查看更多>>摘要：The synergistic effect of Mo and Zr additions on microstructure evolution,room-temperature fracture toughness and microhardness of Nb-22Ti-15Si-xMo-yZr(x=4,8,y=3,6)alloys manufactured by laser directed energy deposited(L-DED)have been investigated.The major phases in as-deposited 4Mo-3Zr alloy are Nb solid solution(Nbss),Nb3Si and y-Nb5Si3.The Nb3Si phases disappear with increasing Mo content to 8 at.％or increasing Zr content to 6％.γ-Nb5Si3 precipitates formed in the Nbss of as-deposited xMo-yZr alloys due to the cyclic re-heating,and the γ-Nb5Si3 precipitates and Nbss matrix exhibits ori-entation relationship(OR)of[001]Nbss//[1112]γ and(110)Nbss//(01(1)0)γ in as-deposited 4Mo-6Zr alloy.The microstructure of xMo-yZr alloys became relative homogeneity and the Nbss matrix showed the better continuity after the heat treatment(1400℃/30 h).The Nb3Si phase has transformed into Nbss and α-Nb5Si3 with the OR have been determined as{100}Nbss//{100}α and{111}Nbss//{111}α in the heat-treated 4Mo-3Zr alloy.When Mo content increase to 8at.％,a part of γ-Nb5Si3 phase also transformed into theα-Nb5Si3 phase with the OR have been determined as{11(2)0}y//{110}α and{10(1)0}y//{111}α after heat treatment.Among the as-deposited alloys,the 4Mo-6Zr alloy has the highest fracture toughness KQ with the lowest hardness.The average KQ of 4Mo-6Zr and 8Mo-6Zr alloys increased by 28％and 30％after the heat treatment,and reached 13.61 and 11.43 MPa·m1/2,respectively.The hardness of Nb-22Ti-15Si-xMo-yZr alloys is significantly decreased after the heat treatment.
查看更多>>摘要：Nowadays,carbon frameworks derived from natural biomaterials have attracted extensive attention for electromagnetic interference(EMI)shielding due to their renewability and affordability.However,it is critical and challenging to achieve effective regulation of shielding effectiveness(SE)as well as weaken the strong EM reflection of highly conductive biomass-based carbon materials.Herein,commercial cotton pads with oriented structure were selected as carbonaceous precursor to fabricate aligned carbon net-works by pyrolysis,and the EMI SE of the samples with increased temperature of 800-1000℃can be accurately controlled in the effective range of～21.7-29.1,～27.7-37.1 and～32.7-43.3 dB with high reflec-tion coefficient of＞0.8 by changing the cross-angle between the electric-field direction of incident EM waves and the fiber-orientation direction due to the occurrence of opposite internal electric field.More-over,the further construction of Salisbury absorber-liked double-layer structure could result in an ultra-low reflection coefficient of only～0.06 but enhanced SE variation range up to～38.7-49.3 dB during the adjustment of cross-angle,possibly due to the destructive interference of EM waves in the double-layer carbon networks.This work would provide a simple and effective way for constructing high-performance biomass carbon materials with adjustable EMI shielding and ultra-low reflectivity.
查看更多>>摘要：The dominant hydride precipitates have been well demonstrated to follow two types of orienta-tion relationships(ORs)with Ti matrix:OR1 with{0001}//{001},<1(2)10>//<110>and OR2 with{0001}//{1(1)1),<1(2)10>//<110>.Within the grains with special orientations,the complicated inter-actions of different hydride variants inside Ti-hydride diffusion layer are characterized in this work.For OR1 hydride layer,the orientations of{10(1)0}plane parallel to the sample surface and a-axis parallel to the normal direction prefer multiple OR1 variants.The orientations favorable for OR2 hydride layer are:{10(1)3}plane parallel to sample surface corresponding to the layer with one OR2 variant dominated and c-axis parallel to the surface normal with multiple OR2 variant layer preferred.Furthermore,{1012}ex-tension twins and{11(2)2}contraction twins are activated to accommodate the OR2 hydride-induced sur-face expansion and local misfit strain.The stimulation of these two twins is also orientation-dependent:{1012}and{1122}twins are observed in the grains with c-axis parallel to and deviated from the sur-face normal,respectively.The further variant selection for each twin mode is performed through shear accommodation of hydride-twin pairs.
查看更多>>摘要：Fe-based metallic glasses(MGs)have shown great commercial values due to their excellent soft magnetic properties.Magnetism prediction with consideration of glass forming ability(GFA)is of great signifi-cance for developing novel functional Fe-based MGs.However,theories or models established based on condensed matter physics exhibit limited accuracy and some exceptions.In this work,based on 618 Fe-based MGs samples collected from published works,machine learning(ML)models were well trained to predict saturated magnetization(Bs)of Fe-based MGs.GFA was treated as a feature using the experimen-tal data of the supercooled liquid region(ΔTx).Three ML algorithms,namely eXtreme gradient boosting(XGBoost),artificial neural networks(ANN)and random forest(RF),were studied.Through feature selec-tion and hyperparameter tuning,XGBoost showed the best predictive performance on the randomly split test dataset with determination coefficient(R2)of 0.942,mean absolute percent error(MAPE)of 5.563％,and root mean squared error(RMSE)of 0.078 T.A variety of feature importance rankings derived by XGBoost models showed that ΔTx played an important role in the predictive performance of the models.This work showed the proposed ML method can simultaneously aggregate GFA and other features in ther-modynamics,kinetics and structures to predict the magnetic properties of Fe-based MGs with excellent accuracy.
Dina BayoumyKwangsik KwakTorben BollStefan Dietrich...
121-133页
查看更多>>摘要：The Al-Mn-Sc-based alloys specific for additive manufacturing(AM)have been recently developed and can reach ultrahigh strength and adequate elongation.However,these alloys commonly exhibit non-uniform plasticity during tensile deformation,which is a critical issue hindering their wider application.In this work,the origin of this non-uniform plasticity of the alloys produced by laser powder bed fusion(LPBF)has been systematically investigated for the first time.The results show that the loss of uniform plasticity in the alloy originates from microstructural regions containing equiaxed fine-grains(FGs)(～650 nm in size)at the bottom of the melt pools.In micro-tensile tests,the strength of these FG regions can reach a peak of～630 MPa.After this,an apparent yield drop occurs,followed by rapid strain softening.This FG behavior is associated with intermetallic particles along grain boundaries and a lack of uniform mobile dislocations during deformation.The columnar coarse-grain(CG)regions in the remaining melt pools show uniform plasticity and moderate work hardening.Furthermore,the quantitative calculations indicate that the solid solution strengthening in these two regions is similar.Nevertheless,secondary Al3Sc precipitates contribute to～260 MPa strength in the FG,compared to 310 MPa in the CG due to their different number density.In addition,grain boundary strengthening can reach 230 MPa in the FG region;nearly double the CG region value.
Daniel González-Mu?ozAlmudena Gómez-AvilésCarmen B.MolinaJorge Bedia...
134-143页
查看更多>>摘要：The application of organic photocatalysts towards the oxidation of pollutants in water is hampered by dif-ferent limitations such as their insolubility in the media.Herein,we report that the grafting of a photo-organocatalyst into mesoporous silica materials is an ideal approach to obtain effective catalysts.Thereby,the photocatalyst 10-phenylphenothiazine(PTH)was easily anchored into three different mesoporous silica-based materials(MSN,MSU-2 and SBA-15)with different particle sizes and pore sizes through an amide bond formation.The materials were characterized using IR analysis,solid-state X-ray diffraction,porosity and microscopy(SEM and TEM)techniques,showing that PTH is immobilized inside the pores of the materials and its optical properties are maintained after the anchoring.Although homogeneous PTH was inactive in water media,the three photocatalytic materials were active for the degradation of pollutants.SBA-15-AP-PTH exhibited the highest catalytic performance towards the degradation of ac-etaminophen and diclofenac under solar irradiation,finding in this manner a new strategy for the decon-tamination of pollutants.
查看更多>>摘要：Pd40Ni40P20(at.％)samples with different enthalpy states were fabricated through high-pressure torsion or sub-Tg annealing of the as-cast material.Subsequently,the underlying structural relaxation was stud-ied by in-situ shear modulus measurements and modulated differential scanning calorimetry.The results show that high-pressure torsion leads to shear modulus softening and an increase of the nonreversible exothermic enthalpy,indicating a significant structural rejuvenation,while sub-Tg annealing causes shear modulus hardening and a decrease of the nonreversible exothermic enthalpy.The reversible endothermic effect which can reflect the fractional change of supercooled liquid with temperature was found to be almost identical for all samples,and independent of deformation or thermal history.The total heat flow can be well correlated with the shear modulus within the framework of interstitialcy theory.Further-more,we demonstrate that the structural relaxation below Tg decouples into internal stress relaxation and β-relaxation.In addition,this work indicates that the processes of α-relaxation and β-relaxation in the metallic glass are of similar structural origin but occur on different spatial scales.
查看更多>>摘要：The fabrication of high-performance electromagnetic(EM)wave absorption(EMA)materials is an effec-tive strategy to deal with ever-increasing EM pollution.In this work,a series of manganese oxides/porous carbon(MnxOy@C)hybrid composites are obtained by a two-step process.It is revealed that different manganese oxides play various influence on the dielectric properties of absorbers.Owing to the moder-ate complex permittivity of MnO@C hybrid composites,the optimal reflection loss could reach as high as-76.0 dB at the matching thickness of 2.0 mm with 5.2 GHz of effective absorption bandwidth at thick-ness of 2.1 mm.We demonstrated that the addition of porous carbon is vital for enhancing EMA perfor-mance of composites,which not only coordinates impedance matching allowing more EM waves enter the absorber,but also provides the path for electron movement,thus profiting conductive loss.Besides,different heterogeneous interfaces including porous carbon,manganese oxide and so on,are conducive to contribution of interface polarization.The most noteworthy is ingenious design of composite materials and systematic research of EM energy attenuation mechanism in this work will provide the possibility to realize high-performance EMA.
查看更多>>摘要：Magnetocaloric materials undergoing reversible phase transitions are highly desirable for magnetic refrig-eration applications.(Mn,Fe)2(P,Si)alloys exhibit a giant magnetocaloric effect accompanied by a magne-toelastic transition,while the noticeable irreversibility causes drastic degradation of the magnetocaloric properties during consecutive cooling cycles.In the present work,we performed a comprehensive study on the magnetoelastic transition of the(Mn,Fe)2(P,Si)alloys by high-resolution transmission electron mi-croscopy,in situ field-and temperature-dependent neutron powder diffraction as well as density func-tional theory calculations(DFT).We found a generalized relationship between the thermal hysteresis and the transition-induced elastic strain energy for the(Mn,Fe)2(P,Si)family.The thermal hysteresis was greatly reduced from 11 to 1 K by a mere 4 at.％substitution of Fe by Mo in the Mn1.15Fe0.80P0.45Si0.55 alloy.This reduction is found to be due to a strong reduction in the transition-induced elastic strain energy.The significantly enhanced reversibility of the magnetoelastic transition leads to a remarkable improvement of the reversible magnetocaloric properties,compared to the parent alloy.Based on the DFT calculations and the neutron diffraction experiments,we also elucidated the underlying mechanism of the tunable transition temperature for the(Mn,Fe)2(P,Si)family,which can essentially be attributed to the strong competition between the covalent bonding and the ferromagnetic exchange coupling.The present work provides not only a new strategy to improve the reversibility of a first-order magnetic transition but also essential insight into the electron-spin-lattice coupling in giant magnetocaloric materials.
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