Improved Corrosion Behavior of Biodegradable Mg-4Zn-1Mn Alloy Modified by Sr/F co-doped CaP Micro-arc Oxidation Coatings

The Sr/F co-doped CaP(Sr/F-CaP)coatings were prepared by micro-arc oxidation(MAO)under different voltages to modify the microstructure and corrosion behavior of Mg-4Zn-1Mn alloy.The surface and interface characteristics investigated using scanning electron microscopy(SEM)and energy dispersive X-ray spectrometer(EDS)showed that the MAO coatings displayed uneven crater-like holes and tiny cracks under lower voltage,while they exhibited relatively homogeneous crater-like holes without cracks under higher voltage.The thickness of MAO coatings increased with increasing voltage.The corrosion behavior of Mg-4Zn-1Mn alloy was improved by the MAO coatings.The MAO coatings prepared under 450 V and 500 V voltages possessed the best corrosion resistance with regard to the electrochemical corrosion tests and immersion corrosion tests,respectively.The MAO coatings fabricated under 450-500 V could provide a better corrosion protection effect for the substrate.

Improvement of microstructure,mechanical properties,and corrosion resistance of WE43 alloy by squeeze casting

The WE43 magnesium alloy was prepared by squeeze casting,and the influence of squeeze casting parameters on mechanical properties and corrosion resistance was studied and compared with gravity casting.The gravity cast WE43 alloy shows uneven grain size distribution,and some grains even greater than 90μm.While,the grain size of the squeeze cast WE43 alloy is mainly distributed in 20-50μm.The Mg12Nd2Y phase morphology changes from large lamellar to strips after squeeze casting,whereas Mg_(24)Y_(5) phase exhibits no obvious change.The yield strength,tensile strength,and elongation of the gravity cast WE43 alloy are 127 MPa,157 MPa,and 6%,respectively,and 145 MPa,193 MPa,and 9.1%for squeeze cast alloy.For the squeeze cast WE43 alloy,the average corrosion rate is 0.6056 mm·year^(-1) according to immersion test results,and according to electrochemical measurements,the corrosion current density is 78.13μA·cm^(-2),which is better than that of the gravity cast WE43 alloy.Compared with gravity casting,the grains and second phase of the WE43 alloy by squeeze casting are refined,and the mechanical properties and corrosion resistance are improved.This may expand the applications of the WE43 alloy.

Deformation behavior of a TiZr-based metallic glass composite containing dendrites in the supercooled liquid region

The deformation behavior of a TiZr-based bulk metallic glass composite(BMGC)was characterized in the supercooled liquid region(SLR)from 623 K to 693 K.It was observed that the alloy exhibits the deformation behavior from work softening at low temperatures to work hardening at high temperatures.The yield stress and overshoot stress decrease remarkably with the increase of temperature,accompanied by superplasticity.The results showed that the crystallization occurred in the amorphous matrix for the post-deformation samples and the volume fraction of the corresponding crystallization products increased with increasing testing temperature.It is implied that the work hardening behavior was closely associated with the crystallization of the amorphous matrix.The tensile stress can accelerate the crystallization of amorphous matrix and the martensitic transformation of dendrite phases,which implies that the thermal stability of the alloy decreases under tension.These findings shed light on designing new BMGCs with high mechanical performance as well as the good SLR formability.

Recent development in the application of bulk metallic glasses

Over the past decades,considerable efforts have been made in the commercial application of bulk metallic glasses(BMGs).Despite great challenges faced by the industrial players,significant progress has been achieved,and millions of commercial products for various kinds of applications have been shipped around the world.Here in this paper,we shall present the alloys suitable for the actual products in the application and discuss the merits of the processing technique of BMGs over the existing processing techniques and materials.Most importantly we demonstrate the typical examples of products over the past few years.Finally,future directions of the industrialization of BMGs are also discussed.

Fe-based metallic glass:An efficient and energy-saving electrode material for electrocatalytic degradation of water contaminants

Excessive consumption of electrical energy has hampered the widespread application of electrochemical technology for degradation of various contaminants. In this paper, a Fe-based metallic glass(MG) was demonstrated as a new type of electrocatalyst to effectively and economically degrade an azo dye. In comparison to other typical electrodes, Fe-based MG electrodes exhibit a minimized degradation time, and the specific energy is 4-6 orders of magnitude lower than that of dimensionally stable anode(DSA), metal-like boron-doped diamond(BDD) and other electrodes. As sacrificial electrode materials, Fe-based MGs have less specific electrode mass consumption than iron electrodes. The use of Fe-based MGs will promote the practical application of electrochemical technology and the use of MGs as functional materials.

In Vitro Study on Mg-Sn-Mn Alloy as Biodegradable Metals

The mechanical properties, chemical properties and biocompatibility of Mg-3Sn-0.5Mn alloy were tested. A series of in vitro evaluations such as tensile test, static and dynamic immersion test, hemocompatibility test as well as cytotoxicity test were presented, with commercial magnesium alloy WE43 as the control. Mg-3Sn-0.5Mn alloy possesses suitable strength and superior ductility compared with WE43 and AZ31. Static immersion and dynamic degradation tests showed more uniform degradation with a more moderate rate for Mg-3Sn-0.5Mn alloy （0.34 mm/y in static condition and 0.25 mm/y in dynamic condition） compared with WE43 alloy （0.42 mm/y in static condition and 0.33 mm/y in dynamic condition） in Hank＇s solution. Blood compatibility evaluation suggested that Mg-3Sn-0.5Mn alloy had no destructive effect on erythrocyte and showed excellent anti-thrombogenicity to blood system. Besides, Mg-3Sn-0.5Mn alloy showed no inhibition effect to L929 metabolic activity and mild toxicity to vascular smooth muscle cell （VSMC） in preliminary cell viability assessment. By considering its excellent mechanical strength, corrosion resistance, low ion release rate and good biocompatibility, Mg-3Sn-0.5Mn alloy may be a promising economical candidate as biomedical implant material for load-bearing clinical applications in the future.

Fabrication and Characterization of Ca-Mg-P Containing Coating on Pure Magnesium

A biodegradable Ca-P coating mainly consisting of β-tricalcium phosphate （β-TCP） was fabricated on pure magnesium via the chemical deposition in a simulated Hank’s solution. The method significantly accelerated the coating formation on magnesium. Moreover, the morphology, phase/chemical composition, the coating formation mechanism as well as degradation behavior in phosphate buffered saline （PBS） solution were in- vestigated. Scanning electron microscopy （SEM） images showed that the coating had three layers and X-ray diffraction （XRD） patterns showed that the coating mainly contained Ca3（PO4）2 and （Ca,Mg）3（PO4）2. Elec- trochemical test showed that the corrosion current density （Icorr） of the coated Mg was decreased by about one order of magnitude as compared to that of pure magnesium. The immersion test indicated that the coating could obviously reduce the degradation rate.

Corrosion mechanisms of Zr-based bulk metallic glass in NaF and NaCl solutions

So far,some investigations related to the corrosion mechanism of Zr-based metallic glasses in solutions containing Cl-have been developed.However,few attentions have been paid to the situation in F--containing solution.This paper describes the corrosion behaviours of Zr52Al10Ni6Cu32 bulk metallic glass(BMG)in Na F and Na Cl aqueous solutions.The corrosion mechanism of Zr-based BMG in F–containing solution was proposed for the first time.It was found that in Na Cl solutions,Zr-based BMG samples underwent typical pitting corrosion.Selective dissolution of Zr,Al and enrichment of Cu were observed in corrosion pits.However,corrosion occurred in the form of general breakdown of passive film in Na F solutions.Such difference is interpreted in terms of the binding ability of anions to surrounding molecules,i.e.,Cl-with loose surrounding water passes through the passive film to cause pitting;F-with a tight surrounding molecules layer absorbs on passive film then coordinates with cations from matrix.

Deformation behavior of Ta wire-reinforced Zr-based bulk metallic glass composites

A Ta wire-reinforced Zr-based bulk metallic glass composite with a new type of structure was prepared successfully by the method of liquid metal infiltration. Ta wires distribute uniformly in the metallic glass matrix in the form of spirals. The composite exhibits two yield stages under compressive stress, and the samples are compressed into thin pancakes. The micro-cracks originate at the interface between the Ta wire and the metallic glass matrix and propagate perpendicularly to the interface, which then induce multiple shear bands in the metallic glass matrix due to the stress concentration. Shear cracks form in the metallic glass matrix during the continued loading process as a result of the interaction of shear bands. Deformation bands of Ta wires occur under the impact of shear bands. The local stress fields in the composite are changed obviously due to the introduction of the spiral-formed reinforcements. The investigation of the deformation behavior and mechanism suggests a new method for the application of bulk metallic glass composites as the structural materials.

High-temperature Mechanical Properties and Dynamic Recrystallization Mechanism of in situ Silicide-reinforced MoNbTaTiVSi Refractory High-entropy Alloy Composite

The hypoeutectic composite material composed of BCC phase and in situ precipitated Ti_(5)Si_(3) was prepared by adding Si into MoNbTaTiV high-entropy alloy.The obvious oriented in situ Ti_(5)Si_(3) phase formed eutectic phase with BCC phase in the inter-dendritic area,which leads to excellent properties of the composite.The alloy exhibits ultra-high yield stress of 718 MPa at 1200℃ and obvious compression plasticity.After reaching the maximum strength,dynamic recovery(DRV)and dynamic recrystallization(DRX)caused soften phenomena.The DRX mechanism of the dual-phase eutectic structure is analyzed by electron backscatter diffraction.The DRX of the BCC phase conforms to the discontinuous DRX and continuous DRX mechanisms,while the Ti_(5)Si_(3) phase has a geometric DRX mechanism in addition to the above two mechanisms.The high performance of this composite has enough potential high-temperature applications such as nuclear and aero engine.

Evaluation of the performance of Ca-deficient hydroxyapatite(CDHA)/MgF_(2)bilayer coating on biodegradable high-purity magnesium in a femoral condyle defect model in rabbits

The two most critical factors in promoting the clinical translation of magnesium(Mg)are reducing its degradation rate and improving its osteogenesis.In this study,a Ca-deficient hydroxyapatite(CDHA)/MgF_(2)bilayer coating was prepared on high-purity magnesium(HP Mg)rods by fluorination and hydrothermal treatment.Scanning electron microscope showed that the thickness of the bilayer coating was 3.78 lm and that the surface morphology was nanoscale.In an in vivo experiment on femoral condyle defects in rabbits,the serum magnesium ion levels of rabbits were always in the normal range after surgery,and the liver and kidney functions were not abnormal,which indicated that the CDHA/MgF_(2)bilayer coating has good biosafety.Micro-CT showed that the CDHA/MgF_(2)bilayer coating significantly reduced the degradation rate of the HP Mg rods and enhanced the promotion of bone formation.Hard tissue sections showed that the CDHA/MgF_(2)bilayer coating gave the bone tissue a tight contact interface with the HP Mg rod and improved the bone mass.Immunohistochemistry showed that the expression of vascular endothelial growth factor and BMP-2 was more obvious.These results confirm that the CDHA/MgF_(2)bilayer coating can improve the properties of HP Mg and provide a basis for the further transformation of HP Mg in the future.It also provides a new reference for the surface modification of magnesiummetal.

Biofunctional magnesium coating of implant materials by physical vapour deposition

The lack of bioactivity of conventional medical materials leads to low osseointegration ability that may result in the occurrence of aseptic loosening in the clinic.To achieve high osseointegration,surface modifications with multiple biofunctions including degradability,osteogenesis,angiogenesis and antibacterial properties are required.However,the functions of conventional bioactive coatings are limited.Thus novel biofunctional magnesium(Mg)coatings are believed to be promising candidates for surface modification of implant materials for use in bone tissue repair.By physical vapour deposition,many previous researchers have deposited Mg coatings with high purity and granular microstructure on titanium alloys,polyetheretherketone,steels,Mg alloys and silicon.It was found that the Mg coatings with high-purity could considerably control the degradation rate in the initial stage of Mg alloy implantation,which is the most important problem for the application of Mg alloy implants.In addition,Mg coating on titanium(Ti)implant materials has been extensively studied both in vitro and in vivo,and the results indicated that their corrosion behaviour and biocompatibility are promising.Mg coatings continuously release Mg ions during the degradation process,and the alkaline environment caused by Mg degradation has obvious antibacterial effects.Meanwhile,the Mg coating has beneficial effects on osteogenesis and osseointegration,and increases the new bone-regenerating ability.Mg coatings also exhibit favourable osteogenic and angiogenic properties in vitro and increased long-term bone formation and early vascularization in vivo.Inhibitory effects of Mg coatings on osteoclasts have also been proven,which play a great role in osteoporotic patients.In addition,in order to obtain more biofunctions,other alloying elements such as copper have been added to the Mg coatings.Thus,Mg-coated Ti acquired biofunctions including degradability,osteogenesis,angiogenesis and antibacterial properties.These novel multi-functional Mg coatings are expected to significantly enhance the long-term safety of bone implants for the benefit of patients.This paper gives a brief review of studies of the microstructure,degradation behaviours and biofunctions of Mg coatings,and directions for future research are also proposed.

Effects of Ti addition on corrosion behavior of Zr-based metallic glass in chloride medium

The effects of Ti element on the corrosion resistance of the metallic glass Zr51.3AlloNi6Cu31.8Ag0.lY0.8 in aqueous solution with various chloride concentrations were investigated, and the effect mechanism was discussed. X-ray diffraction con-firmed that Ti-added Zr51.3All0Ni6Cu31.8Ag0.lY0.8 metallic glasses with diameter of 3 mm were all metallic glasses. Weight loss and electrochemical method were introduced to characterize their corrosion resistance, and X-ray photo-electron spectroscopy study was used t9 characterize the passive film composition. The results show that the corrosion resistance of metallic glass is significantly improved with Ti addition, and Zr dioxides dominate in passive film during corrosion when Ti content is low. High Ti addition can lead to an obvious accumulation of Ti dioxides, which results in a thicker, Ti-enriched protective passive film.