Effects of post-annealing treatment on the tribological and electrochemical properties of (Ti,Al,Cr,Si,Zr)N coated steels

Abstract

A non-equimolar compositionally complex nitride coating of (Ti,Al,Cr,Si,Zr)N was deposited on 304 stainless steel using arc evaporation of Ti80Si20, Al70Cr30, and Zr cathodes. Both the as-deposited and annealed coatings exhibit a face centered cubic nanocrystalline structure, as confirmed by detailed structural analyses. Annealing at 800 °C in ambient atmosphere caused the formation of a dense oxide layer containing SiO2 and TiO2 leading to a decrease in hardness H from 22.0 ± 5.9 to 16.9 ± 2.7 GPa and reduced modulus E from 232 ± 37 to 207 ± 21 GPa. Although this results in lower H/E and H3/E2 ratios, the annealed sample allows for a 31 % lower wear rate (7.50 × 10⁻¹³ m3/Nm). In 3.5 wt% NaCl solution, the annealed specimen showed a significant improved corrosion resistance with an Icorr value of 1.96 × 10⁻⁹ A·cm⁻², being 11.2 times lower than that of the as-deposited sample. Conversely, in 0.1 M H₂SO₄, the as-deposited coating exhibits a fourfold lower Icorr (3.30 × 10⁻⁸ A·cm⁻²) compared to the annealed one. The corrosion performance of these coatings is governed by the formation and stability of protective oxide layers, their wetting behavior, and the presence of microstructural defects—such as pin-holes or fast diffusion pathways—which, if not minimized or sufficiently dense, can facilitate the transport of corrosive species to the less corrosion-resistant substrate and accelerate degradation.