(1) To examine the microstructure, hardness, and anodic polarization of UFG Fe-Cr alloys with different Cr content and the effect of annealing
Regardless of the Cr content, following eight passes, all specimens had a similar HAGB fraction, indicating a UFG microstructure.
Grain fragmentation also can be seen in the initial of UFG structure formation.
It is interesting to note that even though the Cr content is less than that required for stainless steel, UFG material with 8 and 10% Cr showed improved corrosion resistance due to the stability of the passivation layer in the 1000 mol x [m.sup.-3] NaCl solution.
To investigate the effect of the state of equilibrium of the grain boundaries on the corrosion resistance, heat treatment was applied to the UFG material.
Based on the GD-OES Cr profile shown in Figure 15, the passivation layer on UFG material is richer than that in Cr on CG material.
Due to such design of the tool and the use of optimal parameters, the VCH provides the formation of a ferritic class UFGS (Figures 2 and 3) with a grain size on the surface up to 190 nm, a high density of dislocations, and microstresses in the lattice (Figure 4).
The UFGS has an increased lattice parameter, which decreases depth (Figure 4).
The surface UFGS of the sample obtained under optimal conditions was investigated for wear resistance and corrosion-electrochemical characteristics.
The improvement in corrosion characteristics can also be attributed to the diffusion of chromium along the grain boundaries into the UFGS, leading to the formation of a chromium-rich passivation layer.
Thus, the conducted studies show that the VCH provides forming a gradient UFGS of a considerable depth and high microhardness on the steel surface.
(1) The results, presented in the article, prove that VCH makes it possible to obtain a gradient UFGS with high microhardness (up to 8.9 GPa) and hardening depth (up to 6 mm) due to increasing the tool mass.