Oxidation resistance of Mo(Si_1−xAl_x)₂ nanocrystalline films and characterization of their oxide scales by electrochemical impedance spectroscopy

Abstract

To explore the influence of Al alloying on the oxidation resistance of MoSi 2 , four Mo(Si 1Àx Al x ) 2 nanocrystalline films, with differing Al contents, were fabricated on Ti-6A1-4V substrates by a doublecathode glow discharge technique and their cyclic oxidation behavior was characterized at 500 C in air.The oxidation kinetics of the four Mo(Si 1Àx Al x ) 2 films was found to obey a subparabolic behavior with respect to the overall exposure, and their oxidation resistance was improved by Al additions. On the other hand, the electrochemical behavior of the oxide scales developed on the four Mo(Si 1Àx Al x ) 2 nanocrystalline films in a 3.5 wt% NaCl solution was studied using electrochemical-impedance spectroscopy (EIS). The impedance data showed that with increasing oxidation time, the oxide scales transformed from a homogeneous and dense structure to a duplex structure consisting of a porous outer layer and a denser inner layer. The resistance of the oxide scales increased with increasing Al addition, implying an enhanced protective ability of the oxide scales by Al alloying in media containing chlorine ions. The findings represent a step forward in improving the surface integrity of alloy components used in the hot zones of jet engines.

In vitro antibacterial properties of MoO3/SiO2/Ag2O nanocomposite coating prepared by double cathode glow discharge technique

“…Subsequently, the polished substrate specimen was ultrasonically cleaned in acetone, alcohol, and finally dried with cold air. The Ag-free MoO 3 -SiO 2 nanocomposite coating and Ag-containing MoO 3 -SiO 2 nanocomposite coating were deposited by a double cathode glow discharge system [21] employing two targets with stoichiometric ratios of Mo 50 Si 50 and Mo 47.5 Si 47.5 Ag 5 , respectively. In attempts to avoid the negative effect of residual gas on quality of coatings [22], before sputter deposition, the chamber was pumped down to a residual gas pressure of 5 × 10 −4 Pa. Substrate specimens were etched by Ar ion bombardment at a potential of −650 V for 20 min to get rid of any contamination from the specimen surface.…”