Barreiras à base de ligas de alumínio para a difusão do hidrogênio nos substratos ferrosos

Abstract

The hydrogen barrier performance of aluminium-based coatings (Fe-Al, Al-Zr) deposited on ferritic substrates by high velocity oxy-fuel and magnetron sputtering was studied. Hydrogen interaction at the chemical stability and morphological properties of the aluminium-alloy/ferrous substrate composites system were characterized through electrochemical hydrogen permeation tests at room temperature. The morphology, composition and structure were studied by scanning electron microscopy (SEM) and Xray diffraction (XRD) analysis. For the FeAl coated samples by thermal spray process, the lowest hydrogen diffusivity was obtained for the No 2 coating, 24 times lower than the uncoated substrate. It was verified that the apparent hydrogen solubility through Fe-Al coating increases considerably by surface defects characteristic of thermal spraying coatings that acts as hydrogen traps, thus protecting the material against embrittlement by hydrogen. It has been found that the Al-Zr coating becomes partially amorphous with higher Zr content. The Al–Zr (9 %at. Zr) coating has a structure composed of a homogenous metastable, supersaturated solid solution α-Al (fcc) and an amorphous phase. Electrochemical hydrogen permeation measurements showed that hydrogen diffusivity decreases when the amount of zirconium increases. The lowest apparent hydrogen diffusivity was obtained for the Al–Zr coating with 9 at% Zr and was equal to 1,5 × 10-12 m2 .s-1