四肢组织工程骨新型支架的比较研究

现代医学的骨组织工程中，种子细胞、生物材料和组织构建是三个最基本要素，而生物材料或支架材料是影响组织构建最为关键的因素之一。它必须具有良好的生物相容性、可降解性、低免疫原性以及一定的空间结构、孔隙率、降解速率等特性。

Recent research and developments on wrought magnesium alloys

Wrought magnesium alloys attract special interests as lightweight structural material due to their homogeneous microstructure and enhanced mechanical properties compared to as-cast alloys.In this contribution,recent research and developments on wrought magnesium alloys are reviewed from the viewpoint of the alloy design,focusing on Mg-Al,Mg-Zn and Mg-rare earth(RE)systems.The effects of different alloying elements on the microstructure and mechanical properties are described considering their strengthening mechanisms,e.g.grain refinement,precipitation and texture hardening effect.Finally,the new alloy design and also the future research of wrought magnesium alloys to improve their mechanical properties are discussed.

Role of multi-microalloying by rare earth elements in ductilization of magnesium alloys

The present work investigates the influences of microalloying with rare earths on the mechanical properties of magnesium alloys.The amount of each rare earth element is controlled below 0.4 wt.%in order not to increase the cost of alloy largely.The synergic effects from the multi-microalloying with rare earths on the mechanical properties are explored.The obtained results show that the as-cast magnesium alloys multi-microalloying with rare earths possesses a quite high ductility with a tensile strain up to 25-30%at room temperature.Moreover,these alloys exhibit much better corrosion resistance than AZ31 alloy.The preliminary in situ neutron diffractions on the deformation of these alloys indicate that the multi-microalloying with rare earths seems to be beneficial for the activation of more slip systems.The deformation becomes more homogeneous and the resultant textures after deformation are weakened.

Influence of Ce addition on microstructure and mechanical properties of high pressure die cast AM50 magnesium alloy

The influence of Ce addition on the microstructure and mechanical properties of AM50 magnesium alloy was investigated to improve its mechanical properties.The results show that the addition of Ce to AM50 alloy results in the grain refinement and the mechanical properties of the Ce-modified AM50 at room and elevated temperatures are remarkably improved.AM50 magnesium alloy containing 1% Ce（mass fraction） shows better refinement and mechanical properties compared with the AM50 magnesium alloy with 0.5% Ce and even AM50 alloy without any Ce.

Unexpected formation of hydrides in heavy rare earth containing magnesium alloys

Mg–RE(Dy,Gd,Y)alloys show promising for being developed as biodegradable medical applications.It is found that the hydride REH_(2) could be formed on the surface of samples during their preparations with water cleaning.The amount of formed hydrides in Mg–RE alloys is affected by the content of RE and heat treatments.It increases with the increment of RE content.On the surface of the alloy with T4 treatment the amount of formed hydride REH_(2) is higher.In contrast,the amount of REH2 is lower on the surfaces of as-cast and T6-treated alloys.Their formation mechanism is attributed to the surface reaction of Mg–RE alloys with water.The part of RE in solid solution in Mg matrix plays an important role in influencing the formation of hydrides.

Understanding effects of microstructural inhomogeneity on creep response-New approaches to improve the creep resistance in magnesium alloys

Previous investigations indicate that the creep resistance of magnesium alloys is proportional to the stability of precipitated intermetallic phases at grain boundaries.These stable intermetallic phases were considered to be effective to suppress the deformation by grain boundary sliding,leading to the improvement of creep properties.Based on this point,adding the alloying elements to form the stable intermetallics with high melting point became a popular way to develop the new creep resistant magnesium alloys.The present investigation,however,shows that the creep properties of binary Mg-Sn alloy are still poor even though the addition of Sn possibly results in the precipitation of thermal stable Mg_(2)Sn at grain boundaries.That means other possible mechanisms function to affect the creep response.It is finally found that the poor creep resistance is attributed to the segregation of Sn at dendritic and grain boundaries.Based on this observation,new approaches to improve the creep resistance are suggested for magnesium alloys because most currently magnesium alloys have the commonality with the Mg-Sn alloys.

Influence of incorporating Si_(3)N_(4) particles into the oxide layer produced by plasma electrolytic oxidation on AM50 Mg alloy on coating morphology and corrosion properties

The influence of incorporating different sizes of Si_(3)N_(4) particles on the microstructure and corrosion properties of a phosphate-based plasma electrolytic oxidation (PEO) coating on AM50 magnesium alloy was investigated. The experiments for this study were performed in alkaline electrolytes containing 1 g/L KOH, 10 g/L Na_(3)PO_(4) with and without three different sized of Si_(3)N_(4) particles. The corrosion properties of PEO coatings were investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in 0.5 wt.% NaCl solution. Microstructure observations by SEM showed that the surface morphology and composition of the PEO coating were affected greatly by particle addition. Si_(3)N_(4) particles can still be found without decomposition in the final coating due to their high melting point.

Corrosion behaviour of as-cast ZK40 with CaO and Y additions

The microstructures of as-cast ZK40,ZK40 with 2%(mass fraction)CaO and ZK40 with 1%(mass fraction)Y were investigated,and the intermetallic phase morphology and the distribution were characterised.By having discrete intermetallic particles at the grain boundaries for the ZK40,the microstructure was modified to a semi-continuous network of intermetallic compounds along the grain boundaries for the ZK40 with CaO or Y additions.The CaO was not found in the microstructure.However,Ca was present in Ca2Mg6Zn3 intermetallic compounds which were formed during casting.Hydrogen evolution and electrochemical impedance spectroscopy tests revealed that the addition of CaO slightly enhanced the corrosion resistance whereas Y had a negative effect on the corrosion resistance of ZK40.Immersion tests showed that severe localised corrosion as well as corrosion along the intermetallic compounds played an important role in the corrosion process of ZK40-Y whereas the localised corrosion was not pronounced for ZK40 or ZK40?CaO alloys.Micro-segregation in theα-Mg matrix was notably higher for the ZK40 alloy compared with the modified alloys.The combination of this effect with a possible formation of a more stable corrosion layer for the ZK40-CaO was attributed as the main reason for an improved corrosion resistance for the ZK40-CaO alloy.

Development and prospects of degradable magnesium alloys for structural and functional applications in the fields of environment and energy

Magnesium and its alloys have such advantages with lightweight, high specific strength, good damping, high castability and machinability,which make them an attractive choice for applications where weight reduction is important, such as in the aerospace and automotive industries.However, their practical applications are still limited because of their poor corrosion resistance, low high temperature strength and ambient formability. Based on such their property shortcomings, recently degradable magnesium alloys were developed for broadening their potential applications. Considering the degradable Mg alloys for medical applications were well reviewed, the present review put an emphasis on such degradable magnesium alloys for structural and functional applications, especially the applications in the environmental and energy fields. Their applications as fracture ball in fossil energy, sacrificial anode, washing ball, and as battery anodes, transient electronics, were summarized. The roles of alloying elements in magnesium and the design concept of such degradable magnesium alloys were discussed. The existing challenges for extending their future applications are explored.

Influence of Ca addition on the dynamic and static recrystallization behavior of direct extruded flat profiles of Mg-Y-Zn alloy

This paper investigates the influence of addition of Ca in a Y-Zn-containing magnesium alloy on the dynamic and static recrystallization behaviors and reveals the formation mechanism of the quadrupole texture during thermomechanical processing. Direct extrusion of flat bands has been conducted at various process conditions to study the difference between the two alloys WZ10 and WZX100 in terms of microstructure and texture development. It can be shown that, Ca addition promotes the DRX of WZ10 alloy. During additional heat treatment,the absence of Y segregation at the grain boundaries and the associated lack of solute drag to the boundary mobility leads to a pronounced grain growth during SRX in WZX100 alloy. Furthermore, it is shown that the addition of Ca to Y-Zn is not beneficial in terms of formability.It is demonstrated that alloying elements can have different effects depending on the recrystallization mechanisms. Partially recrystallized microstructure is a prerequisite at the as-extruded status to form the quadrupole texture and during subsequent annealing, which stands for high formability.

Recycling of magnesium drive train components

With the development of new heat resistant magnesium alloys, the automotive industry has introduced several parts to the drive train. The rising number of large magnesium components will result in a higher quantity of automotive post consumer scrap. It was the aim of this work to find a reasonable alloy system for the recycling of these magnesium drive train components. A matrix of potential recy-cling alloys based on the magnesium alloy AM50 was prepared via permanent mould casting. The materials were investigated via tensile testing, creep tests and salt spray tests. Three alloys were selected for processing via high pressure die casting and the tests were repeated on the new materials. A promising system for recycling has been isolated and will be investigated more deeply for the influence of impurities.