Variable precipitation behaviors of Laves phases in an ultralight Mg-Li-Zn alloy

Precipitation habits plays a decisive role in strengthening materials,especially for Mg alloys the non-basal plane precipitation is necessary but very limited.Generally,the precipitates would nucleate and grow up in a specific habit plane owing to the constraint of free-energy minimization of the system.Herein,in an aged ultralight Mg-Li-Zn alloy,we confirmed that the precipitates dominated by C15 Laves structure could form in a variety of habit planes,to generate three forms of strengthening-phases,i.e.,precipitate-rod,precipitate-lath,and precipitate-plate.Among which,the precipitate-plates are on basal plane as usually but precipitate-rods/laths are on non-basal plane,and such non-basal precipitates would transform into the basal(Mg,Li)Zn_(2)Laves structure with prolonged aging.These findings are interesting to understand the precipitation behaviors of multi-domain Laves structures in hexagonal close-packed crystals,and expected to provide a guidance for designing ultralight high-strength Mg-Li based alloys via precipitation hardening on the non-basal planes.

Grain refinement and strength enhancement in Mg wrought alloys: A review

Low absolute strength becomes one major obstacle for the wider applications of low/no rare-earth(RE) containing Mg alloys. This review firstly demonstrates the importance of grain refinement in improving strength of Mg alloys by comprehensively comparing with other strategy, e.g., precipitation strengthening. Dynamic recrystallization(DRX) plays a crucial role in refining grain size of Mg wrought alloys.Therefore, secondly, the DRX models, grain nucleation mechanisms and the related grain refinement abilities in Mg alloys are summarized,including phase boundary, twin boundary and general boundary induced recrystallization. Thirdly, the newly developed low-RE containing Mg alloy, e.g., Mg-Ce, Mg-Nd and Mg-Sm based alloys, and the RE-free Mg alloys, e.g., Mg-Al, Mg-Zn, Mg-Sn and Mg-Ca based alloy,are reviewed, with the focus on enhancing the mechanical properties mainly via the grain refinement strategy. At the last section, the perspectives and outstanding issues concerning high-performance Mg wrought alloys are also proposed. This review is meant to promote the deep understanding on the critical role of grain refinement in Mg alloys and provide reference for the development of other high strength and low-cost Mg alloys which are fabricated by the conventional extrusion/rolling processing.

Effect of extrusion speed on microstructure and mechanical properties of the Mg-Ca binary alloy

This work reported the effect of extrusion speeds on the microstructures and mechanical properties of Mg-Ca binary alloy.The results showed that yield strength of the as-extruded Mg-1.2wt.%Ca alloys decrease from∼360MPa to∼258MPa as the ram speed increases from 0.4mm/s to 2.4 mm/s,and the elongation increases from∼3.9%to∼12.2%.The microstructure changes from bimodal grain feature to the complete dynamical recrystallization(DRX)with increase of the extrusion speed.The ultrafine DRXed grains in size of∼0.85μm,the numerous nano-Mg_(2)Ca particles dispersing along the grain boundaries and interiors,as well as the high density of residual dislocations,should account for the high strength.It is believed that the high degree of dynamic recrystallization and the resulting texture randomization play the critical roles in the ductility enhancement of the high-speed extruded Mg alloys.

Low-cost and high-strength Mg-Al-Ca-Zn-Mn wrought alloy with balanced ductility

A novel low-cost Mg-Al-Ca-Zn-Mn-based alloy was developed to simultaneously improve its strength and ductility.The high yield strength of 411 MPa and the high elongation to failure of~8.9%have been achieved in the as-extruded Mg-1.3Al-1.2Ca-0.5Zn-0.6Mn(wt%)sample.Microstructure characterizations showed that the high strength is mainly associated with the ultra-fined dynamically recrystallized(DRXed)grains.Moreover,high-density dislocations in the un-DRXed region and nano-precipitates are distributed among theα-Mg matrix.The high ductility property can be ascribed to the high volume fraction of DRXed grains with a much randomized texture,as well as the formations of high-density subgrains in the un-DRXed grain regions.

Mechanism of Mn on inhibiting Fe-caused magnesium corrosion

In the present study,to understand the mechanism of Mn on inhibiting Fe-caused Mg corrosion,the corrosion behaviour of commercial pure Mg and Mg-6 Mn alloy in 0.6 M NaCl solution is investigated.It is found that in Mg-6 Mn alloy,Fe impurity is incorporated into Mn to form Mn(Fe)phase with Fe as solid solute.The initial galvanic corrosion cannot be reduced through converting Fe-rich phase to Mn(Fe)phase,since Mn(Fe)phase also has relatively strong cathodic activity and has much larger volume fraction than Fe-rich phase.However,the cathodic activation behaviour of pure Mg is inhibited.The cathodic activity even decreases for Mg-Mn alloy with increased exposure time,due to the reduced cathodic HER at the Mn(Fe)particles.Mn can be oxidized at the OCP of Mg-6 Mn alloy,resulting in relatively dense Mn-rich corrosion film on particle surface,which separates the particle from the electrolyte and,consequently,inhibits HER.

Enhanced antibacterial activity,corrosion resistance and endothelialization potential of Ti-5Cu alloy by oxygen and nitrogen plasma-based surface modification

Antibacterial Ti-5Cu alloy is a promising substitute material for Ti-made cardiovascular implants,so its surface engineering is crucial to expediting clinical implementation.Given the antibacterial and cardiovas-cular biological benefits of Cu^(2+)and titanium-nitride-oxide(TiN x O y)coatings,a Cu_(2)O/CuO-TiN x O y coating with upregulated Cu^(2+)release was successfully deposited on Ti-5Cu alloy for the first time using oxygen and nitrogen plasma-based surface modification.The superhydrophilic and nanostructured Cu_(2)O/CuO-TiN x O y coating had a dense structure and was well bonded to the substrate,resulting in enhanced cor-rosion resistance,while CuO/Cu_(2)O in the coating released Cu^(2+)faster than Ti_(2)Cu phase in the matrix.More gratifying,the coating demonstrated perfect antibacterial properties(R>99.9%against S.aureus),owing primarily to direct contact sterilization of Cu_(2)O/CuO.The most encouraging phenomenon was that the coating dramatically accelerated HUVEC adhesion(1.4 times),proliferation(RGR:106%-116%),and particularly migration(RMR:158%-247%)compared with the control Ti.The coating extract also signifi-cantly stimulated in vitro angiogenesis capacity.The rapid endothelialization for Cu_(2)O/CuO-TiN x O y coating was attributed to the surface nanostructure and Cu^(2+)/NO_(2)−release,which upregulated the angiogenesis-related gene expression of HIF-1α,VEGF,and eNOS to increase VEGF secretion and NO production.All of the findings indicated that the Cu_(2)O/CuO-TiN x O y coating could enhance the corrosion resistance,an-tibacterial properties,and endothelialization potential of Ti-Cu alloy,displaying great clinical potential in cardiovascular applications.

Microstructure and Mechanical Property of the Large Cross-Sectioned Mg-Gd-Y-Zn-Zr Alloy Produced by Small Extrusion Ratio

In this work,the microstructure and mechanical properties of large cross-sectioned Mg-9Gd-3Y-1.2Zn-0.5Zr(VWZ931)samples produced by the small extrusion ratio has been investigated.The as-extruded VWZ931 sample with diameter of~30 mm can exhibit the high yield strength(YS)of 339 MPa,ultimate tensile strength(UTS)of 387 MPa and elongation of 8.2%,respectively.After peak-aged,the YS and UTS of the Mg samples were significantly increased to 435 MPa and 467 MPa.The small extrusion ratio leads to the low fraction of dynamic recrystallized(DRX)grains in VWZ931 sample,and the texture hardening effect can be fully utilized to achieve high strength.The combined effect of precipitation strengthening due to the long-period stacking ordered phases and theβ′phase,grain boundary strengthening due to the fine DRX grains,heterogeneous deformation-induced strengthening caused by bimodal microstructure,can together contribute to the high strength of present Mg alloy.The findings can shed light on designing other large-sized Mg wrought alloys with high mechanical performance.

Optimal design of high-performance rare-earth-free wrought magnesium alloys using machine learning

In this study,a small dataset of 370 datapoints of Mg alloys are selected for machine learning(ML),in which each datapoint includes five rare-earth-free alloying elements(Ca,Zn,Al,Mn and Sn),three extrusion parameters(extrusion speed,temperature and ratio),and three mechanical properties(yield strength[YS],ultimate tensile strength[UTS]and elongation[EL]).The ML algorithms,including support vector machine regression(SVR),artificial neural network,and other three methods,are employed,and the SVR has the best performance in predicting mechanical properties based on the components,and process parameters,with the mean absolute percentage error of YS,UTS,and EL being 6.34%,4.19%,and 13.64%in the test set,respectively.The SVR model combined with multi-objective genetic algorithm are successfully used to optimize mechanical properties of four extruded alloys from Mg-Ca,Mg-Ca-Zn,Mg-Ca-Mn-Sn,and Mg-Ca-Al-Zn-Mn series alloys,respectively,and the corresponding experimental results are in good agreement with the designed ones.Furthermore,new composition schemes are proposed from a wider range of elements and processing features to match the objectives of high-strength,strength-ductility balanced,and high-ductility Mg alloys,and the four-,five-and six-element alloying schemes are provided for the candidates of new-generation wrought Mg alloys.

Improvement of microstructure and fatigue performance of wire-arc additive manufacture d 4043 aluminum alloy assiste d by interlayer friction stir processing

To expand the application of wire-arc additive manufacturing(WAAM)in aluminum alloy forming com-ponents,it is vitally important to reduce the porosity,refine microstructure,and thereby improve the mechanical properties of the components.In this study,the interlayer friction stir processing(FSP)tech-nique was employed to assist the WAAM of 4043 Al-Si alloy,and the related effects on the microstruc-ture evolutions and mechanical properties of the fabricated builds were systematacially investigated.As compared to the conventional WAAM processing of Al-Si alloy,it was found that the introduction of in-terlayer FSP can effectively eliminate the pores,and both theα-Al dendrites and Si-rich eutectic network were severely broken up,leading to a remarkable enhancement in ductility and fatigue performance.The average yield strength(YS)and ultimate tensile strength(UTS)of the Al-based components produced by the combination of WAAM and interlayer FSP methods were 88 and 148 MPa,respectively.Meanwhile,the elongation(EL)of 37.5%and 28.8%can be achieved in the horizontal and vertical directions,respec-tively.Such anisotropy of EL was attributed to the inhomogeneous microstructure in the stir zone(SZ).Notably,the stress concentration can be effectively reduced by the elimination of porosity and Si-rich eu-tectic network fragmentation by the interlayer FSP,and thus the fatigue behavior was improved with the fatigue strength and elongation increased by∼28%and∼108.7%,respectively.It is anticipated that this study will provide a powerful strategy and theoretical guidance for the WAAM fabrication of Al-based alloy components with high ductility and fatigue performance.

Far-from-equilibrium electrosynthesis ramifies high-entropy alloy for alkaline hydrogen evolution

High-entropy alloys(HEAs)provide an ideal platform for developing highly active electrocatalysts and investigating the synergy of mixed elements.Far-from-equilibrium synthesis holds great potential for fabricating HEAs at the nanoscale by rapidly shifting the thermodynamic conditions and manipulat-ing the growth kinetics.While far-from-equilibrium synthesis of nanomaterials has been successful un-der thermochemical conditions,it is markedly challenging under electrochemical environments,as the use of an electrolyte limits the accessible temperature window and the temporal tunability of tem-perature.Herein,we demonstrate that applying a large electrochemical overpotential would create a far-from-equilibrium condition as changing the temperature of the system by considering the equation △G=△H−T△S+nF△ψ.An electrochemical far-from-equilibrium approach is thus setup for construct-ing hierarchical and self-supporting high-entropy alloy nanostructures.The large overpotential drives the simultaneous reduction of multiple cations and the subsequent formation of a single-phase alloy.As a proof-of-concept,hierarchical Fe_(0.22)Co_(0.18)Ni_(0.18)Cr_(0.14)Cu_(0.28)was fabricated and used as an electrocatalyst for the hydrogen evolution reaction in alkaline media.The noble-metal-free HEA exhibits an overpoten-tial of 84 mV at a current density of 10 mA cm^(-2),which is among the lowest even compared to noble metal-based electrocatalysts.This work opens a new avenue for building a variety of HEAs for energy and catalysis applications.

The role of single-boron of N-doped graphene for effective nitrogen reduction

Room-temperature electrocatalytic nitrogen reduction reaction(NRR)is of paramount significance for the fertilizer industry and fundamental catalysis science.However,many NRR catalysts were based on the use of metals.Herein,we focus on exploring boron-based,metal-free,efficient catalysts for NRR by den-sity functional theory calculations with van der Waals corrections(DFT+D3).Our results show that the NRR performance of the boron active site can be improved by tuning the N-coordination environment in a graphene sheet,and the B-N-C structures show excellent stability.By considering the correlation be-tween the Bader charges of the boron dopant over N-decorated graphene and their NRR activities,the ra-tional design principle of a boron-based catalyst for NRR is developed.The boron-site with one pyridinic nitrogen in a double-vacancy structure is found to be a highly active center,with low reaction energy(0.53 eV)and kinetic barrier(0.84 eV)through the distal mechanism.We also found that the charge loss of boron considerably hampers hydrogen adsorption,which in turn promotes the NRR efficiency by hin-dering the competing hydrogen evolution.This work offers new insights into developing low-cost,highly effective boron-based materials as promising electrocatalysts for green ammonia synthesis.

Two-dimensional interface superstructures assembled by well-ordered solute atoms

Segregation of solutes/impurities in the interfaces plays a decisive role in material performances.However,the segregation of solutes/impurities remains elusive due to the diversity of interfacial structures.Here,in a Mg-Nd-Mn ternary model system,two ordered novel two-dimensional(2D)interfacial superstructures formed by periodic segregation of solute atoms in special symmetric and asymmetric tilt grain boundaries(GBs)have been systematically investigated.Z-Contrast high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)observations provided the atomic-level details on how solute atoms were arranged on these special partially coherent tilt GBs.The strained conditions of each atomic site at the tilt GBs were accurately reproduced by molecular dynamics(MD)simulations plus Voronoi analysis,and the rationality of solute segregation in each atomic-site was evaluated carefully based on the first-principles calculations.These findings expand our knowledge of solute/impurity segregation behaviors in the interfaces,especially the co-segregation behaviors in multi-component materials.

Oxygen promoted hydrogen production from formaldehyde reforming with oxide-derived Cu nanowires at room temperature

This work demonstrates a two-step method to produce oxide-derived Cu nanowires on Cu mesh surface to offer a monolithic catalyst that outstandingly improves the hydrogen production from reforming formaldehyde and water under ambient conditions.Our results not only reveal that the special oxidederived nanostructure can significantly improve the formaldehyde reforming performance of Cu,but also display that the hydrogen production has a linear relationship with oxygen pressure.Specially,a maximum of 36 times increment in hydrogen generation rate is observed than that without oxygen during the reaction.Density functional theory calculations show that the formaldehyde molecule is adsorbed on Cu surface only when the adsorbed oxygen is in adjacency,and hydrogen release process is the ratedetermining step.This work highlights that the activity of deliberately synthesized catalyst can further be promoted by dynamic chemical modulation of surface states during working.

Indirectly extruded biodegradable Zn-0.05wt%Mg alloy with improved strength and ductility： In vitro and in vivo studies

As compared to permanent orthopedic implants for load-bearing applications, biodegradable orthopedic implants have the advantage of no need for removing after healing, but they suffer from the ＂trilemma＂ problem of compromising among sufficiently high mechanical properties, good biocompatibility and proper degradation rate conforming to the growth rate of new bones. In the present work, in vitro and in vivo studies of a Zn-0.05 wt%Mg alloy（namely, Zn-0.05 Mg alloy） were conducted with pure Zn as a control. The Zn-0.05 Mg alloy is composed of a small amount of Mg2 Zn11 phase embedded in the refined Zn matrix with an average grain size of ～20 μm. The addition of 0.05 wt% Mg into Zn significantly increases the ultimate tensile strength up to 225 MPa and the elongation to fracture to 26%, but has little influence on the in vitro degradation rate. Both Zn and Zn-0.05 Mg alloy exhibit homogeneous in vitro degradation with a rate of about 0.15 mm/year. Based on the cytotoxicity evaluation, Zn and Zn-0.05 Mg alloy do not induce toxicity to L-929 cells, indicating that they have little toxicity to the general functions of the animal. An in vivo biocompatibility study of Zn and Zn-0.05 Mg alloy samples by placing them in a rabbit model for 4.12 and 24 weeks, respectively did not show any inflammatory cells, and demonstrated that new bone tissue formed at the bone/implant interface, suggesting that Zn and Zn-0.05 Mg alloy promote the formation of new bone tissue. The in vivo degradation of Zn and Zn-0.05 Mg alloy does not bring harm to the important organs and their cell structures. More interestingly, Zn and Zn-0.05 Mg alloy exhibit strong antibacterial activity against Escherichia coli and Staphylococcus aureus. The above results clearly demonstrate that the Zn-0.05 Mg alloy could be a potential biodegradable orthopedic implant material.

Antibacterial metals and alloys for potential biomedical implants

Metals and alloys,including stainless steel,titanium and its alloys,cobalt alloys,and other metals and alloys have been widely used clinically as implant materials,but implant-related infection or inflammation is still one of the main causes of implantation failure.The bacterial infection or inflammation that seriously threatens human health has already become a worldwide complaint.Antibacterial metals and alloys recently have attracted wide attention for their long-term stable antibacterial ability,good mechanical properties and good biocompatibility in vitro and in vivo.In this review,common antibacterial alloying elements,antibacterial standards and testing methods were introduced.Recent developments in the design and manufacturing of antibacterial metal alloys containing various antibacterial agents were described in detail,including antibacterial stainless steel,antibacterial titanium alloy,antibacterial zinc and alloy,antibacterial magnesium and alloy,antibacterial cobalt alloy,and other antibacterial metals and alloys.Researches on the antibacterial properties,mechanical properties,corrosion resistance and biocompatibility of antibacterial metals and alloys have been summarized in detail for the first time.It is hoped that this review could help researchers understand the development of antibacterial alloys in a timely manner,thereby could promote the development of antibacterial metal alloys and the clinical application.

A novel biomedical titanium alloy with high antibacterial property and low elastic modulus

β-type titanium alloys have attracted much attention as implant materials because of their low elastic modulus and high strength,which is closer to human bones and can avoid the problem of stress fielding and extend the lifetime of prosthetics.However,other issues,such as the infection or inflammation postimplantation,still trouble the titanium alloy's clinical application.In this paper,we developed a novel nearβ-titanium alloy(Ti-13Nb-13Zr-13Ag,TNZA)with low elastic modulus and strong antibacterial ability by the addition of Ag element followed by proper microstructure controlling,which could reduce the stress shielding and bacterial infections simultaneously.The microstructure,mechanical properties,corrosion resistance,antibacterial properties and cell toxicity were studied using SEM,electrochemical testing,mechanical test and cell tests.The results have demonstrated that TNZA alloy exhibited an elastic modulus of 75-87 GPa and a strong antibacterial ability(up to 98%reduction)and good biocompatibility.Moreover,it was also shown that this alloy's corrosion resistance was better than that of Ti-13Nb-13Zr.All the results suggested that Ti-13Nb-13Zr-13Ag might be a competitive biomedical titanium alloy.

Optimization of mechanical properties, biocorrosion properties and antibacterial properties of wrought Ti-3Cu alloy by heat treatment

Previous study has shown that Ti-3Cu alloy shows good antibacterial properties(>90%antibacterial rate),but the mechanical properties still need to be improved.In this paper,a series of heat-treatment processes were selected to adjust the microstructure in order to optimize the properties of Ti-3Cu alloy.Microstructure,mechanical properties,biocorrosion properties and antibacterial properties of wrought Ti-3Cu alloy at different conditions was systematically investigated by X-ray diffraction,optical microscope,scanning electron microscope,transmission electron microscopy,electrochemical measurements,tensile test,fatigue test and antibacterial test.Heat treatment could significantly improve the mechanical properties,corrosion resistance and antibacterial rate due to the redistribution of copper elements and precipitation of Ti2Cu phase.Solid solution treatment increased the yield strength from 400 to 740MPa and improved the antibacterial rate from 33%to 65.2%while aging treatment enhanced the yield strength to 800e850MPa and antibacterial rate(>91.32%).It was demonstrated that homogeneous distribution and fine Ti2Cu phase plays a very important role in mechanical properties,corrosion resistance and antibacterial properties.

Oxygen-sulfur Co-substitutional Fe@C nanocapsules for improving microwave absorption properties

Heteroatom substitution has been investigated to be a feasible way to optimize microwave absorption properties of core-shell structural nanocapsules at gigahertz.Although dielectric capacity has been increased at specific frequency with substituted absorbents,its broadband absorption performance is still relatively poor ascribed to the low dipole oscillation amplitude of single substituted heteroatom.In this study we demonstrate that sulfur and oxygen co-substituted heterostructure leads to high microwave absorption property of core-shell structural Fe@C nanocapsules at broadened frequency range,comparable to the single sulfur substitutional Fe@C nanocapsules.Experimental characterizations coupled with first-principles calculations reveal that the microwave absorption enhancement is triggered by the sulfur-oxygen co-substitution,which results in the serious symmetry breaking and thus leads to the charge separation at the co-substituted area.In particular,the nanocapsules exhibt the minimum reflection loss capcacity R(d B)of-52 d B at 6.8 GHz and the bandwith for R(d B)<-20 dB is in the frequency range of 3.1-12.7 GHz.The present study not only offers a deep insight into the relationship between heteroatom and microwave absorption property,but also puts forward a mentality for further designing microwave absorbents.

Engineering the epitaxial interface of Pt-CeO2 by surface redox reaction guided nucleation for low temperature CO oxidation

The interface between metal nanoparticles(NPs)and support plays a vital role in catalysis because both electron and atom exchanges occur across the metal-support interface.However,the rational design of interfacial structure facilitating the charge transfer between the neighboring parts remains a challenge.Herein,a guided nucleation strategy based on redox reaction between noble metal precursor and supportsurface is introduced to construct epitaxial interfaces between Pt NPs and CeO2 support.The Pt/CeO2 catalyst exhibits near room temperature catalytic activity for CO oxidation that is benefited from the well-defined interface structure facilitating charge transfer from CeO2 support to Pt NPs.Meanwhile,this general approach based on support-surface-induced-nucleation was successfully extended to synthesize Pd and Cu nanocatalysts on CeO2,demonstrating its universal and feasible characteristics.This work is an important step towards developing highly active supported metal catalysts by engineering their interfaces.

Microstructural and mechanical response of ZK60 magnesium alloy subjected to radial forging

Radial forging(RF)is an economical manufacturing forging process,in which four dies arranged radially around the workpiece simultaneously act on the workpiece with high-frequency radial movement.In this study,a ZK60 magnesium alloy step-shaft bar was processed under different accumulated strains by RF at350℃.The deformation behavior,microstructure evolution,and mechanical responses of this bar were systematically investigated via numerical simulations and experiments.At the early deformation stage of forging,the material undergoes pronounced grain refinement but an inhomogeneous grain structure is formed due to the strain gradient along the radial direction.The grains in different radial parts were gradually refined by increasing the RF pass,resulting in a bimodal grained structure comprising coarse(~14.1μm)and fine(~2.3μm)grains.With the RF pass increased,the initial micro-sizeβ-phases were gradually crushed and dissolved into the matrix mostly,eventually evolving to form a higher area fraction of nano-sized Zn2 Zr spheroidal particles uniformly distributed through the grain interior.The texture changed as the RF strain increased,with the c-axes of most of the deformed grains rotating in the RD.Additionally,excellent mechanical properties including higher values of tensile strengths and ductility were attained after the three RFed passes,compared to the as-received sample.