Investigation of Atmospheric Pressure CVD‐Produced Aluminum Coatings for the Protection of Steel from Corrosion

Abstract

AbstractThis study investigates the use of atmospheric pressure (AP)CVD‐produced aluminum (Al) coatings for the protection of steel from corrosion. Coatings produced through thermal decomposition of a triisobutylaluminum (TIBAL)‐based precursor at 548 and 573 K are shown to exhibit growth rates of 0.5 and 1.1 µm min−1, respectively. Glow discharge optical emission spectroscopy (GDOES) reveals that, in the main, the coatings consist of pure Al with oxygen present as a minor constituent. Results of the structural, morphological, electrical, and mechanical characterization reveal that the APCVD Al coatings exhibit a face center cubic (fcc) structure with no preferred orientation, a non‐columnar grain structure with grain size ranging from 3 to 10 µm, and a surface roughness close to 2 µm. Such coatings are also shown to offer an electrical resistivity of 3.5 µΩ·cm, a density of 2.60 g cm−3, and an adhesive strength of 703 kg cm−2. Cross‐sectional examination of coated samples indicate that the APCVD process can yield excellent step coverage and throwing power. Hydrogen embrittlement (HE) tests reveal that Al‐coated bars with no post baking experience premature failure due to the presence of incorporated reaction product, hydrogen, in the steel substrate. Samples post‐baked at 463 K for 23 h to remove the hydrogen from the substrate are shown to withstand the load for as long as 202 h. Corrosion studies conducted using potentiodynamic polarization measurements, electrochemical impedance spectroscopy, and salt fog tests show that the corrosion resistance of the APCVD Al coatings is comparable to that of pure Al foils, and that such coatings provide acceptable sacrificial protection for steel substrates.