查看更多>>摘要：Heterogeneous coarse surface crystallites induced in the industrial Fe-rich nanocrystalline alloy is an ob-stacle for high-frequency and high-power commercial applications.Herein,the phase,crystal orientation,nanostructure and magnetic domain evolution of the surface-crystallized Fe-rich alloy were systematically investigated.Microstructure and inverse pole figures analysis confirms that the DO3 ordered dendritic-crystallites bear<001>-oriented fiber texture before and after annealing at the free surface,while ultra-fine nanocrystals are randomly oriented in the interior and wheel surface after annealing.As compared to zero magnetic-field-annealing,the transverse magnetic-field-annealing induces weakly oriented fiber texture and relatively uniform dendritic-crystallites at the surface,and uniform anisotropy in the inte-rior and surface,which promotes smooth wall motion at the surface and magnetization rotation in the interior.This synergetic effect reduces the excess loss and leads reduction in dynamic loss at 1.0 T and 10 kHz by 36％.
查看更多>>摘要：Influence of Zr contents on high-temperature magnetic performance of Sm(CobalFe0.09Cu0.09Zrx)7.2(x = 0.025,0.03,0.035,0.04)magnets were investigated.As x increases from 0.025 to 0.04,the tem-perature coefficient of intrinsic coercivity(Hcj)is optimized from-0.1673％K-1 to-0.1382％K-1 and the Hcj at 773 K gradually increases from 556.32 kA m-1 to 667 kA m-1.The microstructure and microchem-istry of different Zr-content magnets were revealed by a transmission electron microscope equipped with EDS.The increasing Zr content induces that the average size of cells decreases from～76 nm to～56 nm and the weight fraction of 1:5H cell boundary phase increases from～25％to～37％as well,resulting decreasing of the average Cu content at cell boundaries from 13.59 at％to～8.52 at％.It is found that the Cu-lean characteristic at cell boundary phase is the reason that gives rise to higher magnetic properties at elevated temperatures for x = 0.04 magnet.
查看更多>>摘要：The retrogression and re-aging(RRA)processes,aimed mainly at tailoring intergranular precipitates,could significantly improve the corrosion resistance(i.e.,stress corrosion cracking resistance)without considerably decreasing the strength,which signifies that an efficient control of the size,distribution and evolution of intergranular and intragranular precipitates becomes critical for the integrated prop-erties of the(mid-)thick high-strength Al alloy plates.Compared to RRA process with retrogression at 200℃(T77),this study investigated the impact of a modified RRA process(MT77)with lower ret-rogression temperatures(155-175℃)and first-stage under-aging on the properties of a high-strength AA7050 Al alloy,in combination with detailed precipitate characterization.The study showed that the strength/microhardness of the RRA-treated alloys decreased with raising retrogression temperature and/or prolonging retrogression time,along with the increased electrical conductivity.The rapid responsiveness of microstructure/property typical of retrogression at 200℃was obviously postponed or decreased by using MT77 process with longer retrogression time that was more suitable for treating the(mid-)thick plates.On the other hand,higher retrogression temperature facilitated more intragranular η precipitates,coarse intergranular precipitates and wide precipitate free zones,which prominently increased the elec-trical conductivity alongside a considerable strength loss as compared to the MT77-treated alloys.With the preferred MT77 process,the high strength approaching T6 level as well as good corrosion resistance was achieved.However,though a relatively homogeneous through-thickness strength was obtained,some small discrepancies of properties between the central and surface areas of an 86-mm thick 7050 Al alloy plate were observed,possibly related to the quenching sensitivity.The precipitate evolution and mech-anistic connection to the properties were discussed and reviewed for high-strength Al alloys along with suggestions for further RRA optimization.
查看更多>>摘要：The proton-irradiated 308L stainless steel weld metal was strained by using constant extension rate ten-sile testing in simulated PWR primary water,and its deformation microstructures and irradiation assisted stress corrosion cracking(IASCC)behavior were investigated.The results suggest that the irradiation sig-nificantly increases the SCC susceptibility of 308L weld metal and causes various deformation microstruc-tures including lathy faulted planes,dislocation channels and deformation twins in austenite and atomic plane rotation in 8-ferrite.The propagation of intergranular IASCC cracks is closely related to the location of the crack tip.For the crack tip in the specimen matrix interior,localized deformation is likely the key factor responsible for the crack growth.For the crack tip close to the specimen surface,however,local-ized corrosion along the grain boundary rather than the localized deformation appears to dominate the crack propagation.Unlike the intergranular cracks,the IASCC cracks along the δ-ferrite/austenite phase boundary can initiate either by crack initiation at the phase boundary or by crack propagation from the grain boundary.In both cases,the cracked phase boundaries contain a large number of carbides and are severely corroded,but no deformation microstructures are observed,which implies that the localized corrosion may play an important role in the IASCC along the phase boundary.In addition,δ-ferrite can retard the IASCC crack propagation along the grain boundary,which is probably related to the reduction of localized deformation by δ-ferrite.
查看更多>>摘要：Deformation kinking as an uncommon plastic deformation mechanism has been reported in several ma-terials while the relevant microstructure evolution and grain refinement behavior at a large strain remain unclear so far.In this study,the issue was systematically investigated by utilizing cold forging to im-pose severe plastic deformation(SPD)on Ti-11 V metastable β-Ti alloys.It is found that the formation of kink bands experiences dislocation gliding,pre-kinking and the ripening of pre-kinks in sequences.The kink bands are subsequently thickened through the coalescence of multiple kink bands in a manner of high accommodation.Ordinary dislocation slip is developed as a dominant deformation mechanism when deformation kinking is exhausted.The resulting grain refinement involves transverse breakdown and lon-gitudinal splitting of dislocation walls and cells,which fragment kink bands into small β-blocks.Further refinement of the β-blocks is still governed by dislocation activities,and finally nanograins with a diam-eter of～15 nm are produced at a large strain of 1.2.Alternatively,it is revealed that nanocrystallization is highly localized inside kink bands while the outer microstructure maintains original coarse structures.Such localized refinement characterization is ascribed to the intrinsic soft nature of kink bands,shown as low hardness in nanoindentation testing.The intrinsic softening of kink bands is uncovered to originate from the inner degraded dislocation density evidenced by both experimental measurement and theoreti-cal calculation.These findings enrich fundamental understanding of deformation kinking,and shed some light on exploring the deformation accommodation mechanisms for metal materials at large strains.
查看更多>>摘要：An AlSiY coating and two MCrAlY+AlSiY composite coatings with different thickness of MCrAlY inter-layer were prepared by arc ion plating(AIP)and vacuum annealing.The isothermal oxidation behavior of coatings at 1100℃for 300 h was also investigated to characterize the microstructure evolution of coat-ings during annealing.The composite coatings exhibited a better high-temperature oxidation resistance at 1100℃.The reason is that the addition of MCrAlY layer can greatly contribute to prevent the diffusion of refractory elements to the outer layer.The inhibition of Al inward diffusion can be much stronger,as the Si content increases in the outer layer during annealing.
查看更多>>摘要：Differential scanning calorimetry(DSC)is a technique extensively applied to analyse precipitation phe-nomena in Al-Mg-Si alloys,yet the processes occurring during non-isothermal DSC heating,in particu-lar the formation of clusters in the early stage and their evolution at higher temperatures,remain ob-scure.Here,we carry out experiments not only to measure heat(via DSC)but also to measure hardness,positron lifetime,electrical resistivity and microstructure of an Al-Mg-Si alloy heated at 3 different rates.Electrical resistivity is measured in situ,the other properties after interrupting the heating process.It is demonstrated that the precipitation process during heating can be divided into various stages,with transition temperatures depending on the heating rate,but the relative behavior of the various measured quantities is connected in the same way.Quenched-in excess vacancies are found to play an important role in cluster formation at lower temperatures,which explains the seeming peculiarity that linear heat-ing at lower temperatures can lead to stronger clustering than isothermal ageing at a higher temperature.These trends are well simulated using a recently developed precipitation model.New aspects about the evolution of these clusters at higher temperatures are revealed by correlating the different measured properties.The methodology applied here could also be extended to investigating more complex non-isothermal heat treatments.
查看更多>>摘要：Herein,a novel strategy was exploited to achieve the delamination of Ti3C2 MXene multilayers into ultra-thin flakes by blossom of Znln2S4 microflowers via a one-pot solvothermal method.There is no need to peel off the MXene bulk ahead of its combination with the semiconductor.The obtained ZnIn2S4/Ti3C2 bi-nary composites were applied for visible-light-driven photocatalytic hydrogen production without noble metal cocatalyst,and the optimized sample exhibited a hydrogen-production efficiency of 978.7 μmol h-1 g-1 with the corresponding apparent quantum efficiency of 24.2％at 420 nm,which was 2.7 times higher than bare ZnIn2S4.Through the comprehensive analysis based on spectroscopy measure-ments,electrochemical techniques and energy band theory,such enhancement was mainly attributed to(1)the highly-exposed surface that was beneficial for the adequate exposure of reactive sites and(2)the intimate contact interface that favored the transfer of photogenerated carriers.This study provides a new way of thinking for synthesizing ultrathin MXene-based composite materials for noble-metal-free and highly-efficient photocatalysis applications.
查看更多>>摘要：The chemical element distributions always strongly affect the deformation mechanisms and mechani-cal properties of alloying materials.However,the detailed atomic origin still remains unknown in high-entropy alloys(HEAs)with a stable random solid solution.Here,considering the effect of elemental fluc-tuation distribution,the deformation behavior and mechanical response of the widely-studied equimolar random CoCrFeMnNi HEA are investigated by atomic simulations combined with machine learning and micro-pillar compression experiments.The elemental anisotropy factor is proposed,and then used to evaluate the chemical element distribution.The experimental and simulation results show that the local variations of chemical compositions exist and play a critical role in the deformation partitioning and me-chanical properties.The high strength and good plasticity of HEAs are obtained via tuning the chemical element distributions,and the optimal elemental anisotropy factor ranges from 2.9 to 3 using machine learning.This trend can be attributed to the cooperative mechanisms depending on the local variational composition:massive partial dislocation multiplication at an initial stage of plastic deformation,and the inhibition of localized shear banding via the nucleation of deformation twinning at a later stage.Using the new insights gained here,it would be possible to create new metallic alloys with superior properties through thermal-mechanical treatment to tailoring the chemical element distribution.
查看更多>>摘要：The effects of Al content and Ca/Al mass ratio on the microstructure and mechanical properties of tung-sten inert gas(TIG)welded Mg-2Ca-xAl-0.5Mn(x=0,1,5)alloy joints were studied in present work.Results showed that increasing Al content was effective in reducing the dendrite spacing at the fusion zone(FZ)edge.The Laves phases in the FZ and the heat-affected zone(HAZ)can be changed from Mg2Ca to(Mg,Al)2Ca with the decrease of Ca/Al ratio,and the(Mg,Al)2Ca could be further transformed to Al2Ca under welding thermal cycle.Furthermore,dynamic dissolution and precipitation of Laves phases and Al8Mn5 phases occurred in the HAZ,resulting in a gradient microstructure and hardness peak in this area.The tensile properties of the joints were significantly improved with the increase of Al content,which was mainly due to the modification of Laves phases.
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