Papers by Author: Ying Li

Abstract: The isothermal and cyclic oxidation behaviors of a Ni-based superalloy with singlecrystalline (SC), polycrystalline and nanocrystalline (NC) structures were studied at 1000°C. Results indicated that a uniform oxides scale consisted of external Cr2O3 with little TiO2 and internal continuous Al2O3 formed on SC alloy. A non-uniform external oxide of which some locations were nodule-like scale was formed on surface of cast alloy. The nodule-like parts consisted of TiO2, Cr2O3 and serious internal oxidation of Al, and rest flat surface was a Cr2O3 and Al2O3 layer. A continuous Al2O3 layer formed on the sputtered NC coating. The micro-structure influenced the oxidation mechanism and resulted in different oxide scale formed on three materials, which greatly influenced materials’ oxidation and cyclic-oxidation resistance.

Abstract: The corrosion behavior of a nanocrystalline (NC) low carbon steel (LCS) surface film deposited on a conventional polycrystalline (PC) LCS by magnetron sputtering was studied in 0.5 M H2SO4 solution using impedance and potentiodynamic polarization techniques. The corrosion inhibiting effect of a non toxic organic compound (methionine) and synergistic KI additives was also studied. Microstructure characterization by X-ray diffraction and atomic force microscopy revealed no phase changes due to nanoprocessing and the grain size of the NC surface layer was ~ 40 nm. Electrochemical results show that both the PC and NC surfaces underwent active corrosion with no transition to passivation in the potential range studied. Surface nanocrystallization however increased the corrosion susceptibility of low carbon steel more than two-fold, leading to a decrease in interfacial impedance and an increase in the kinetics of the anodic reaction. Methionine inhibited the corrosion of both specimens with comparable inhibition efficiencies. Iodide ions synergistically increased the inhibition efficiency of methionine on both specimens. This synergistic effect was more pronounced for the bulk steel and has been discussed vis-à-vis the more positive surface charge on bulk steel surface at the corrosion potential compared to the nanocrystalline surface.