Diangang Wang

In vitro degradation and electrochemical corrosion evaluations of microarc oxidized pure Mg, Mg-Ca and Mg-Ca-Zn alloys for biomedical applications.

Calcium phosphate (CaP) ceramic coatings were fabricated on pure magnesium (Mg) and self-designed Mg-0.6Ca, Mg-0.55Ca-1.74Zn alloys by microarc oxidation (MAO). The coating formation, growth and biomineralization mechanisms were discussed. The coating degradability and bioactivity were evaluated by immersion tests in trishydroxymethyl-aminomethane hydrochloric acid (Tris-HCl) buffer and simulated body fluid (SBF) solutions, respectively. The coatings and corrosion products were characterized by scanning electron microscope (SEM), X-ray diffractometer (XRD), X-ray photoelectron spectrometer (XPS) and fourier transform infrared spectrometer (FT-IR). The electrochemical workstation was used to investigate the electrochemical corrosion behaviors of substrates and coatings. Results showed that Mg-0.55Ca-1.74Zn alloy exhibits the highest mechanical strength and electrochemical corrosion resistance among the three alloys. The MAO-coated Mg-0.55Ca-1.74Zn alloy has the potential to be served as a biodegradable implant.

LASER SURFACE MODIFICATION OF TITANIUM ALLOYS—A REVIEW

Recent developments of laser surface modification of titanium alloys for increasing their corrosion, wear and oxidation resistance are introduced. The effects of laser processing parameters on the resulting surface properties of titanium alloys are reviewed. The problems to be solved and the prospects in the field of laser modification of Ti alloys are discussed. Due to the intrinsic properties, a laser beam can be focused onto the metallic surface to produce a broad range of treatments depending on the input energy. Thus, composite strengthening coatings can be fabricated by the methods of laser alloying, cladding, pulse laser deposition (PLD), etc., which are promising techniques of producing a layer of new materials on the surface of titanium alloys.

RECENT DEVELOPMENTS IN ZIRCONIA THERMAL BARRIER COATINGS

Thermal barrier coatings (TBC) are finding increasing applications in aeronautical, chemical, metallurgy industries, etc. As a ceramic material, ZrO2 is one of the most widely used for TBCs owing to its excellent shock resistance, low thermal conductivity and relatively high coefficient of thermal expansion (CTE). In this paper the thermomechanical properties of ZrO2 and the evolution of ZrO2-TBCs are reviewed. The failure mechanism of TBCs and corresponding methods for lengthening the lifetime of TBCs are discussed. The advantages and disadvantages of graded thermal barrier coatings (GTBC) as well as the problems to be solved in fabricating advanced TBCs are elucidated.

Dissolution and precipitation behaviors of silicon-containing ceramic coating on Mg-Zn-Ca alloy in simulated body fluid.

We prepared Si-containing and Si-free coatings on Mg-1.74Zn-0.55Ca alloy by micro-arc oxidation. The dissolution and precipitation behaviors of Si-containing coating in simulated body fluid (SBF) were discussed. Corrosion products were characterized by scanning electron microscope (SEM), X-ray diffractometer (XRD), fourier transform infrared spectrometer (FT-IR) and X-ray photoelectron spectrometer (XPS). Electrochemical workstation, inductively coupled plasma atomic emission spectrometer (ICP-AES), flame atomic absorption spectrophotometer (AAS) and pH meter were employed to detect variations of electrochemical parameter and ions concentration respectively. Results indicate that the fast formation of calcium phosphates is closely related to the SiOx(n-) groups, which induce the heterogeneous nucleation of amorphous hydroxyapatite (HA) by sorption of calcium and phosphate ions.

RESEARCH STATUS ABOUT SURFACE MODIFICATION OF BIOMEDICAL Ti AND ITS ALLOYS BY MICRO-ARC OXIDATION

Ti and its alloys are considered to be very promising in biological material field. But their biological activity and corrosion resistance in body fluid still need to be improved. As a novel technique for surface treatment, Micro-arc oxidation (MAO) is attracting interest from those who want to improve their implant properties through surface modification. This paper reviewed the application of MAO on biomedical Ti-alloys. The structure characteristic such as surface and cross-section micrographs, phase components, and element distribution were analyzed. The mechanical and biological properties of MAO films were further discussed on this basis. The effects of current density, voltage, and electrolyte on the structure and properties of the films were summarized.

The Current Techniques For Preparing Bioglass Coatings

Bioglasses are promising alternatives as biomedical materials to repair or replace damaged parts of bones because of its good bioactivity and biocompatibility. It is possible to combine the bone-bonding ability of the bioglass surface with the high mechanical properties of the metallic substrate though the coating of metallic implants with bioglass. The principles and characteristics of some coating techniques, including sintering, plasma spray, sol-gel, electrophoresis deposition, ion beam assisted deposition and pulsed laser deposition, are introduced. Their current applications in preparing bioglass coatings are reviewed in detail. The future application trends are also reviewed.

Microstructure And Element Distributions Of Ceramic-Like Coatings On The Az91 Alloy By Micro-Arc Oxidation

Ceramic-like coatings were deposited on the substrate of the AZ91 alloy by micro-arc oxidation (MAO). Many methods like X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron diffraction spectroscopy (EDS) were used to analyze the structure and composition of the coating. XRD showed that the MAO coating was mainly composed of MgO. The results of SEM showed that the coating surface possessed a porous microstructure and the pore size was in the range of 1–3 μm. EDS indicated that the coating matrix was relatively dense and had a homogeneous thickness. The element silicon from the applied electrolyte could be absorbed into the coating in the MAO process. The hardness of the MgO coatings could reach 513 HV0.025 that was about four times higher than that of the substrate. It is expected that the coatings have a great potential in the surface protection of magnesium alloys.

The Application Of Pulsed Laser Deposition In Producing Bioactive Ceramic Films

Pulsed laser deposition (PLD) is a relatively new technique for producing thin films. It presents unique advantages for the deposition of bioactive ceramics. The mechanism and characteristics of the technique PLD are introduced. Its applications and current research status in hydroxyapatite and bioglass thin films are reviewed. The effect of processing parameters of PLD, including atmosphere, substrate temperature, laser wavelength and target properties, on the structures and the properties of the hydroxyapatite film, is analyzed in detail. Future application trends are also analyzed.

MICROSTRUCTURES AND WEAR PROPERTIES OF THE COMPOSITE COATINGS LASER-FABRICATED ON TITANIUM ALLOY Ti-6Al-4V

Composite coatings containing titanium carbides and borides are produced on the surface of Ti-6Al-4V alloy by laser alloying technique. Microstructural analysis shows that coarse bulk-like and dendritic compounds are formed when alloyed with boron and carbon, separately. However, fine and uniformly distributed dendritic compounds are produced when alloyed with boron and carbon mixed powders. With microhardness of 1450–1600 HV0.1, the coatings have excellent wear resistance compared with as-received sample.

Effect of Na2WO4 on Growth Process and Corrosion Resistance of Micro-arc Oxidation Coatings on 2A12 Aluminum Alloys in CH3COONa Electrolyte

Ceramic coatings were deposited on 2A12 aluminum alloys using micro-arc oxidation (MAO) technology in CH3COONa-Na2WO4 electrolyte. The MAO process was studied by recording the current-time curve. The influences of Na2WO4 concentrations on the coatings in CH3COONa electrolyte were investigated. The results show that the Na2WO4 concentrations affect the MAO process and performances of the coatings directly. Na2WO4 in excess is harmful for the formation of Al2O3 in this electrolyte. The corrosion resistance was enhanced with the decrease of Na2WO4 concentration.