coatings consisted of an external layer with high concentrations of aluminum intermetallic phases (FeAl3 and Fe2Al5) and an interdiffusion zone containing intermetallic phases with lower aluminum concentrations (FeAl and ?-Fe(Al)). The microstructure of the substrates influenced the coating thickness, the PTA-DED coarsert structure resulting in a thinner external layer and a thicker interdiffusion zone compared to other substrates. Despite different microstructures, L-DED and L-PBF substrates exhibited similar aluminized coatings, as did the rolled aluminized material. This indicates that interdiffusion reactions at the coating/substrate interface significantly affect coating formation kinetics. Oxidation tests showed that aluminide coatings remained stable above 1000°C by promoting preferential alumina (Al2O3) growth, thereby enhancing oxidation resistance. However, for aluminum diffusion coatings, metallurgical stability at high temperatures is crucial. Excessive aluminum diffusion into the substrate can render the coating ineffective in protecting the substrate due to a lack of oxide-forming elements and can also compromising the mechanical properties of the substrate. At elevated temperatures, Al atoms from intermetallic phases with higher aluminum concentrations (FeAl3 and Fe2Al5) diffuse towards the substrate, enlarging the interdiffusion zone and reducing the external layer until the coating is primarily composed of FeAl and ?-Fe(Al). The growth of the interdiffusion layer during high-temperature exposure is also influenced by the substrate structure, with the coarser PTA-DED structures resulting in a thicker layer than substrates with finer structures. Therefore, tailoring powder-pack aluminization parameters is crucial to protect additive materials in industrial applications requiring oxidation-resistant stainless steel with surface aluminizing.