查看更多>>摘要：The composites of Mg20Pr1Sm3Y1Ni10 as-quenched alloy and 3％(mass fraction)M(M=CoS,CoS2,MoS2)catalyst were prepared by high-speed vibration ball mill.The effects of metal sulfides on the hydrogenation and dehydrogenation dynamics of alloys were compared.The results show that the as-milled composites contain a large number of amorphous embedded by a small amount of nanocrystals,and there are many point defects.After ball milling,the crystal grain size in the composites containing CoS is relatively larger,followed by CoS2 and MoS2 a-gain.After hydrogenation,the amorphous phase is crystallized to form Mg2NiH4,YH3,Pr8H1896,Sm3H7,Mg,Co or Mo phases,however,Mg2Ni,YH2,PrH2 and Ni3Y phases appeared after dehydrogenation.The maximum hydrogenation capacity of the composites containing CoS,CoS2 and MoS2 are 3.939％,4.265％and 4.507％(mass fraction),respectively.The hydrogenation saturation ratio of composite containing MoS2 is higher than that of the composites containing CoS and CoS2.The dehydrogenation activation energy of the composites containing CoS,CoS2 and MoS2 is 107.76,68.43 and 63.28 kJ·mol-1 H2.On the improvement of hydrogen storage performance of Mg20Pr1Sm3Y1Ni10 alloy,the catalytic effect of MoS2 sulfide is better than that of CoS2 sulfide,and which is better than CoS sulfide.
查看更多>>摘要：Mg-Y-Zn-Al alloys processed by rapidly solidified ribbon consolidation(RSRC)technique exhibit an exceptional mechanical performance in-dicating promising application potential.This material has a bimodal microstructure consisting of fine recrystallized and coarse nonrecrystallized grains with solute-rich stacking faults forming cluster arranged layers(CALs)and nanoplates(CANaPs),or complete long period stacking or-dered(LPSO)phase.In order to reveal the deformation mechanisms,in-situ synchrotron X-ray diffraction line profile analysis was employed for a detailed study of the dislocation arrangement created during tension in Mg-0.9％Zn-2.05％Y-0.15％Al(atomic percent)alloy.For uncovering the effect of the initial microstructure on the mechanical performance,additional samples were obtained by annealing of the as-consolidated specimen at 300 ℃ and 400 ℃ for 2 h.The heat treatment at 300 ℃ had no significant effect on the initial microstructure,its evolution during tension and,thus,the overall deformation behavior under tensile loading.On the other hand,annealing at 400 ℃ resulted in a significant in-crease of the recrystallized grains fraction and a decrease of the dislocation density,leading to only minor degradation of the mechanical strength.The maximum dislocation density at the failure of the samples corresponding to the plastic strain of 10％-25％was estimated to be about 16 × 1014-20 × 1014 m-2.The diffraction profile analysis indicated that most dislocations formed during tension were of non-basal<a>and pyramidal<c+a>types,what was also in agreement with the Schmid factor values revealed independently from orientation maps.It was also shown that the dislocation-induced Taylor hardening was much lower below the plastic strain of 3％than above this value,which was ex-plained by a model of the interaction between prismatic dislocations and CANaPs/LPSO plates.
查看更多>>摘要：A large-scale fine-grained Mg-Gd-Y-Zn-Zr alloy plate with high strength and ductility was successfully prepared by multi-pass friction stir processing(MFSP)technology in this work.The structure of grains and long period stacking ordered(LPSO)phase were characterized,and the mechanical properties uniformity was investigated.Moreover,a quantitative relationship between the microstructure and tensile yield strength was established.The results showed that the grains in the processed zone(PZ)and interfacial zone(IZ)were refined from 50 to 3 and 4 μm,re-spectively,and numerous original LPSO phases were broken.In IZ,some block-shaped 18R LPSO phases were transformed into needle-like 14H LPSO phases due to stacking faults and the short-range diffusion of solute atoms.The severe shear deformation in the form of kinetic ener-gy caused profuse stacking fault to be generated and move rapidly,greatly increasing the transformation rate of LPSO phase.After MFSP,the ultimate tensile strength,yield strength and elongation to failure of the large-scale plate were 367 MPa,305 MPa and 18.0％respectively.Grain refinement and LPSO phase strengthening were the major strengthening mechanisms for the MFSP sample.In particularly,the strength of IZ was comparable to that of PZ because the strength contribution of the 14H LPSO phase offsets the lack of grain refinement strengthening in IZ.This result opposes the widely accepted notion that IZ is a weak region in MFSP-prepared large-scale fine-grained plate.
Sunghoon ChoiJongwon ShinJoung Sik SuhDongchoul Kim...
2255-2268页
查看更多>>摘要：In this study,a numerical analysis was conducted on the ductile fracture of a 2-mm diameter Mg-1Zn-0.5Mn-0.5Sr-0.1Ca alloy wire during drawing.The hexagonally close-packed crystal structure of Mg alloys causes asymmetric fracture behavior,especially in the compression region.The aim of this study is to develop a comprehensive damage model for Mg alloy wire that accurately predicts ductile fracture,with a focus on the compression region.A novel experimental method was introduced to measure the ductile fracture of Mg alloy wires under different stress states.The wire drawing process was simulated using the generalized incremental stress-state dependent damage(GISSMO)Model and the semi-analytical model for polymers(SAMP)model.The damage model's prediction and the experimental results were found to be in excellent agree-ment,especially in determining crack initiation.Computational analysis established a safe zone diagram for die angle and reduction ratio,and experimental validation confirmed the feasibility of this approach.The proposed damage model can provide a practical and reliable analysis for optimizing the drawing process of Mg alloy wire.
查看更多>>摘要：Biodegradable magnesium(Mg)and its alloys exhibit excellent biocompatibility and mechanical compatibility,demonstrating tremendous po-tential for applications in orthopedics.However,the rapid degradation rate has limited their clinical application.Polycaprolactone(PCL)is com-monly employed as a polymer coating to impede the rapid degradation of Mg.Unfortunately,its long-term anti-corrosion capability and bioac-tivity are inadequate.To address these issues,polydopamine(PDA)-modified zeolitic imidazolate framework-8(PZIF-8)bioactive nanoparticles are fabricated and incorporated into the PCL coating.The PZIF-8 particles,featuring catechol motifs,can enhance the compactness of the PCL coating,reduce its defects,and possess biomineralization ability,thereby effectively improving its anti-corrosive and bioactive properties.Moreo-ver,the active substances released from the degradation of the PZIF-8 particles such as Zn2+and PDA are beneficial for osteogenesis.The corro-sion tests indicate that the corrosion current density of PCL-treated sample decreases by more than one order of magnitude and the amount of H2 released decreases from(023±0.12)to(0.08±0.08)mL·cm-2 after doping with the PZIF-8.Furthermore,the improved corrosion resistance and released PDA and Zn2+from the coating can promote osteogenic differentiation by up-regulating the expression of alkaline phosphatase ac-tivity,related osteogenic genes,and proteins.In addition,in vivo implantation experiments in rabbit femur defects further offer strong evidence that the doping of PZIF-8 nanoparticles accelerates bone reconstruction of the PCL coating.In summary,this work implies a new strategy to fab-ricate a PCL-based coating on Mg-based implants by introducing the PZIF-8 particles for orthopedic applications.
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