Sibo Shen

Influence of heat treatment on bond strength and corrosion resistance of sol-gel derived bioglass-ceramic coatings on magnesium alloy.

In this study, bioglass-ceramic coatings were prepared on magnesium alloy substrates through sol-gel dip-coating route followed by heat treatment at the temperature range of 350-500°C. Structure evolution, bond strength and corrosion resistance of samples were studied. It was shown that increasing heat treatment temperature resulted in denser coating structure as well as increased interfacial residual stress. A failure mode transition from cohesive to adhesive combined with a maximum on the measured bond strength together suggested that heat treatment enhanced the cohesion strength of coating on the one hand, while deteriorated the adhesion strength of coating/substrate on the other, thus leading to the highest bond strength of 27.0MPa for the sample heat-treated at 450°C. This sample also exhibited the best corrosion resistance. Electrochemical tests revealed that relative dense coating matrix and good interfacial adhesion can effectively retard the penetration of simulated body fluid through the coating, thus providing excellent protection for the underlying magnesium alloy.

Synthesis and characterization of a phytic acid/mesoporous 45S5 bioglass composite coating on a magnesium alloy and degradation behavior

In order to decrease the degradation rate and improve the bioactivity of a magnesium alloy, a phytic acid and mesoporous 45S5 bioglass composite coating (PMBC) has been synthesized on the AZ31 magnesium alloy by a two-step method. The phase, surface morphology and structure of the composite coatings were characterized by X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. The composite coating consisting of an interior layer of mesoporous 45S5 bioglass and an outer layer of phytic acid/magnesium phytic acid was dense, crack-free and had no remarkable interface between the inner and outer coating. The bonding strength of the composite coating to the magnesium alloy substrate was 15.2 ± 1.5 MPa. The immersion test in simulated body fluid (SBF) showed that the composite coating could provide obvious protection for the substrate and greatly decreased the degradation rate to 0.62 mg per cm2 per day from the uncoated sample of 2.93 mg per cm2 per day on the sixteenth day. And the outer coating of phytic acid could induce the formation of apatite, suggesting good bioactivity of the coated magnesium alloy.

Corrosion behavior of mesoporous bioglass-ceramic coated magnesium alloy under applied forces.

In order to research the corrosion behavior of bioglass-ceramic coated magnesium alloys under applied forces, mesoporous 45S5 bioactive glass-ceramic (45S5 MBGC) coatings were successfully prepared on AZ31 substrates using a sol-gel dip-coating technique followed by a heat treatment at the temperature of 400°C. In this work, corrosion behavior of the coated samples under applied forces was characterized by electrochemical tests and immersion tests in simulated body fluid. Results showed that the glass-ceramic coatings lost the protective effects to the magnesium substrate in a short time when the applied compressive stress was greater than 25MPa, and no crystallized apatite was formed on the surface due to the high Mg(2+) releasing and the peeling off of the coatings. Whereas, under low applied forces, apatite deposition and crystallization on the coating surface repaired cracks to some extent, thus improving the corrosion resistance of the coated magnesium during the long-term immersion period.