Corrosion and in vitro cytocompatibility investigation on the designed Mg-Zn-Ag metallic glasses for biomedical application

In the present work,seven Mg-Zn-Ag alloys with the nominal composition of Mg_(96-x)Zn_(x)Ag_(4)(x=17,20,23,26,29,32,35 in at.%)were prepared by induction melting and single-roller melt-spinning.The X-ray diffraction(XRD)analyses indicate the metallic glasses with three composition of Mg_(73)Zn_(23)Ag_(4),Mg_(70)Zn_(26)Ag_(4),and Mg_(67)Zn_(29)Ag_(4)were obtained successfully.The differential scanning calorimetry(DSC)measurement was used to obtain the characteristic temperature of Mg-Zn-Ag metallic glasses for the glass-forming ability analysis.The maximum glass transition temperature(Trg)was found to be 0.525 with a composition close to Mg_(67)Zn_(29)Ag_(4),which results in the best glass-forming ability.Moreover,the immersion test in simulated body fluid(SBF)demonstrate the relative homogeneous corrosion behavior of the Mg-Zn-Ag metallic glasses.The corrosion rate of Mg-Zn-Ag metallic glasses in SBF solution decreases with the increase of Zn content.The sample Mg_(67)Zn_(29)Ag_(4)has the lowest corrosion rate of 0.19mm/yr,which could meet the clinical application requirement well.The in vitro cell experiments show that the Madin-Darby canine kidney(MDCK)cells cultured in sample Mg_(67)Zn_(29)Ag_(4)and its extraction medium have higher activity.However,the Mg-Zn-Ag metallic glasses exhibit obvious inhibitory effect on human rhabdomyosarcoma(RD)tumor cells.The present investigations on the glass-forming ability,corrosion behavior,cytocompatibility and tumor inhibition function of the Mg-Zn-Ag based metallic glass could reveal their biomedical application possibility.

The mechanism of external pressure suppressing dendrites growth in Li metal batteries

Li metal is considered an ideal anode material for application in the next-generation secondary batteries.However,the commercial application of Li metal batteries has not yet been achieved due to the safety concern caused by Li dendrites growth.Despite the fact that many recent experimental studies found that external pressure suppresses the Li dendrites growth,the mechanism of the external pressure effect on Li dendrites remains poorly understood on the atomic scale.Herein,the large-scale molecular dynamics simulations of Li dendrites growth under different external pressure were performed with a machine learning potential,which has the quantum-mechanical accuracy.The simulation results reveal that the external pressure promotes the process of Li self-healing.With the increase of external pressure,the hole defects and Li dendrites would gradually fuse and disappear.This work provides a new perspective for understanding the mechanism for the impact of external pressure on Li dendrites.

Investigation on the crystal structure and mechanical properties of the ternary compound Mg_(11-x)Zn_(x)Sr combined with experimental measurements and first-principles calculations

A new ternary compound,Mg_(11-x)Zn_(x)Sr in the Mg-Zn-Sr system was observed and studied using Scanning Electron Microscopy(SEM),Energy-Dispersive Spectroscope(EDS),X-Ray Diffraction(XRD)and Transmission Electron Microscopy(TEM).The XRD patterns were refined by the Rietveld refinement method and the results revealed that the crystallized Mg_(11-x)Zn_(x)Sr phase belonged to tetragonal I41/amd space group and had the Cd_(11)Ba prototype.The Mg atoms were successfully doped into Zn_(11)Sr crystal lattice by occupying Zn atomic sites.Moreover,the Rietveld refinement and computational results demonstrated a gradual decrease in the a-axis and c-axis lattice parameters with decreasing concentration levels of Mg coordination substitution in the lattice of Mg_(11-x)Zn_(x)Sr compound.The elastic constants and modulus of the Mg_(11-x)Zn_(x)Sr compounds calculated by first-principles calculations(FPC)indicated they were increased with the increasing of Zn content.The variation of hardness,D-band widths and the total density of states for Mg_(11-x)Zn_(x)Sr compounds with Zn content was discussed.

Experimental measurement on the phase equilibria of the Mg-Ag-Cu ternary system at 350℃and 400℃

The phase equilibria of the Mg–Ag–Cu ternary system at 350℃and 400℃were experimentally investigated using twenty-eight key samples.The phase equilibria and compositions in key samples were investigated using scanning electron microscopy(SEM)equipped with energydispersive spectroscopy(EDS).Powder X-ray diffraction(XRD)technique was used to analyze the crystal structure and solid solubility of compounds.Five three-phase equilibria and several two-phase equilibria have been determined at 350℃and 400℃.The solid solubility range of Cu in the compounds Mg_(3)Ag,MgAg and fcc(Ag)were examined at 350℃and 400℃.The maximum solid solubility of Ag in the compound MgCu_(2)was found to be 11.46 at.%and 11.25 at.%with a constant value of about 66 at.%Cu at 350℃and 400℃,respectively.Besides,the solid solubility limits of Ag in the compounds Mg_(2)Cu and fcc(Cu)were found to be less than 5 at.%at 350℃and 400℃.No ternary compound was observed in the present work.

Improving superficial microstructure and properties of the laser-processed ultrathin kerf in Ti-6Al-4V alloy by water-jet guiding

In the present research,the gas-assisted laser(GAL)and water-jet guided laser(WGL)processing technologies were applied to machine the ultrathin kerf in the wrought Ti-6Al-4V alloy.The microstructure,microhardness,and wear properties of the superficial layer were investigated.The results reveal that the GAL processing could machine the kerf with a high depth-to-width ratio of 12–15,but the increased processing times enhance the depth little.Due to the oxygen entrainment and relatively low heat and mass transferring efficiency,the assisted gas promotes the formation of a scaled recast layer containingβ-Ti phase and oxides,which increases the roughness to 20μm.The WGL processed kerf has a low depth-to-width ratio with a value of 1.9–2.5 and the depth could be increased by increasing the WGL processing times.With the assistance of the water jet,the remelted debris and heat could be eliminated immediately,which restrains the formation of the recast layer and heat-affected zone.The ultrathin oxide outer layer with hundreds of nanometers and ultrafineα-Ti grain inner layer are formed on the surface,which decreases the roughness to 12μm.Compared with the as-received Ti-6Al-4V alloy,the microhardness of GAL processed kerf surface is increased to 382.8 HV accompanied by residual tensile stress,while the microhardness of WGL processed kerf surface is increased to 481.6 HV accompanying with residual compressive stress.In addition,the GAL processing increases the wear rate at room temperature but decreases the wear rate at high temperatures.Comparatively,the WGL processing decreases the wear rate at room and high temperatures,simultaneously.Such wear behaviors could be ascribed to their different superficial microstructures and phase constituents.

Laser welding process and strength enhancement of carbon fiber reinforced thermoplastic composites and metals dissimilar joint:A review

Carbon fiber reinforced thermoplastic composites(CFRTP)and metals hybrid structures have been widely used in aircraft lightweight manufacturing.However,due to the significant difference in physical and chemical properties between CFRTP and metals,there are lots of challenges to connect them with high quality.Laser welding has a good application prospect in CFRTP and metals connection,and a significant research progress has been made in the exploration of CFRTP-metal laser joining mechanism,joining process optimization,joining strength improvement and joining defects controlling.However,there are still some problems need to be solved for this technology application.In this paper,the research progress of CFRTP-metal laser joining was summarized in three major aspects:theoretical modeling and simulation analysis,process exploration and parameter optimization,joint performance improvement and process innovation.And,problems and challenges of this technology were discussed,and the outlook of this research was provided.

Optimizing mechanical property and cytocompatibility of the biodegradable Mg-Zn-Y-Nd alloy by hot extrusion and heat treatment

The Mg-Zn-Y-Nd alloy is a new type of degradable material for biomedical application. In the present study, Mg-6Zn-1.2Y-0.8Nd alloy was fabricated, and then extrusion and heat treatment were conducted to optimize its mechanical properties and cytocompatibility. The microstructure observation, mechanical property, degradation behavior and cytocompatibility tests were conducted on the Mg-Zn-Y-Nd alloy with three different states: as-cast(alloy C), as-extruded(alloy E) and extruded + heat treated(alloy EH).The results show that alloy C consists of coarse grains and continuous secondary phases. The extrusion process has caused incomplete recrystallization, and results in a mixed grain structure of elongated grains and small equiaxed grains(alloy E). The heat treatment process has promoted the recrystallization and homogenized the grain structure(alloy EH). Both the strength and ductility of the alloy has been improved by extrusion, but the following heat treatment has decreased the strength and increased the ductility.The degradation behavior of the alloy C and E alloys does not show much difference, but improves slightly in alloy EH, because the heat treatment has homogenized the microstructure and released the residual stress in the alloy. The directly and indirectly cell viability tests indicate that alloy EH exhibits the best cytocompatibility, which should be ascribed to its relative uniform degradation and low ion releasing rate. In summary, the combination of hot extrusion and heat treatment could optimize the mechanical property and cytocompatibility of the Mg-Zn-Y-Nd alloy together, which is beneficial for the future application of the alloy.

Deformation and fracture mechanisms of an annealing-tailored "bimodal" grain-structured Mg alloy

Through investigating and comparing the mechanical behavior of an as-rolled Mg-3%Al-1%Zn(wt%)alloy before and after annealing treatments,it was revealed that the formation of annealing-tailored bimodal grain structure ensured the 330℃/4 h samples having a good combination of tensile strength and plasticity.Failure analysis demonstrated that for the as-rolled and 330℃/1 h samples with fine grain structure,their plastic deformation was mainly attributed to basal slips,whereas the deformation mechanism in the bimodal grain-structured samples was dominated by basal slips in fine grains and twinning in coarse grains.For the 330℃/8 h samples with coarse grain structure,high densities of twins were activated.Meanwhile,basal slips occurred in the twinned and un-twinned areas of coarse grains and could pass through twin boundaries.For differently treated samples,cracking preferentially occurred along slip bands,resulting in their transgranular fractures.

Anisotropic corrosion behavior of hot-rolled Mg-8 wt.%Li alloy

By performing the immersion,hydrogen evolution and electrochemical corrosion testing in a 0.1 mol/L NaCl solution,the corrosion performance of differently oriented samples cut from an as-rolled Mg-8wt.%Li alloy plate has been investigated and compared.It demonstrated that obvious anisotropy in corrosion resistance existed between the sample surfaces with different orientations.Among them,the corrosion rate of"ND"(the normal direction)samples with their surfaces perpendicular to the normal direction of the plate was the highest.The corrosion rate of"TD"(the transverse direction)samples with their surfaces perpendicular to the transverse direction of the plate took the second place.For the"RD"(the rolling direction)samples with their surfaces perpendicular to the rolling direction of the plate,they had the lowest corrosion rate.For all the samples,their corrosion performance and the pitting severity were mainly ascribed to the crystallographic texture ofα-Mg matrix phases because the formed surface films onβ-Li phases could provide good protection to the substrate.For the"ND"and"TD"samples,the exposed surfaces were composed of{0002},{1010}and{1120}planes ofα-Mg phases and subsequently resulted in their severe corrosion attack due to the corrosion couples between basal and prism planes.Since the crystallographic planes of exposedα-Mg phases on the surfaces of"RD"samples were mainly{1010}and{1120}prism planes,the pitting severity was the weakest.

Tensile, creep behavior and microstructure evolution of an as-cast Ni-based K417G polycrystalline superalloy

The Ni-based K417G superalloy is extensively applied as aeroengine components for its low cost and good mid-temperature （600-900 ~C） properties. Since used in as-cast state, the comprehensive under-standing on its mechanical properties and microstructure evolution is necessary. In the present research, the tensile, creep behavior and microstructure evolution of the as-cast K417G superalloy under differ-ent conditions were investigated. The results exhibit that tensile cracks tend to initiate at MC carbide and γ＇/γ＇ eutectic structure and then propagate along grain boundary. As the temperature for tensile tests increases from 21 ℃ to 700 ℃, the yield strength and ultimate tensile strength of K417G superalloy decreases slightly, while the elongation to failure decreases greatly because of the intermediate tem- perature embrittlement. When the temperature rises to 900 ℃, the yield strength and ultimate tensile strength would decrease significantly. The creep deformation mechanism varies under different test-ing conditions. At 760 ℃/645 MPa, the creep cracks initiate at MC carbides and γ/γ＇ eutectic structures, and propagate transgranularly. While at 900℃/315 MPa and 950℃/235 MPa, the creep cracks initiate at grain boundary and propagate intergranularly. As the creep condition changes from 760 ℃/645 MPa to 900 ℃/315 MPa and 950 ℃/235 MPa, the γ＇ phase starts to raft, which reduces the creep deformation resistance and increases the steady-state deformation rate.

Effects of icosahedral phase on mechanical anisotropy of as-extruded Mg-14Li (in wt%) based alloys

Through investigating and comparing microstructure and crystallographic texture of as-extruded Mg-14Li and Mg-14Li-6Zn-1Y(in wt%)alloys,the differences in their mechanical anisotropy were investigated.It revealed that the formation of I-phase(Mg3Zn6Y,icosahedral structure)can effectively refine grain size.Moreover,compared with Mg-14Li alloy,the texture type of Mg-14Li-6Zn-1Y alloy changed slightly,but its texture intensity decreased remarkably.As a result,the stronger texture contributed to the"normal"mechanical anisotropy of Mg-14Li alloy with higher tensile strength and a lower elongation ratio along transverse direction(TD)than those along extrusion direction(ED).However,for Mg-14Li-6Zn-1Y alloy,the zonal distribution of I-phase particles along ED caused"abnormal"mechanical anisotropy,i.e.higher tensile strength and better plasticity along ED.

Effect of extrusion process on the mechanical and in vitro degradation performance of a biomedical Mg-Zn-Y-Nd alloy

A new type of biomedical Mg-Zn-Y-Nd alloy was developed and thermal extruded by different processes to investigate the effect of extrusion ratio and extrusion pass on its microstructure,mechanical property and degradation performance.The results show that the increase of extrusion ratio could promote the dynamic recrystallization(DRX)process and led to the coarsening of DRXed grains.While the increase of extrusion pass also contributes to the DRX process but refines the DRXed grains.The simultaneous increasing of extrusion ratio and extrusion pass refines the secondary phases obviously.The increase of extrusion ratio has reduced the tensile strength but improved the elongation of the alloy significantly.However,the increase of extrusion pass could enhance the tensile strength and elongation simultaneously,especially the strength.The degradation performance has been optimized effectively through increasing the extrusion ratio and extrusion pass.

Effect of CaCl_(2) and NaHCO_(3) in Physiological Saline Solution on the Corrosion Behavior of an As-Extruded Mg–Zn–Y–Nd alloy

In this study,the corrosion behaviors of an as-extruded Mg–4%Zn–2%Y–1.8%Nd(in wt.%)alloy in different physiological saline solutions were investigated and compared.The results indicated that the alloy in the 9 g/L NaCl had the higher corrosion resistance than that containing with CaCl_(2) and NaHCO3.Moreover,it demonstrated that the corrosion behaviors of the alloy in two types of solutions were all dependent on the pre-immersion time.In the 9 g/L NaCl solution,the corrosion current densities of the alloy decreased firstly with the pre-immersion time being<4 h and then increased with the pre-immersion time prolonging from 4 to 48 h.However,in the 9 g/L NaCl solution containing with CaCl_(2) and NaHCO3,the corrosion current density of the alloy exhibited the adverse trend with the prolonging the pre-immersion time.Failure analysis demonstrated that the changes of corrosion resistance in two solutions were mainly dominated by the constituents formed in surface films.

M5B3 Boride at the Grain Boundary of a Nickel-based Superalloy

The grain boundary microstructures of a heat-treated Ni-based cast superalloy IN792 were investigated. The results show that M5B3 boride precipitates at the grain boundary. A special orientation relationship between M5B3 phase and the matrix at one side of the grain boundary is found. At the same time, two M5B3 borides with different orientations could co-exist in a single M5B3 particle as an intergrowth besides existing alone, thus forming orientation relationship between the two M5B3 phases and matrix. This phenomenon could be attributed to the special orientation relationship between M5B3 phase and the matrix.

Graphene foam/hydrogel scaffolds for regeneration of peripheral nerve using ADSCs in a diabetic mouse model

The functional recovery of peripheral nerve injury(PNI)is unsatisfactory,whereas diabetes mellitus(DM)and its related complications further attenuate the restoration of diabetic PNI(DPNI).Adipose-derived stem cells(ADSCs)are promising candidates for treatment of DPNI due to their abundant source,excellent differentiation and paracrine ability.Our results showed that ADSCs remarkably enhanced the proliferation and migration of Schwann cells and endothelial cells,and tube formation.Mechanistically,ADSCs could regulate Nrf2/HO-1,NF-κB and PI3K/AKT/mTOR signaling pathways,showing multiple functions in reducing oxidative stress and inflammation,and regulating cell metabolism,growth,survival,proliferation,angiogenesis,differentiation of Schwann cell and myelin formation.In current study,novel graphene foam(GF)/hydrogel-based scaffold was developed to deliver ADSCs for treatment of DPNI.GF/hydrogel scaffold exhibited excellent mechanical strength,suitable porous network,superior electrical conductivity,and good biocompatibility.In vitro results revealed that GF/hydrogel scaffold could obviously accelerate proliferation of Schwann cells.Moreover,in vivo experiments demonstrated that ADSCs-loaded GF/hydrogel scaffold significantly promoted the recovery of DPNI and inhibited the atrophy of targeted muscles,thus providing a novel and attractive therapeutic approach for DPNI patients.