Revealing the Enhanced Passivation and Anti-Corrosion Performance of Surface-Nanocrystallization-Modified Cr-Alloyed Rebar via Electrochemical Testing and XPS Depth Analysis

Surface nanocrystallization (SNC) modification can be used to realize the high-efficiency derusting of rusted Cr-alloyed rebar and obtain nanostructured grains on the surface of the rebar. The corrosion resistance performance of SNC rebar in a simulated Cl--containing concrete pore solution was evaluated on the basis of electrochemical experiments. Potentiodynamic polarization testing showed that the passivation current density of the SNC rebar was about 18% of that of the rusted rebar. The structural composition of the passivation film of the SNC rebar in a concrete environment was studied using a novel characterization method, namely XPS deep sputtering, which confirmed that it had higher concentrations of Cr/Fe oxide and hydroxide, and therefore exhibited an enhanced degree of oxidation. Moreover, scanning electron microscopy and transmission electron microscopy were employed to investigate the microstructural characteristics of the SNC rebar, which was characterized by nanostructured grains with grain sizes ranging from 250 nm to 300 nm and which contained massive high-energy crystal defects, thereby promoting the film-forming reaction of Cr/Fe elements. The results of XPS depth analysis and microstructure characterization demonstrated that the SNC rebar exhibited excellent passivation performance in the concrete environment. These findings offer a new perspective on enhancing the passivation performance and chloride resistance of alloyed rebar, and provide guidance on the implementation of SNC rebar in actual engineering applications.