Surface modification of biomedical magnesium alloy wires by micro-arc oxidation

Magnesium alloy wires were processed by micro-arc oxidation （MAO） in a modified silicate-phosphate composite electrolyte containing hydroxyapatite （HA） nanopowders and NaOH. Effects of NaOH content in the composite electrolyte on the microstructure and properties of the MAO ceramic coatings on magnesium alloy wires were studied. It is found that the arc voltage of magnesium alloy wires in the micro-arc oxidation process is significantly reduced while the oxidation rate is accelerated. Addition of 2 g/L NaOH in the composite electrolyte is a better choice for improving corrosion resistance of magnesium alloy wires. During early simulated body fluids （SBF） immersion, the micro-arc oxidized magnesium alloy wires undergo a slow and stable degradation. After soaking for 28 d, the protective ceramic coating still shows no damage but significant degradation is observed for magnesium alloy wires after immersion for more than 60 d.

Preparation,microstructure and degradation behavior of Mg−2Zn−0.4Sc−0.2Zr alloy wire

A biodegradable Mg−2Zn−0.4Sc−0.2Zr(ZK20−0.4Sc)alloy wire with a diameter of 0.5 mm was prepared by a combination of hot extrusion and cold-drawing.The average grain size of ZK20−0.4Sc alloy wire on the longitudinal section along the drawing direction is approximately 7.3μm.The texture results show relatively strong<1020>and weak<1010>fiber texture components parallel to the drawing direction.The ZK20−0.4Sc alloy wire exhibits better mechanical properties with the tensile strength,yield strength and elongate of(329±2)MPa,(287±2)MPa and(14.2±0.5)%,respectively.The better mechanical properties are mainly attributed to the grain refinement strengthening,dislocation strengthening and precipitation strengthening.With the immersion time increasing to 14 d,the corrosion type transfers from filament corrosion and pitting corrosion to severe localized corrosion.

Degradable magnesium alloy suture promotes fibrocartilaginous interface regeneration in a rat rotator cuff transosseous repair model

Despite transosseous rotator cuff tear repair using sutures is widely accepted for tendon-bone fixation,the fibrocartilaginous enthesis regeneration is still hardly achieved with the traditional sutures.In the present work,degradable magnesium(Mg)alloy wire was applied to suture supraspinatus tendon in a rat acute rotator cuff tear model with Vicryl Plus 4±0 absorbable suture as control.The shoulder joint humerus-supraspinatus tendon complex specimens were retrieved at 4,8,and 12 weeks after operation.The Mg alloy suture groups showed better biomechanical properties in terms of ultimate load to failure.Gross observation showed that hyperplastic response of the scar tissue at the tendon-bone interface is progressively alleviated over time in the both Mg alloy suture and Vicryl suture groups.In the histological analysis,for Mg alloy suture groups,chondrocytes appear to proliferate at 4 weeks postoperatively,and the tendon-bone interface showed an orderly structural transition zone at 8 weeks postoperatively.The collagenous fiber tended to be aligned and the tendon-bone interlocking structures apparently formed,where transitional structure from unmineralized fibrocartilage to mineralized fibrocartilage was closer to the native fibrocartilaginous enthesis.In vivo degradation of the magnesium alloy wire was completed within 12 weeks.The results indicated that Mg alloy wire was promising as degradable suture with the potential to promotes fibrocartilaginous interface regeneration in rotator cuff repair.

Exceptional mechanical properties of AZ31 alloy wire by combination of cold drawing and EPT

A 0.66 mm-diameter AZ31 alloy wire with ultimate tensile strength of 400 MPa and elongation of 28.5%was successfully prepared via the combination of cold-drawing and electropulsing treatment processing(EPT).Microstructure observation showed that the grain size of EPTed samples was refined to about 1μm and the basal texture strength with maxima texture index was weakened to 7.18.EPT can significantly accelerate recrystallization by enhancing the mobility of dislocation and atomic diffusion due to the coupling of the thermal and athermal effects.Finally,uniform ultrafine-grained structure was obtained in the EPTed samples by static recrystallization completed in a very short time(30 s)at relatively low temperature(433 K).

Improvement of impact resistance of plain-woven composite by embedding superelastic shape memory alloy wires

Carbon fiber reinforced polymer (CFRP) composites have excellent mechanical properties, specifically, high specific stiffness and strength. However, most CFRP composites exhibit poor impact resistance. To overcome this limitation, this study presents a new plain-woven CFRP composite embedded with superelastic shape memory alloy (SMA) wires. Composite specimens are fabricated using the vacuum-assisted resin injection method. Drop-weight impact tests are conducted on composite specimens with and without SMA wires to evaluate the improvement of impact resistance. The material models of the CFRP composite and superelastic SMA wire are introduced and implemented into a finite element (FE) software by the explicit user-defined material subroutine. FE simulations of the drop-weight impact tests are performed to reveal the superelastic deformation and debonding failure of the SMA inserts. Improvement of the energy absorption capacity and toughness of the SMA-CFRP composite is confirmed by the comparison results.

Corrosion resistance of aluminum alloy AA7022 wire fabricated by friction stir extrusion

Friction stir extrusion(FSE)is known as an innovative manufacturing technology that makes it possible to directly produce wire via consolidation and extrusion of metal chips or solid billets.In this study,wire samples were produced using aluminum alloy AA7022 machining chips by the use of the FSE.To this end,the microstructures and mechanical properties of the base material(BM)and the extruded samples were investigated.The corrosion resistance of the given samples was also determined using potentiodynamic polarization technique.The results showed that the samples manufactured at higher rotational speeds possessed good surface quality,the process temperature and the grain size similarly increased following the rise in rotational speed,and the mechanical properties consequently decreased.Using the FSE led to crystallite refinement,increase in volume fraction of grain boundaries,as well as re-distribution of precipitates affecting corrosion resistance.Furthermore,the findings of the corrosion tests revealed that the produced samples by the FSE had adequate corrosion resistance and the growth in die rotation rate augmented current density and subsequently reduced corrosion resistance.

Improving Performance of Inoculating Alloy Wires by Coating a Boron Nitride Layer

The paper reports the deposition（by magnetron sputtering） and properties of polycrystalline boron nitride （BN） layers on commercial inoculating alloy wires. As is characterized by means of Fourier transform infrared（FTIR） spectroscopy, electron energy dispersive X-ray（EDX） spectroscopy and scanning electron microscopy（SEM）, the thin BN layers consist of hexagonal and orthorhombic BN phases and are smooth without cracks. Organism transfer- ring-circles experiments reveal that the adhesion between the BN layer and alloy wire is very good after tens of cycles. It is demonstrated that the BN layers covered wires are biomaterial lubricious and self-cleaning. As a result, BN layer would effectively enhance the function and efficiency of inoculating alloy wires, which could be widely ap- plied to bio-experimentation and biomedicine apparatuses.

Microstructure and property research on welded joints of 7xxx aluminum alloy welding wire TIG for 7075 aluminum alloy

7 xxx welding wire was self-made by spray forming ingots drawn to series welding wires products,and then TIG butt welding test is used for 5 mm thick 7075 high-strength aluminium alloy.After welding,the stress relief+solid-solution aging heat treatment(T6)were performed to joints,and the mechanical properties and microstructure of the joints before and after heat treatment were comparative analyzed.The results show that the properties of the heat-affected zone(HAZ)of the joint before heat treatment decreas,and the joint is softened.The welded joints tensile strength is 271.8 MPa,the elongation is 5.6%,and the average hardness of the weld is 118.4 HV.The second phase particles such asη(Mg Zn2),S(Al2 Cu Mg),Al13 Fe4 are distributed in a network layer,with no apparent element segregation.After heat treatment,the structure of each area of the joint is coarsened,and a small amount of Fe-containing impurity phases are distributed.Theηand S phases are dissolved in the matrix.The hardness of each area of the joint is increased to 155 HV,and the softening zone is disappeared,this leads the joint elongation close to 16.9%.The tensile strength is increased to 511.8 MPa,reaching 94%of the base metal tensile strength.

Effects of F-Si sealer on electrochemical characteristics of 15%Al-85%Zn alloy thermal spray coating

Most hulls of the ships are protected with paintings, sacrificial anode, and impressed current cathodic protection methods against corrosion problems. However, these conventional methods are not very effective because the rudder of ships stern are exposed to very severe corrosive environment such as tides, speeds of ships, cavitations and erosion corrosion. The environmental factors such as cavitation and corrosion will cause damage for materials with the shock wave by the creation and destruction of bubble. To solve these problems, the cavitation and electrochemical experiments are executed for thermal spray coating with Al-Zn alloy wire material. Thereafter, and sealed specimens with F-Si sealer on Al-Zn alloy coated specimen are executed to improve electrochemical and anti-cavitation characteristics in sea water. The application of fluorine silicon sealing after spray coating of 15%Al-85%Zn seems to be appropriate not only in static environment but also in dynamic environment.

A Flexible Hingeless Control Surface Inspired by Aquatic Animals

A flexible hingeless control surface model was proposed for motion control of Underwater Vehicles (UVs),which is inspiredby the flexible bending control surfaces of underwater creatures,such as fish and squid.Computational Fluid Dynamics(CFD) simulation demonstrates that,in comparison with the hinged or rigid control surface,the proposed flexible bendingcontrol surface can suppress the flow separation so as to improve the turning performance.A prototype of the flexible controlsurface was fabricated,in which Shape Memory Alloy (SMA) wires were selected as the actuators.The elastic energy storageand exchange mechanism was incorporated into the actuation of the control surface to improve the efficiency.Thermal analysisof SMA wires was performed to find proper actuating condition.Open-loop bending experiments were carried out.The resultsshow that the proposed control surface can achieve the maximum bending angle of 104°.Moreover,the power and energyconsumption under different pulse conditions were compared.

Degradation behaviors of surface modified magnesium alloy wires in different simulated physiological environments

The degradation behaviors of the novel high-strength AZ31B magnesium alloy wires after surface modification using micro-arc-oxidization （MAO） and subse- quently sealing with poly-L-lactic acid （PLLA） in different simulated physiological environments were investigated. The results show the surface MAO micropores could be physically sealed by PLLA, thus forming an effective protection to corrosion resistance for the wires. In simulated gastric fluid （SGF） at a low pH value （1.5 or 2.5）, the treated wires have a high degradation rate with a rapid decrease of mass, diameter, mechanical properties and a significant increase of pH value of the immersion fluid. However, surface modification could effectively reduce the degradation rate of the treated wires in SGF with a pH value above 4.0. For the treated wires in simulated intestinal fluid at pH =8.5, their strength retention ability is higher than that in strong acidic SGF. And the loss rate of mass is faster than that of diameter, while the pH value of the immersion fluid decreases. It should be noted that the modified wires in simulated body environment have the best strength retention ability. The wires show the different degradation behaviors indicating their different degradation mechanisms, which are also proposed in this work.

Microstructure and tensile properties of Mo alloy synthetically strengthened by nano-Y_2O_3 and nano-CeO_2

Nano-Y2O3 and nano-CeO2 of different weight ratio mixed with deionizing water were doped into MoO2 powder by liquid-solid doping method. The diameter 1.80 and 0.18 mm alloy wires of Mo-0.3Y, Mo-0.3Ce, and Mo-0.15Y-0.15Ce were prepared through reduction, iso- static pressing, sintering, and drawing. Tensile properties, second phase microstructure and fracture surface appear- ance of wires were analyzed. The better refining effect for Mo alloy powder can be gotten after two kinds of nano- particle oxide doped into MoO2 than only one doped. Nano-Y2O3 and nano-CeO2 have different influences on sintering process. For nano-CeO2, the constraining effect of grain growth focuses on the initial sintering stage, nano- Y2O3 plays refining grains roles in the later densification stage. Nano-Y2O3 is undistorted and keeps intact in the process of drawing; and nano-CeO2 is elongated and bro- ken into parts in the drawing direction. The strengthening effect of nano-Y2O3 and nano-CeO2 keeps the finer grains and superior tensile properties for Mo-0.15Y-0.15Ce wire.

Degradation Behavior of Zn-Cu Stents with Different Coatings in Sodium Chloride Solution

The Zn0.6Cu wires are fabricated into stents for the potential biodegradable application of nasal wound healing.The degradation behavior of Zn0.6Cu stents in 0.9 wt%NaCl at 36.5℃ is evaluated.It shows that the untreated Zn0.6Cu stent experiences severe crevice corrosion with acceleration and autocatalytic effects within the micro-cracks and ruptures at 4.67±1.15 d,with the average corrosion rate of 0.28 mm y^(-1).Fortunately,the anodic polarization(AP)+hydrothermal(H)conversion coating,consisting of ZnCO_(3),Zn(OH)_(2) and ZnO,could inhibit the crevice corrosion significantly by reducing the cathode/anode ratio,extending the rupture time up to 16.50±2.95 d,with the average corrosion rate of 0.14 mm y^(-1).This research indicates that the biodegradable Zn-based stent has some potential applications in nasal wound recovery area.