Ricky Fu

As implanted bone fixation materials, magnesium (Mg) alloys have significant advantages because the density and elastic modulus are closest to those of the human bone and they can bio-degrade in the physiological environment. However, Mg alloys degrade too rapidly and uncontrollably thus hampering clinical adoption. In this study, a highly corrosion-resistant zinc-phosphate-doped micro-arc oxidation (MAO) coating is prepared on the AZ31B alloy, and the degradation process is assessed in vitro. With increasing zinc phosphate concentrations, both the corrosion potentials and charge transfer resistance of the AZ31B alloy coated with MAO coatings increase gradually, while the corrosion current densities diminish gradually. Immersion tests in the simulated body fluid (SBF) reveal that the increased zinc phosphate concentration in MAO coating decreases the degradation rate, consequently reducing the …

In the present research, the NaF assisted plasma electrolytic oxidation (PEO) is designed to fabricate the high-content ZnO nanoparticles 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 …

In the present study, a three-dimensional multi-interface structured zinc phosphate particle with large specific surface area was prepared by regulating the zinc phosphate crystal growth process, which was applied to develop a waterborne epoxy resin coating with better corrosion resistance. The results reveal that the multi-interface structured zinc phosphate particles could well coalesce with epoxy resin. Compared with the waterborne coating doped with and without two-dimensional zinc phosphate sheets, the multi-interface structured zinc phosphate particles doped waterborne epoxy resin coating has highest corrosion potential, lowest corrosion current density and the highest low-frequency impedance, which indicates the obvious benefits of multi-interface structured zinc phosphate particles on corrosion resistance. Moreover, the electrochemical properties tests on the waterborne epoxy resin coatings immersed …

Corrosion protection of magnesium alloys is a challenge in industrial applications because of the high chemical reactivity of Mg. In this work, a coating is prepared by plasma electrolytic oxidation (PEO) on the AZ31B Mg alloy and then modified by insoluble zinc phosphate to improve the corrosion resistance. To avoid the influence of the weak acidic Zn-containing electrolyte on the formation of the passivation layer on the magnesium alloy, a two-step process is designed to first produce a passivation layer before introduction of zinc phosphate. Zinc phosphate is mainly distributed on the surface and the sidewalls of the holes in the porous coating and blocks the interactions between the corrosive solution and Mg substrate. The corrosion potential of the optimal coating (Zn-15) increase while the passive current density at the terminal potential decreases, suggesting the significantly improved corrosion resistance …

Coherent grain boundaries (CGBs) has been revealed to improve the hardness and toughness simultaneously, but the density are not enough to increase their mechanical properties. Herein, hetero-interfaces are formed by introducing ion bombardment during magnetron sputtering to increase the amount of CGBs in the CrN coatings. By optimizing the sub-layer thickness, the quantity and width of CGBs from the (111) to (200) orientations increase significantly and consequently, the hardness and toughness of the CrN coating increase to 33.4 GPa and 14.98 MPa m1/2, respectively. At last, the effect of the different CGBs to the coating strengthen is discussed.

Etching of the cathodes in magnetron sputtering determines the plasma discharge properties and deposition efficiency. In high-power and high-ionization discharges, etching becomes more complicated, resulting in inaccurate results if the conventional models are still used. This work aims at establishing an accurate dynamic model for high-power and high-ionization discharges by combining the cellular automata (CA) method and particle-in-cell/Monte Carlo collision (PIC/MCC) method, in which all the interactions pertaining to the etching morphology, plasma density, electric field, and magnetic field are considered. In high-power discharges such as continuous high-power magnetron sputtering (C-HPMS), strong self-sputtering and intense gas rarefaction stemming from the high temperature in the vicinity of the target influence the etching behavior. Compared to the experimental results, the morphology simulated …

Although aluminum alloys are widely used in the aerospace and automotive industry, they are susceptible to local corrosion and wear during long-term service in harsh environment. In this work, micro-arc oxidation (MAO) coatings containing quasi-2D sericite microplates are prepared on the 2024 aluminum alloy, and their corrosion and wear resistance are investigated. The results reveal that the sericite-incorporated MAO sample prepared in the 15 g/L sericite electrolyte (M−15) possesses the best corrosion resistance in 3.5 wt% NaCl solution, as manifested by a corrosion current density of 2.93 × 10−10 A ∗ cm−2 that is 4 orders of magnitude less than that of the 2024 Al alloy substrate. The wear resistance of MAO coating is also improved by the addition of sericite microplates, which is shown by the low wear rate and reduced coefficient of friction (∼0.3) of M−15 against steel ball. Our mechanistic study reveals …

Hydrogen embrittlement has become a hot research topic due to the rapid development of hydrogen energy and coating technology is regarded as the most efficient method to mitigate hydrogen embrittlement. However, the grain gaps in coatings frequently serve as paths for hydrogen permeation thus decreasing the protecting effects. In this work, ion bombardment is performed during magnetron sputtering deposition of dense CrN coatings to decrease the formation of grain gaps. The compactness of the CrN coatings is improved by disrupting the growth of grains using energetic ion bombardment. Hydrogen permeation tests reveal that the apparent hydrogen diffusion coefficient and hydrogen permeability of the dense CrN coating 52.6 and 24.1 times less than those of the unprotected substrate. The tensile test also reveals excellent hydrogen embrittlement resistance compared to the X70 substrate and …