查看更多>>摘要：In order to compare the workability of AZ110 alloy with and without addition of La-rich Mish Metal(MM),hot compression tests were performed on a Gleeble-3500D thermo-mechanical simulator at the deformation temperature range of 473-623 K and strain rate range of 0.001-1 s-1.The flow stress,con-stitutive relation,DRX kinetic model,processing map and microstructure characterization of the alloys were investigated.The results show that the flow stress is very sensitive to deformation temperature and strain rate,and the peak stress of AZ110LC(LC = La-rich MM)alloy is higher than that of AZ110 alloy.The hot deformation behavior of the alloys can be accurately predicted by the constitutive relations.The derived constitutive equations show that the calculated activation energy Q and stress exponent n for AZ110 alloy are higher than the calculated values of AZ110LC alloy.The analysis of DRX kinetic models show that the development of DRX in AZ110LC alloy is earlier than AZ110 alloy at the same deforma-tion condition.The processing maps show that the workability of AZ110LC alloy is significantly more excellent than AZ110 alloy and the microstructures are in good agreement with the calculated results.The AZ110LC alloys can obtain complete DRX microstructure at high strain rate due to its higher stored energy and weak basal texture.
查看更多>>摘要：NiTi/Stainless Steel(SS)sheets have been welded via a vacuum electron beam welding process,with three methods(offsetting electron beam to SS side without interlayer,adding Ni interlayer and adding FeNi interlayer),to promote mechanical properties of the NiTi/SS joints.The joints with different interlayers are all fractured in the weld zone near the NiTi side,which is attributed to the enrichment of intermetallic compounds including Fe2Ti and Ni3Ti.The fracture mechanisms of different joints are strongly depen-dent on the types of interlayers,and the joints without interlayer,adding Ni interlayer and adding FeNi interlayer exhibit cleavage fracture,intergranular fracture and mixed fracture composed of cleavage and tearing ridge,respectively.Compared with the brittle laves phase Fe2Ti,Ni3Ti phase can exhibit certain plasticity,block the crack propagation and change the direction of crack propagation.The composite structure of Ni3Ti and Fe2Ti will be formed when the FeNi alloy is taken as the interlayer,which provides the joint excellent mechanical properties,with rupture strength of 343 MPa.
查看更多>>摘要：The plate-shaped θ'(Al2Cu)precipitate acts as one of the primary strengthening phases in Al-Cu alloys.The interface,especially the semicoherent interface,between Al-Cu solid solution(αAl)and θ'phase con-tains a lot of clues about phase transformations.Thus,these interfacial structures in an Al-Cu alloy after high-temperature and longtime aging have been analyzed in detail using atomic-scale high-angle annu-lar dark-field scanning transmission electron microscopy and first-principles calculations in this work.It was found that the lateral growth of θ'precipitates is subjected to a combination of several major mech-anisms under this aging condition.Except for some common intermediate phases,two novel and striking structures were observed on the interface,which implies two alternative atomic diffusion mechanisms for θ'precipitate growth.For one condition,the atomic diffusion from αAl to θ'phase transformation adopts an interstitialcy mechanism based on additional Al atoms.For the other condition,the diffusion is carried out through Al atoms.Both mechanisms are distinctly different from the previous theory based on direct diffusion of Cu atoms.The first-principle calculations also confirm that these newfound diffusion processes are energetically favored.
查看更多>>摘要：Unlike other parts of the body,jaw defection often involves dental and periodontal tissues,which colo-nized a great many oral anaerobic bacteria.As a remarkable degradable material,magnesium has become an excellent candidate for orthopedic appliances recently.But the high degradation rate is still a big prob-lem.Making a biodegradable coating with good biocompatibility to slow down the degeneration rate of magnesium is one of the best methods.However,protective coatings will impair the antibacterial effects of magnesium which is caused by the rise of pH value throughout its degradation.To solve this problem,a series of composite coatings with different amounts of CuO particles(3,5 and 7 wt.％)were fabricated on pure magnesium through plasma electrolytic oxidation(PEO)to investigate in vitro biocompatibility and the antibacterial abilities against Porphyromonas gingivalis(P.gingivalis).Surface characterization and degradation behavior of the copper-bearing PEO coatings were also systematically studied.Furthermore,the most optimum coating was also systematically studied by X-ray photoelectron spectroscopy(XPS)and electrochemical corrosion test.Results of the present research revealed that adding proper amount of CuO into PEO coatings could greatly improve the antibacterial abilities of the PEO coatings.The antibac-terial activities of copper-bearing PEO coatings were excellent and revealed concentration-dependent and time-dependent.Biocompatibility of copper-bearing PEO coatings showed that proper amount of Cu could promote cell proliferation.Compared with other PEO coatings in this study,PEO-7Cu showed some inhibition effects on cell proliferation and adhesion for long-term use.Electrochemical corrosion tests and immersion tests showed that PEO-5Cu and PEO-7Cu copper-bearing PEO coatings would provide satisfying corrosion resistance effects,while PEO-3Cu was poorer than PEO coatings without Cu.How-ever,compared with uncoated pure magnesium,the corrosion resistance of the PEO coating was much better.Based on the results of antibacterial ability,biocompatibility,and corrosion resistance of the above copper-bearing PEO coatings,PEO-5Cu in this research was recommended to be used in patients with jaw defects.
查看更多>>摘要：The advancement in material science and engineering technology has led to the development of antifoul-ing(AF)coatings which are cheaper,durable,less toxic,and safe to the environment.The use of AF coatings containing tributyltin compounds was prohibited at the beginning of 2003,this necessitated the devel-opment of environmentally friendly coatings.The fouling release coating(FRC)lacks biocides and has low surface energy,low elastic modulus with smooth surface properties,hence a better release effect to fouling organisms.Several functional coatings have been recently developed based on fouling release(FR)technology to combat the effects of biofouling.Here,we provide a brief overview of innovative technologies and recent developments based on FRCs,including silicone,modified fluorinated polymer,cross-linked coatings,amphiphilic copolymer coating,hydrogel coatings,and biomimetic coatings.We also highlight the key issues and shortcomings of innovative technologies based on FRCs.This may give new insights into the future development of marine AF coatings.
查看更多>>摘要：The effect of ultrasonic surface rolling process(USRP)as a severe plastic deformation technology was investigated on the evolution of microstructure,residual stress and surface morphology of TB8 alloys with body-centered cubic structure.Stress-controlled rotating-bending fatigue tests indicated increased fatigue strength in USRP samples prepared using different number of passes compared to the base mate-rial,which was attributed to the presence of gradient structure surface layers.Five subsequent USRP passes resulted in the highest fatigue strength,due to the optimal surface properties including higher extent of grain refinement,larger compressive residual stresses,"smoother"surface morphology and increased micro-hardness.However,the effect of USRP technology on improving fatigue strength of TB8 alloy was not significant in comparison with that of other titanium alloys(for example,Ti6Al4V),which was attributed to the notable surface residual stresses relaxation revealed from measurements on post-fatigued USRP samples.Electron backscatter diffraction analysis confirmed that fatigue crack initiation occurred in the larger grains on the surface with high Schmid factor.Small cracks were found to propa-gate into the core material in a mixed transgranular and intergranular mode.Further analysis indicated that grain growth existed in post-fatigued USRP-treated TB8 samples and that the average geometrically necessary dislocations value reduced after fatigue loading.
查看更多>>摘要：Developing an electrically conductive and corrosion-resistant coating is essential for metal bipolar plates of polymer electrolyte membrane fuel cells(PEMFCs).Although enhanced corrosion resistance was seen for Cr coated stainless steel(Cr/SS)bipolar plates,they experience a quick decrease of through-plane electrical conductivity due to the formation of a porous and low-conductive corrosion product layer at the plate surface,thus leading to an increase in interfacial contact resistance(ICR).To tackle this issue,the multilayer Cr coatings were deposited using the magnetron sputtering with a remote inductively coupled oxygen plasma(O-ICP)in the present study.After the O-ICP treatment,a Cr oxide layer(CrO*)is formed on the specimen surface.The CrO*/Cr/SS has a remarkably lower stable corrosion rate(iss)than that of the native Cr oxides(CrOn/Cr/SS).Compared with CrOn/Cr/SS,the excellent performance of CrO*/Cr/SS is attributed to a denser and thicker surface layer of CrO* with Cr being oxidized to its highest valence state,Cr(Ⅵ).More importantly,the through-plane electrical conductivity of the specimens treated by the opti-mized O-ICP decreases much slowly than CrOn/Cr/SS and thus,the increament of ICR of CrO*/Cr/SS after the potentiostatic polarization test is considerably smaller than that of CrOn/Cr/SS,which is benefited from the reduced iss that mitigates the deposition of corrosion products and hinders further oxidation of Cr coating.Therefore,CrO*/Cr/SS proves to be a well balanced trade-off between corrosion resistance and through-plane electrical conductivity.The results of this study demonstrate that O-ICP treatment on a conductive metal coating is an effective strategy to improve the corrosion resistance and suppress the increase of ICR over the long-term polarization.The technique reported herein exhibits its promis-ing potential application in preparing corrosion resistant and electrically conductive coatings on metal bipolar plates to be used in PEMFCs.
查看更多>>摘要：Efficient collection of water from fog provides a potential solution to solve the global freshwater shortage problem,particularly in the desert or arid regions.In this work,a flexible and highly efficient fog collector was prepared by mimicking the back exoskeleton structure of the Namib desert beetle.The improved fog collector was constructed by a superhydrophobic-superhydrophilic patterned fabric via a simple weaving method,followed by in-situ deposition of copper particles.Compared with the conventional fog collector with a plane structure,the fabric has shown a higher water-harvesting rate at 1432.7 mg/h/cm2,owing to the biomimetic three-dimensional structure,its enhanced condensation performance enabled by the copper coating and the rational distribution of wetting units.The device construction makes use of the widely available textile materials through mature manufacturing technology,which makes it highly suitable for large-scale industrial production.
查看更多>>摘要：Graphite flake/Cu composite has attracted tremendous attention as a promising heat sinks materi-als owing to its easy machinability and superior thermal properties.However,its preparation process still faces several technological limitations including complex,time-consuming and costly synthetic approaches.In this work,a facile and scalable intermittently electroplated method is applied to pre-pare Cu-coated graphite flake composite powders,which are subsequently sintered into dense composite bulks.The results show that the graphite flake is successfully coated with a uniform and compact Cu shell,which effectively inhibits the segregation accumulation of graphite flakes and contributes to homoge-neous distribution of graphite in the sintered graphite flake/Cu composites.The as-sintered composites exhibit an excellent thermal conductivity of 710W·m-1·K-1 and an outstanding bending strength of 93 MPa.Such performance,together with the simple,efficient powder-preparation process,suggests that the present strategy may open up opportunities for the development of thermal management materials.
查看更多>>摘要：Alloys with large solidification intervals are prone to issues from the disordered growth and defect for-mation;accordingly,finding ways to effectively optimize the microstructure,further to improve the mechanical properties is of great importance.To this end,we couple travelling magnetic fields with sequential solidification to continuously regulate the mushy zones of Al-Cu-based alloys with large solid-ification intervals.Moreover,we combine experiments with simulations to comprehensively analyze the mechanisms on the optimization of microstructure and properties.Our results indicate that only down-ward travelling magnetic fields coupled with sequential solidification can obtain the refined and uniform microstructure,and promote the growth of matrix phase α-Al along the direction of temperature gradient.Additionally,the secondary dendrites and precipitates are reduced,while the solute partition coefficient and solute solid-solubility are raised.Ultimately,downward travelling magnetic fields can increase the ultimate tensile strength,yield strength,elongation and hardness from 196.2 MPa,101.2 MPa,14.5％ and 85.1 kg mm-2 without travelling magnetic fields to 224.1 MPa,114.5 MPa,17.1％ and 102.1 kg mm-2,and improve the ductility of alloys.However,upward travelling magnetic fields have the adverse effects on microstructural evolution,and lead to a reduction in the performance and ductility.Our findings demonstrate that long-range directional circular flows generated by travelling magnetic fields direction-ally alter the transformation and redistribution of solutes and temperature,which finally influences the solidification behavior and performance.Overall,our research present not only an innovative method to optimize the microstructures and mechanical properties for alloys with large solidification intervals,but also a detailed mechanism of travelling magnetic fields on this optimization during the sequential solidification.
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