Chuanzhong Chen

Microstructure and biological properties of micro-arc oxidation coatings on ZK60 magnesium alloy.

Ceramic coatings were prepared on ZK60 magnesium alloy in electrolyte with different concentration ratio of calcium and phosphorus (Ca/P) by micro-arc oxidation (MAO) technique at constant voltage. The microstructure, phase composition, elemental distribution, corrosion resistance, and adhesion of the coatings were investigated by scanning electron microscope (SEM), X-ray diffractometer (XRD), energy-dispersive X-ray spectrometry (EDS), electrochemical workstation, and scratch spectrometer, respectively. The coating biocompatibility was evaluated by in vitro cytotoxicity tests and systemic toxicity tests, and the bioactivity and degradability were evaluated by simulation body fluid (SBF) immersion tests. SEM shows that pores with different shapes distribute all over the coating surface. The adhesion and thickness of the coatings increases with increasing Ca/P ratio of electrolyte. The in vitro cytotoxicity tests and systemic toxicity texts demonstrate that the coatings have no toxicity to cell and living animal, which show that the coatings have excellent biocompatibility. XRD analysis shows that bioactive calciumphosphate (CaP) phases such as hydroxyapatite (HA, Ca(10)(PO(4))(6)(OH)(2)) and calcium pyrophosphate (CPP, Ca(2)P(2)O(7)) are induced in the immersed coatings, indicating that the MAO coatings have excellent bioactivity.

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.

Improvement in surface performance of Al3Ti+TiB2/(Ni coated WC) laser cladded coating with Al2O3/nano-Y2O3

Abstract Al3Ti+TiB2/(Ni coated WC) laser cladded coating on the Ti–6Al–4V alloy can increase microhardness and wear resistance of the substrate. Nevertheless, due to the actions of a large amount of M6C (Ni2W4C) and the coarse structure, the microhardness of this coating was only 2–3 times higher compared with the substrate. In this study, the Al3Ti+TiB2/(Ni coated WC)+Al2O3/nano-Y2O3 laser cladded coating has been researched by means of X-ray diffraction, scanning electron microscope and energy dispersive spectrometer. The experimental results indicated that with addition of the proper content of Al2O3/nano-Y2O3, the SiO2–Al2O3–Y2O3 system and the Al–Ni–Y amorphous alloy were produced, which were beneficial to increased microhardness and wear resistance of this coating. Furthermore, Al2O3/nano-Y2O3 can also decrease the M6C content, and refine the microstructure of this coating. Accordingly, the microhardness and wear resistance of the Al3Ti+TiB2/(Ni-coated WC) laser cladded coating have been greatly improved.

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.

DEVELOPMENT OF LASER CLADDING WEAR-RESISTANT COATING ON TITANIUM ALLOYS

Laser cladding is an advanced surface modification technology with broad prospect in making wear-resistant coating on titanium alloys. In this paper, the influences of laser cladding processing parameters on the quality of coating are generalized as well as the selection of cladding materials on titanium alloys. The microstructure characteristics and strengthening mechanism of coating are also analyzed. In addition, the problems and precaution measures in the laser cladding are pointed out.

Biological properties of calcium phosphate biomaterials for bone repair: a review

Bone defects are a common disease threatening the health of many people. Calcium phosphate (CaP) is an ideal bone substitutive material that is widely used for bone repair due to its excellent biological properties including osteoinductivity, osteoconductivity and biodegradability. For this reason, investigation of these properties and the effects of various influencing factors is vital for modulating calcium phosphate during the design process to maximally satisfy clinical requirements. In this study, the latest studies on the biological properties of CaP biomaterials, including hydroxyapatite (HA), tricalcium phosphate (TCP), and biphasic calcium phosphate (BCP), have been summarized. Moreover, recent advances on how these properties are altered by different factors are reviewed. Considering the limited mechanical strength of CaP materials, this study also reviews CaP composites with different materials as improvement measures. Finally, perspectives regarding future developments of CaP materials are also provided.

Effect of heating rate on structure of HA coating prepared by sol–gel

Abstract HA coatings were deposited on Ti–6Al–4V alloy substrate using the sol–gel technique. Various heat treatments were carried out and the subsequent effect of heating rate on the resulting coatings was also investigated. The sol–gel derived coatings were studied by X-ray diffraction, electronic probe microanalysis and scratch tester. The results show that the heating rate greatly influences the morphologies, the composition and the adhesion strength of resulting coatings. Under the slow heating rate, the coatings are characterised by high phase purity, compact lamellar structure and less cracks on the surface. Moreover, the scratch test results indicate that the adhesion strength of coatings with slow heating rate is higher than that of coatings with rapid heating rate.

Laser surface remelting and resolidifying process of Zn–27 wt.% Al alloy

Abstract Laser surface remelting and resolidifying process of Zn–27 wt.% Al alloy was studied. Test results showed that alloy microstructure in the remelting zone was greatly refined and homogeneous compared with that in the laser-affected zone and the base material because of the rapid remelting and resolidifying. The hardness of Zn–27 wt.% Al alloy increased greatly compared with that of the base material. The friction and wear features were clearly improved compared with that of the laser-untreated Zn–27 wt.% Al alloy. The mechanism of laser strengthening is also discussed.

Research status of magnesium alloys by micro-arc oxidation: a review

ABSTRACT Magnesium and its alloys are fascinating candidates for biodegradable implants due to their suitable mechanical properties, biodegradability and biocompatibility. However, the rapid corrosion rate, generation of a large amount of hydrogen gas and increase in local pH of the body fluid limit their potential biomedical applications. Various techniques, including alloying, mechanical processing and surface treatment, have been used to reduce the corrosion rate of materials. Surface treatment is one of the widely used techniques to improve the corrosion resistance of the Mg alloys. Compared to other surface modification processes, micro-arc oxidation can provide good adherent, hard, scratch-resistant, wear-resistant, and corrosion-resistant coatings on magnesium alloys. This article mainly reviews the influence of key relatively process parameters, such as electrolytic composition and presence of additives. Normally, electrolytic system and additives can improve the corrosion behaviour of magnesium alloys using appropriate concentration. The future prospects are summarised as well.

Fabrication of Co-Based Coatings on Titanium Alloy by Laser Cladding with CeO2 Addition

In this study, Co-based laser cladding coatings reinforced by multiple phases were fabricated on titanium alloy. Co42 Co-based self-fluxing alloy, B4C, and CeO2 mixed powders were used as the precursor materials. The coatings were mainly composed of γ-Co/Ni, CoTi2, CoTi, NiTi, TiC, Cr7C3, TiB2, and TiB phases. A typical TiB2/Cr7C3/TiC composite structure was chosen. It was found that CeO2 did not influence the phase types of the coating significantly, but was effective in refining the microstructure and enhancing the microhardness and dry sliding wear resistance. Compared with the Ti-6Al-4V titanium alloy, the microhardness and wear resistance of the composite coatings were enhanced by 3.44–4.21 times and 14.26–16.87 times, respectively.