NaF assisted preparation and the improved corrosion resistance of high content ZnO doped plasma electrolytic oxidation coating on AZ31B alloy

In the present research,the NaF assisted plasma electrolytic oxidation(PEO)is designed to fabricate the high-content ZnO nanoparti-cles doped coating on AZ31B alloy.The microstructure,phase constituents and corrosion behavior of the PEO coatings are investigated systematically.The results reveal that the introduction of NaF promotes the formation of MgF2 nanophases in the passivation layer on Mg alloy,decreasing the breakdown voltage and discharge voltage.As a result,the continuous arcing caused by high discharge voltage is alleviated.With the increasing of NaF content,the Zn content in the PEO coating is enhanced and the pore size in the coating is decreased correspondingly.Due to the high-content ZnO doping,the PEO coating protected AZ31B alloy demonstrates the better corrosion resistance.Compared with the bare AZ31B alloy,the high-content ZnO doped PEO coated sample shows an increased corrosion potential from-1.465 V to-1.008 V,a decreased corrosion current density from 3.043×10^(-5) A·cm^(-2) to 3.960×10^(-8) A·cm^(-2) and an increased charge transfer resistance from 1.213×10^(2) ohm·cm^(2) to 2.598×10^(5) ohm·cm^(2).Besides,the high-content ZnO doped PEO coated sample also has the excellent corrosion resistance in salt solution,exhibiting no obvious corrosion after more than 2000 h neutral salt spraying and 28 days’immersion testing.The improved corrosion resistance can be ascribed to the relative uniform distribution of ZnO in PEO coating which can transform to Zn(OH)2 and form a continuous protective layer along the corrosion interface.

Improvement of plasma uniformity and mechanical properties of Cr films deposited on the inner surface of a tube by an auxiliary anode near the tube tail

In order to improve the length of plasma in a whole tube and mechanical properties of Cr films deposited on the inner surface of the tube, a high-power impulse magnetron sputtering coating method with a planar cathode target and auxiliary anode was proposed. The auxiliary anode was placed near the tube tail to attract plasma into the inner part of the tube. Cr films were deposited on the inner wall of a 20# carbon steel tube with a diameter of 40 mm and length of 120 mm. The influence of auxiliary anode voltage on the discharge characteristics of the Cr target, and the structure and mechanical properties of Cr films deposited on the inner surface of the tube were explored. With higher auxiliary anode voltage, an increase in substrate current was observed, especially in the tube tail. The thickness uniformity, compactness, hardness and H/E ratios of the Cr films deposited on the inner surface of the tube increased with the increase in auxiliary anode voltage. The Cr films deposited with auxiliary anode voltage of 60 V exhibited the highest hardness of 9.6 GPa and the lowest friction coefficient of 0.68.

Tuning Superhydrophobic Materials with Negative Surface Energy Domains

Hydrophobic/superhydrophobic materials with intrinsic water repellence are highly desirable in engineering fields including antiicing in aerocrafts,antidrag and anticorrosion in ships,and antifog and self-cleaning in optical lenses,screen,mirrors,and windows.However,superhydrophobic material should have small surface energy(SE)and a micro/nanosurface structure which can reduce solid-liquid contact significantly.The low SE is generally found in organic materials with inferior mechanical properties that is undesirable in engineering.Intriguingly,previous theoretical calculations have predicted a negative SE forθ-alumina(θ-Al_(2)O_(3)),which inspires us to use it as a superhydrophobic material.Here,we report the experimental evidence of the small/negative SE ofθ-Al_(2)O_(3) and aθ-Al_(2)O_(3)-based superhydrophobic coating prepared by one-step scalable plasma arcing oxidation.The superhydrophobic coating has complete ceramic and desired micro/nanostructure and therefore exhibits excellent aging resistance,wear resistance,corrosion resistance,high-temperature tolerance,and burning resistance.Owing to the rarity of the small/negative SE in inorganic materials,the concept to reduce SE byθ-Al_(2)O_(3) may foster a blowout to develop robust superhydrophobicity by complete inorganic materials.