Ruisong Yang

Structure and corrosion resistance of modified micro-arc oxidation coating on AZ31B magnesium alloy

Abstract A hydrophobic surface was fabricated on a micro-arc oxidation (MAO) treated AZ31 Mg alloys via surface modification with myristic acid. The effects of modification time on the wettability of the coatings were investigated using the contact angle measuring device. The surface morphologies and structure of the coatings were evaluated using SEM, XRD and FT-IR. The corrosion resistance was investigated by potentiodynamic polarization curves and long-term immersion test. The results showed that the water contact angle (CA) increases gradually with modification time from 0 to 5 h, the highest CA reaches 138° after being modified for 5 h, and the number and size of the micro pores are decreased. The modification method hardly alters crystalline structure of the MAO coating, but improves the corrosion resistance based on the much positive potential and low current density. Moreover, the corrosion resistance and hydrophobicity can be enhanced with increasing the alkyl chain. The wetting and spreading for the alkylcarboxylate with low surface energy become easier on the micro-porous surface, and alkylcarboxylate monolayer will be formed through bidentate bonding, which changes the surface micropores to a sealing or semi-sealing structure and makes the MAO coating dense and hydrophobic. All the results demonstrate that the modification process improves the corrosion protection ability of the MAO coating on AZ31B Mg alloy.

In vitro studying corrosion behavior of porous titanium coating in dynamic electrolyte

Porous titanium (PT) is considered as a promising biomaterials for orthopedic implants. Besides biocompatibility and mechanical properties, corrosion resistance in physiological environment is the other important factor affecting the long stability of an implant. In order to investigate the corrosion behavior of porous titanium implants in a dynamic physiological environment, a dynamic circle system was designed in this study. Then a titanium-based implant with PT coating was fabricated by plasma spraying. The corrosion resistance of PT samples in flowing 0.9% NaCl solution was evaluated by electrochemical measurements. Commercial pure solid titanium (ST) disc was used as a control. The studies of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) show that the pores in the PT play a negetive part in corrosion resistance and the flowing electrolyte can increase the corrosive rate of all titanium samples. The results suggest that pore design of titanium implants should pay attention to the effect of dynamic process of a physiological environment on the corrosion behavior of implants.

The synthesis of TiC/TiNi powders and bulk materials

Abstract The titanium, nickel and carbon powders were ball milled and reacted in molten NaCl and KCl mixed salts. After reacted in molten salts, titanium carbide and titanium nickel composite powders were synthesised. Titanium carbide particles tend to inhibit the formation of the rhombohedral phase. Then the titanium carbide and titanium nickel composite powders were put into graphite die to produce bulk materials by hot pressing. After hot pressing, it could be seen that the titanium carbide particles dispersed in the TiNi and Ti2Ni matrix.

Interface stability and microstructure of ultrathin Mo/MoN diffusion barrier in Cu interconnects

Abstract An ultrathin Mo (7 nm)/MoN (3 nm) bilayer film covered by Cu film was deposited on the Si substrate using reactive magnetron sputtering in N2/Ar ambient. The film stacks of Cu/Mo (7 nm)/MoN (3 nm)/Si were then annealed in a vacuum chamber at 500–800°C for 1 h. X-ray diffraction, scanning electron microscopy, cross-sectional transmission electron microscopy and energy dispersive X-ray spectroscopy line scans were employed to investigate the microstructure evolution and the diffusion behaviour of the film stacks. The results show that the Mo (7 nm)/MoN (3 nm) bilayer film as a diffusion barrier has sufficient interface stability, which can prevent Cu atom diffusion at elevated temperatures up to 700°C. The relationship between the interface stability and the microstructure of the bilayer barrier is characterised in detail.