Microestrutura e resistência à corrosão do aço AISI 316L sinterizado, aditivado com boro, diboreto de titânio, titânio e nióbio

Abstract

AISI 316L stainless steel is widely used in biomedical applications due to its biocompatibility and corrosion resistance; however, it presents limitations when processed by conventional powder metallurgy, such as residual porosity and lower corrosion resistance in physiological environments. This work investigated the effect of adding boron (0.4% by mass) as a liquidphase sintering activator, combined with titanium (0.5%), niobium (1.0%), and titanium diboride (4.5%), on the microstructure and corrosion resistance of sintered 316L steel. The compositions were prepared by mixing powders, compacted at 700 MPa, and sintered at 1240 °C for 30 min in an argon atmosphere. The starting powders were characterized by X-ray diffraction, laser particle size analysis, and scanning electron microscopy. The sintered materials were evaluated for density, porosity, microstructure (optical microscopy and SEMEDS), and Vickers microhardness. Corrosion resistance was determined by open-circuit potential and potentiodynamic polarization measurements in simulated body fluid (SBF) solution at 37 °C. Boron addition reduced porosity from 4.6% to 3.1% and increased the microhardness of the austenitic matrix by 41% (from 215 to 303 HV). Chromium- and molybdenum-rich borides were identified at the grain boundaries of the boron-added compositions. All boron-containing compositions exhibited a higher open-circuit potential than pure 316L. The 316L-0.4B-4.5TiB2 composition exhibited the best electrochemical performance, with a polarization resistance 69 times higher and a corrosion current density 50 times lower than the reference composition. The 316L-0.4B-4.5TiB2 system, not yet explored in the literature for conventional powder metallurgy, presented the best combination of properties in a simulated physiological medium, indicating potential for biomedical applications. [resumo fornecido pelo autor]