Abstract
The oxidation behavior of four valve steels (X33CrNiMn23-8, X50CrMnNiNbN21-9, X53CrMnNiN20-8 and X55CrMnNiN20-8) covered with thin sputter-deposited coatings containing chromium and nickel was studied under isothermal and thermal shock conditions. It was determined that coated steels exhibit greater resistance against oxidation than steels with unmodified surfaces. This effect results from the formation of chromium-rich oxides (e.g., Cr2O3, NiCr2O4, MnCr2O4) during oxidation of the surface modified steel. These oxides exhibited better protective properties than the products grown on unmodified steels (namely Fe3O4 and Fe2O3). The entirety of the obtained experimental results confirms the possibility of increasing the scaling resistance of valve steels by using around 1-µm-thick chromium-rich protective Cr–Ni coatings.
Highlights
One of the most effective methods for protecting materials that work at high temperatures and in aggressive gas atmospheres is the application of protective coatings [1,2,3,4]
This research showed that such a thin chromium layer facilitates the growth of a scale consisting of chromiumrich oxides (Cr2O3, CrMn2O4, Cr1.5Mn1.5O4) that demonstrate very good protective properties and enhance the heat resistance of the protected steel
The effect that the aforementioned coating has on the corrosion resistance of the steel can be explained as the thin chromium layer initiating the formation of the above-mentioned oxides, after which the coating quickly disappears and the scale continues to grow due to outward chromium diffusion from the metallic substrate
Summary
One of the most effective methods for protecting materials that work at high temperatures and in aggressive gas atmospheres is the application of protective coatings [1,2,3,4]. Among the most effective are so-called thermal barrier coatings (TBC), which combine excellent protective properties against both high temperatures and aggressive oxidizing gases [5,6,7,8,9,10,11,12]. These coatings are relatively thick (generally 100 μm–2 mm), which makes it impossible to deposit them on wellmatched machine parts, because such thick coatings would become damaged during operation. As a result, coated valve steels exhibit higher oxidation resistance under isothermal conditions compared to respective unmodified steels for a significantly longer time than the lifespan of the deposited coatings
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