Effect of Sn addition on the mechanical properties and bio-corrosion behavior of cytocompatible Mg-4Zn based alloys

The mechanical properties and bio-corrosion behaviors of as-extruded Mg-4Zn alloys after Sn addition were investigated,systemati-cally.A small amount of Sn addition to Mg-4Zn alloy slightly improved the mechanical properties for solid solution strengthening,and significantly controlled the bio-corrosion rates.Sn participating in the outer layer film formation as SnO/SnO_(2)resisted the bio-corrosion proceeding.Especially,Mg-4Zn-1.5Sn alloy,with a weight loss rate of 0.45 mm/y and hydrogen evolution rate of 0.099 mL/cm^(2)/day,showed cytotoxicity grade of 0 to MC3T3-E1 cells.The perfect alliance of cytocompatibility,suitable mechanical properties and low bio-corrosion rate demonstrates that this Mg-4Zn-1.5Sn alloy is a promising biodegradable magnesium alloy for orthopedic implants.

A comparison study of Ce/La and Ca microalloying on the bio-corrosion behaviors of extruded Mg-Zn alloys

The influences of Ca and Ce/La microalloying on the microstructure evolution and bio-corrosion resistances of extruded Mg-Zn alloys have been systematically investigated in the current study.Compared with single Ca or Ce/La addition,the Ca-Ce/La cooperative microalloying results in an outstanding grain refinement,because the fine secondary phase particles effectively hinder the recrystallized grain growth.The coarse Ca2Mg6Zn3 phases promote the formation of Ca3(PO4)2 or hydroxyapatite particles during the immersion process and accelerate the dissolution of the corrosion product film,which destroys its integrity and results in the deterioration of anti-corrosive performance.The Ce/La elements can be dispersed within the conventional Mg7Zn3 phases,which reduce the internal galvanic corrosion between Mg matrix and the secondary phases,leading to an obvious improvement of corrosion resistance.Therefore,the Ca-Ce/La cooperative microalloying achieves a homogenous fine-grained microstructure and improves the protective ability of surface film,which will pave a new avenue for the design of biomedical Mg alloys in the coming future.

Effects of Y on the Microstructure, Mechanical and Bio-corrosion Properties of Mg-Zn-Ca Bulk Metallic Glass

The micro-alloying effects of Y on the microstructure, mechanical properties, and bio-corrosion behavior of Mg69-xZn27Ca4Yx（x= 0, 1, 2 at.%） alloys were investigated through X-ray diffraction, compressive tests,electrochemical treatments, and immersion tests. The Mg69Zn27Ca4 alloy was found to be absolutely amorphous, and its glass-forming ability decreased with the addition of Y. The Mg68Zn27Ca4Y1 alloy exhibited an ultrahigh compressive strength above 1010 MPa as well as high capacity for plastic strain above 3.1%.Electrochemical and immersion tests revealed that these Y-doped MgeZ neC a alloys had good bio-corrosion resistance in simulated body fluid（SBF） at 37℃. The results of the cytotoxicity test showed high cell viabilities for these alloys, which means good bio-compatibility.

Effect of Phase Transformation During Long-Term Solution Treatment on Microstructure,Mechanical Properties,and Bio-corrosion Behavior of Mg–5Zn–1.5Y Cast Alloy

The influence of long-term solution treatment for various intervals on the microstructure,mechanical properties,and corrosion resistance of the as-cast Mg–5Zn–1.5Y alloy was investigated.Variation of secondary phases was studied during solution treatment through thermal analysis test and thermodynamic calculations.Tensile and hardness tests,as well as polarization and immersion tests,were performed to evaluate the mechanical properties and corrosion behavior of the ascast and heat-treated alloy,respectively.Results show that solution treatment transforms I-phaseinto W-phaseas well as dissolves it into the a-Mg matrix to some extent;therefore,the amount of W-phase increases.Moreover,prolonged solution treatment decreases the volume fraction of the phases.In the first stage of solution treatment for 14 h,the tensile properties significantly increase due to the incomplete phase transformation.Although long-term solution treatment sharply decreases the tensile and hardness properties of the alloy,it improves the corrosion resistance due to the transformation of I-phase into W-phase.In fact,it decreases corrosion potential and simultaneously dissolves intermetallic compounds into the a-Mg matrix,resulting in the reduction in galvanic microcells between the matrix and compounds.It is found that the optimum time for long-term solution treatment is 14 h,which improves both corrosion behavior and mechanical properties.

Microstructure refinement,mechanical and biocorrosion properties of Mg–Zn–Ca–Mn alloy improved by a new severe plastic deformation process

In this study,the microstructural evolution,mechanical properties and biocorrosion performance of a Mg–Zn–Ca–Mn alloy were investigated under different conditions of heat treatment,extrusion,one pass and two passes of half equal channel angular pressing(HECAP)process.The results showed significant grain refinement of the homogenized alloy after two passes of HECAP process from 345μm to 2μm.Field emission scanning electron microscopy(FESEM)revealed the presence of finer Mg_(6)Zn_(3)Ca_(2)phase as well asα-Mn phase after HECAP process.The results also showed that mechanical characteristics such as yield strength,ultimate tensile strength and elongation of the HECAPed samples improved by~208%,~144%and~100%compared to the homogenized one,respectively.Crystallographic texture analysis indicated that most of the grains at the surface were reoriented parallel to the(0001)basal plane after HECAP process.Electrochemical corrosion tests and immersion results indicated that the sample with two passes of HEACP had the highest biocorrosion resistance confirming that the basal planes had the lowest corrosion rate compared to the non-basal ones.The mechanical behavior and bio-corrosion evaluation demonstrated that the HECAPed Mg–Zn–Ca–Mn alloy has great potential for biomedical applications and a mechanism was proposed to explain the interrelations between the thermomechanical processing and bio-corrosion behavior.

Ti-Zr-Cu-Fe-Sn-Si-Ag-Ta bulk metallic glasses with good corrosion resistance as potential biomaterials

Ti47Cu38-xZr7.5Fe2.5Sn2 Si1 Ag2 Tax(x=1-4;at%,the same below)bulk metallic glasses(BMGs)with good bio-corrosion resistance and mechanical properties were fabricated by copper mold casting.Critical diameter of the Ti-based BMGs with 1 at%-4 at%Ta was 3 mm.The Ta-incorporated Ti-based BMGs exhibit higher open current potential and parallel passive current density in comparison with those of Ti-6 Al-4 V alloy in 0.9 wt%NaCl and Hank’s solution,implying their good corrosion resistance.The pitting corrosion potential of the Ti-based BMGs gradually increases up to about 1.25 V with Ta addition increasing up to 4 at%in 0.9 wt%NaCl solution.Among the present Ti-based BMGs,the alloy bearing2 at%Ta exhibits the optimal integration of mechanical properties,including the compressive fracture strength exceeding 2000 MPa,relative low Young’s modulus of98 GPa,plastic strain of 3.4%and high hardness of HV599.The Ta-bearing Ti-based bulk metallic glasses with integration of relative high GFA,good mechanical properties and high bio-corrosion resistance are beneficial for biomedical applications.

Effect of trace HA on microstructure, mechanical properties and corrosion behavior of Mg-2Zn-0.5Sr alloy

Effect of the addition of trace HA particles into Mg-2Zn-0.5Sr on microstructure, mechanical properties, and bio-corrosion behavior was investigated in comparison with pure Mg. Microstructures of the Mg-2Zn-0.5Sr-xHA composites （x= 0, 0.1 and 0.3 wt%） were characterized by optical microscopy （OM）, scanning electron microscopy （SEM） equipped with energy dispersion spectroscopy （EDS） and X-ray diffraction （XRD）. Results of tensile tests at room temperature show that yield strength （YS） of Mg- 2Zn-0.5Sr/HA composites increases significantly, but the ultimate tensile strength （UTS） and elongation decrease with the addition of HA particles from 0 up to 0.3 wt%. Bio-corrosion behavior was investigated by immersion tests and electrochemical tests. Electrochemical tests show that corrosion potential （Ecorr） of Mg-2Zn-0.5Sr/HA composites significantly shifts toward nobler direction from -1724 to -1660 mVscE and the corrosion current density decreases from 479.8 to 280.8 p.Acm^-2 with the addition of HA particles. Immersion tests show that average corrosion rate of Mg-2Zn-0.BSr/HA composites decreases from 11.7 to 9.1 mm/year with the addition of HA particles from 0 wt% up to 0.3 wt%. Both microstructure and mechanical properties can be attributed to grain refinement and mechanical bonding of HA particles with second phases and α-Mg matrix. Bio-corrosion behavior can be attributed to grain refinement and the formation of a stable and dense CaHPO4 protective film due to the adsorption of Ca^2＋ on HA particles. Our analysis shows that the Mg-2Zn-0.5Sr/0.3HA with good strength and corrosion resistance can be a good material candidate for biomedical applications.

Osteogenesis and angiogenesis of a bulk metallic glass for biomedical implants

Implantation is an essential issue in orthopedic surgery.Bulk metallic glasses(BMGs),as a kind of novel materials,attract lots of attentions in biological field owing to their comprehensive excellent properties.Here,we show that a Zr_(61)Ti_(2)Cu_(25)Al_(12)(at.%)BMG(Zr-based BMG)displays the best cytocompatibility,pronounced positive effects on cellular migration,and tube formation from in-vitro tests as compared to those of commercial-pure titanium and poly-ether-ether-ketone.The in-vivo micro-CT and histological evaluation demonstrate the Zr-based BMG can significantly promote a bone formation.Immunofluorescence tests and digital reconstructed radiographs manifest a stimulated effect on early blood vessel formation from the Zr-based BMG.Accordingly,the intimate connection and coupling effect between angiogenesis and osteogenesis must be effective during bone regeneration after implanting Zr-based BMG.Dynamic gait analysis in rats after implanting Zr-based BMG demonstrates a tendency to decrease the pain level during recovery,simultaneously,without abnormal ionic accumulation and inflammatory reactions.Considering suitable mechanical properties,we provide a realistic candidate of the Zr61Ti2Cu25Al12 BMG for biomedical applications.