Junxiu Chen

Surface treatment by high current pulsed electron beam

Abstract Electron beams are becoming an increased subject of interest for materials processing. While continuous electron beams have already found wide applications in drilling, hardening, cutting and welding, the advantage of a pulsed electron beam has just emerged. It generates a high power density up to 108–109 W/cm2 at the target surface. Such a high energy is deposited only in a very thin layer within a short time, and causes superfast processes such as heating, melting and evaporation. A dynamic stress field induced in these processes leads to significant modification effects in the material. The combination of these processes provides the material with improved physicochemical and mechanical properties unattainable with ordinary surface treatment techniques. The present paper reports our recent research work on surface treatment by high-current pulsed electron beam (HCPEB). HCPEB is produced on system ‘Nadezhda-2’ with an energy range of 20–40 kV. A series of pure Al and mold steels were studied. Some of them were pre-coated with C, Cr, Ti or TiN powders. A strong enhanced diffusion effect was revealed: the surface elements diffuse approximately several micrometers in depth into the substrate only after several bombardments. Tribological behaviors of these samples were characterized and significant improvement in wear resistance was found. Finally, TEM analysis reveals the presence of stress waves generated by the coupling of thermal and stress fields, which constitutes the main cause of the enhanced diffusion.

Recent advances on the development of biodegradable magnesium alloys: a review

Magnesium alloys have great potential to be used as biodegradable implant materials. In this review, the biodegradation mechanism of magnesium alloys was illustrated and two methods to improve the corrosion resistance of magnesium alloys, namely, alloying and surface treatment were introduced. In each part, the mechanism of improving corrosion resistance was summarised. Finally, the further development of biomaterial magnesium alloys was predicted in this review.

A Very Sensitive Pressure Sensor on a SOI-on-Cavity Substrate

A new structure combining a beam-diaphragm structure and a SOI-on-cavity substrate was proposed in this paper. Both high sensitivity and good linearity could be achieved due to the stress concentrated structure.

Effect of heat treatment on mechanical and biodegradable properties of an extruded ZK60 alloy

ZK60 magnesium alloy possess good mechanical properties and is a potential biodegradable material. But its high degradation rate is not desirable. In this study the effect of heat treatment on the biodegradable property of ZK60 alloy was investigated. T5 treated, T6 treated, as-cast and as-extruded ZK60 alloys were studied. Microstructure characterization, electrochemical measurement and immersion test were carried out. The results showed that both the mechanical properties and degradation behavior were improved after T5 treatment due to the formation of small and uniformly distributed MgZn phases. The as-cast alloys also exhibited good corrosion resistance. However, the as-extruded and T6 treated samples were severely corroded due to the formation of large amounts of second phases accelerating the corrosion rate owing to the galvanic corrosion. The corrosion resistance of ZK60 alloy was as following: T5 treated > as-cast > T6 treated > as-extruded.

Effect of copper content on the corrosion behaviors and antibacterial properties of binary Mg–Cu alloys

Abstract Biodegradable Mg–Cu alloys have attracted many researchers attention due to their characteristics of osteogenesis, angiogenesis, and long-lasting antibacterial effects. In this paper, the effect of copper content on the corrosion behaviors and antibacterial properties of binary Mg–Cu alloys was studied. Microstructure characterization, immersion test, electrochemical test and antibacterial test were carried out. The results show that with the increase of Cu content, the corrosion rate of Mg–Cu alloys was increased greatly due to the galvanic corrosion between Mg matrix and Mg2Cu intermetallic phase. The corrosion rate of Mg–0·3Cu alloy was almost 10 times as fast as Mg–0·1Cu alloy in 0·9 wt-% NaCl solution. Antibacterial test showed that Mg–Cu alloys could efficiently reduce the viability of Candida albicans with the addition of Cu above 0·1 wt-%. Mg–0·1Cu has good potential to be used as antibacterial implants due to its good corrosion resistance and antibacterial property.

Development of magnesium alloys for biomedical applications: structure, process to property relationship

Abstract Magnesium alloys as biodegradable materials have been used in clinic for coronary stents and bone screws, however the low mechanical properties and fast degradation behaviour still limit their application, which attracted many researches to resolve them. In this review, the development of alloying and plastic deformation to control the composition and microstructure of the alloys and improve the mechanical property and degradation behaviour is introduced. Since the biocompatibility and biodegradation must be considered for the design of new biodegradable magnesium alloys, so the possibility to improve the mechanical properties is much restricted. Higher mechanical properties of magnesium alloys are expected to be reached by more attention on combination of new alloy design, heat treatment and plastic deformation techniques. The development of corrosion resistant magnesium alloys still needs much more studies including the corrosion resistant mechanisms fundamental researches.

Mechanical properties of magnesium alloys for medical application: A review

Magnesium alloys as a class of biodegradable metals have great potential to be used as implant materials, which attract much attention. In this review, the mechanical properties of magnesium alloys for medical applications are summarized. The methods to improve the mechanical properties of biodegradable magnesium alloys and the mechanical behaviors of Mg alloys in biomedical application are illustrated. Finally the challenges and future development of biodegradable magnesium alloys are presented.