查看更多>>摘要：Welded structures in aero-engines commonly operate in high-temperature environments,making them susceptible to reduced fatigue life and premature failure due to welding defects within the structure.Thus,the gigacycle fatigue behaviors of titanium alloy welded joints at both room temperature(RT)and 400 ℃ were investigated,aiming to uncover the mechanism behind the formation of fine granular area(FGA)surrounding welded pores.The research findings demonstrate that the S-N curves of TC17 tita-nium alloy electron beam welded joint undergo a transition from a single linear decline at RT to a bilin-ear decline at 400 ℃.However,the fatigue failure mode remains unaffected by temperatures,and crack initiation is attributed to welded pores.By utilizing the Chapetti model curve to modify the Kitagawa-Takahashi(K-T)diagram,the lower threshold stress amplitude is introduced,enabling the determination of a safe size for welded pores at 400 ℃,which is calculated to be 11.3 μm.Additionally,the Gumbel probability distribution function is employed to assess the maximum size of welded pores.Finally,based on dislocation interactions,the formation mechanism of the FGA consisting of discontinuous nanograins with high-density dislocations is elucidated.
查看更多>>摘要：The construction of one-dimensional(1D)sulfides has attracted extensive attention for improving mi-crowave absorption(MA)performance owing to the anisotropic conductive networks.However,the syn-thesis of conductive 1D hierarchical materials with unique interfacial polarization and excellent MA prop-erties remains challenging.In this study,cable-like MoS2/Ni3S2 was synthesized by a one-step hydrother-mal strategy.The complex permittivity of the binary composites could be improved by tuning the thick-ness of the MoS2 coating.Importantly,the construction of heterogeneous contacts by MoS2 and Ni3S2 contributed to enhanced polarization loss,and the charge distribution was validated by electron holog-raphy.The wide efficient absorption bandwidth can reach above 4.8 GHz at a thin thickness.These new discoveries shed light on novel structures for 1D sulfide materials and the design of functional core-shell composites for microwave absorption.
查看更多>>摘要：A hydrogel dressing based on bacterial cellulose(BC),which is grafted with quaternary ammonium func-tional and crosslinked with the gelatin-heparin system,is prepared to provide the features mainly con-cerning softness,high swelling ratio,antibacterial property,and biocompatibility.An innovation of prepa-ration is that the BC is beaten into short-chain scaffolds to improve the efficiency of grafting,which not only simplifies the preparation process but also avoids the biotoxicity caused by the introduction of toxic catalyst such as dimethyl sulfoxide(DMSO)or uncertain toxic side products in long-chain graft-ing.Scanning electron microscopy(SEM)shows that the QBC/Hep/Gel composite hydrogel possesses a three-dimensional mesh structure with high porosity.The hydrogel shows outstanding water manage-ment performance indicated by the swelling ratio of 1476％,water retention ratio of more than 90％at 120 h,and moisture permeability of 3296 g m-2 24 h-1.The antibacterial experiment is implemented with staphylococcus aureus,and the antibacterial effect is represented by an inhibition zone of 3 cm in diameter.In vivo animal experiments suggested that QBC/Hep/Gel could effectively promote epithelial reconstruction,collagen deposition,and angiogenesis in normal wounds,reduce inflammation,and ac-celerate wound healing.All these results indicate that the proposed QBC/Hep/Gel hydrogel is a potential composite for antibacterial dressing.
查看更多>>摘要：High-temperature titanium alloys are the key materials for the components in aerospace and their service life depends largely on creep deformation-induced failure.However,the prediction of creep rupture life remains a challenge due to the lack of available data with well-characterized target property.Here,we proposed two cross-materials transfer learning(TL)strategies to improve the prediction of creep rupture life of high-temperature titanium alloys.Both strategies effectively utilized the knowledge or information encoded in the large dataset(753 samples)of Fe-base,Ni-base,and Co-base superalloys to enhance the surrogate model for small dataset(88 samples)of high-temperature titanium alloys.The first strategy transferred the parameters of the convolutional neural network while the second strategy fused the two datasets.The performances of the TL models were demonstrated on different test datasets with varying sizes outside the training dataset.Our TL models improved the predictions greatly compared to the mod-els obtained by straightly applying five commonly employed algorithms on high-temperature titanium alloys.This work may stimulate the use of TL-based models to accurately predict the service properties of structural materials where the available data is small and sparse.
查看更多>>摘要：Relationship between precipitation strengthening and creep resistance improvement has been an impor-tant topic for the widespread applications of magnesium alloys.Generally,static precipitation strength-ening through thermal stable precipitates would generate satisfactory creep resistance.However,an op-posite example is presented in this work and we propose that the size of precipitates plays a crucial role in controlling the operative creep mechanisms.In addition,the precipitate components along with their crystal structures in the crept Mg-4Al-3Sm-0.4Mn samples with/without pre-aging were thor-oughly studied using Cs aberration-corrected high-angle annular dark-field scanning transmission elec-tron microscopy(HAADF-STEM).Previous aging generates a large density of fine precipitates(＜～5 nm)homogeneously distributing in Mg matrix and exhibiting satisfactory strengthening effect.However,the number density of precipitate strings consisting of several or even dozens of relatively coarse precipitates(～10 nm)was significantly decreased at the same time.As revealed in this work,the relatively coarse particles in Mg matrix are much more efficient than the fine precipitates in promoting dislocation climb.Therefore,the rate-controlling mechanisms are transferred from dislocation climb to dislocation slip after previous aging,thus leading to degradation of creep resistance.Moreover,there are mainly five types of precipitates/clusters,namelyβ"-(Al,Mg)3Sm,Al5Sm3,ordered Al-Sm cluster,ordered Al-Mn cluster and ordered/unordered AlMnSm clusters.The crystal structures of the former two precipitates were discussed and the formation mechanisms of the precipitates/clusters were revealed.
查看更多>>摘要：In this work,selective laser melting(SLM)process is used to prepare the AlNi6TiZr alloy.By analyzing the printing quality and mechanical properties of the printed specimens with different process parameters,the SLM forming window of AlNi6TiZr is obtained.The relative density of the sample printed with 270 W-1100 mm/s(laser energy density:82 J/mm3)reaches 99.7％,exhibiting excellent mechanical properties(yield strength(YS):421.7 MPa;ultimate tensile strength(UTS):480.4 MPa).After an aging treatment of 325 ℃-12 h,the YS and UTS of the sample increased to 494 MPa and 550.7 MPa,respectively.Adding Ni,Ti,and Zr components promoted the generation of multi-phase precipitates in the Al alloy and improved the synergistic strengthening effect of multi-phases.The hard-shell structure(HSS)formed by the Al3Ni phase at the grain boundary significantly strengthened the grain boundary strength.The precipitated Al3(Ti,Zr)phases at the grain boundaries prevent grain growth and dislocation movement.The Al3Ni and Al3(Ti,Zr)phases have good thermal stability that can still maintain excellent enhancement effects at high temperature.AlNi6TiZr alloy has great application prospects in medium and high-temperature environments.
查看更多>>摘要：Ferromagnetic bulk metallic glasses(FBMGs)possess excellent soft magnetic properties,good corrosion resistance,and high strength.Unfortunately,their commercial utility is limited by their brittleness.In this work,we report the enhancement in the room-temperature plasticity during the compression(25％)and bending flexibility of Fe74Mo6P13C7 FBMG by using water quenching.The high-energy synchrotron X-ray measurements,high-resolution transmission electron microscopy,three-dimensional X-ray microtomog-raphy,and finite element simulation were performed to reveal the origin.It was found that the M-shape profile of residual stress improves the mechanical properties of FBMGs,particularly their plasticity.The reversal of the heat-transfer coefficient and cooling rate from the'vapor blanket'to'nucleate boiling'transition during water quenching processing is the main cause of the unusual profile of residual stress in glassy cylinders.Encouraged by the progress in developing flexible silicate glasses,this work highlights a processing method to improve plasticity and surmount technical barriers for the commercialization of FBMGs.
查看更多>>摘要：The microstructural factors contributing to the high strength of additive-manufactured Al-Si alloys us-ing laser-beam powder bed fusion(PBF-LB)were identified by in-situ synchrotron X-ray diffraction in tensile deformation and transmission electron microscopy.PBF-LB and heat treatment were employed to manufacture Al-12％Si binary alloy specimens with different microstructures.At an early stage of de-formation prior to macroscopic yielding,stress was dominantly partitioned into the α-Al matrix,rather than the Si phase in all specimens.Highly concentrated Si solute(～3％)in the α-Al matrix promoted the dynamic precipitation of nanoscale Si phase during loading,thereby increasing the yield strength.After macroscopic yielding,the partitioned stress in the Si phase monotonically increased in the strain-hardening regime with an increase in the dislocation density in the α-Al matrix.At a later stage of strain hardening,the flow curves of the partitioned stress in the Si phase yielded stress relaxation owing to plastic deformation.Therefore,Si-phase particles localized along the cell walls in the cellular-solidified microstructure play a significant role in dislocation obstacles for strain hardening.Compared with the results of the heat-treated specimens with different microstructural factors,the dominant strengthening factors of PBF-LB manufactured Al-Si alloys were discussed.
查看更多>>摘要：MgH2,as one of the typical solid-state hydrogen storage materials,has attracted extensive attention.However,the slow kinetics and poor cycle stability limit its application.In this work,LiBH4 and YNi5 alloy were co-added as additives to MgH2 via ball milling,thereby realizing an excellent dehydrogenation per-formance and good cycle stability at 300 ℃.The MgH2-0.04LiBH4-0.01YNi5 composite can release 7 wt.％of hydrogen in around 10 min at 300 ℃ and still have a reversible hydrogen storage capacity of 6.42 wt.％after 110 cycles,with a capacity retention rate as high as 90.3％based on the second dehydrogenation capacity.The FTIR results show that LiBH4 can reversibly absorb and desorb hydrogen throughout the hydrogen ab/desorption process,which contributes a portion of the reversible hydrogen storage capacity to the MgH2-0.04LiBH4-0.01YNi5 composite.Due to the small amount of LiBH4 and YNi5,the dehydro-genation activation energy of MgH2 did not decrease significantly,nor did the dehydrogenation enthalpy(△H)change.However,the MgNi3B2 and in-situ formed YH3 during the hydrogen absorption/desorption cycles is not only beneficial to the improvement of the kinetics performance for MgH2 but also improves its cycle stability.This work provides a straightforward method for developing high reversible hydrogen capacity on Mg-based hydrogen storage materials with moderate kinetic performance.
查看更多>>摘要：The demand for the swirl nozzle with enhanced temperature resistance and lightweight properties is in-creasing as the thrust-to-weight ratio of aero-engines rises.The Al2O3 ceramic swirl nozzle can maintain high strength in a hostile environment of high temperature and severe corrosion,while also meeting the requirements of aircraft to enhance efficiency and decrease weight.However,Al2O3 ceramics are limited in their application for aerospace components due to their poor thermal shock resistance(TSR)stemming from their inherent brittleness.This work reported an innovative design and fabrication strategy based on photopolymerization 3D printing technology to realize the three-dimensional shell structure through element interdiffusion and nanoscale stacking of the reinforced phase.With this strategy,a novel type of the new dual-structure Al2O3 ceramic composed of MgAl2O4 shell structure and matrix could be con-structed in situ.The nano-sized MgAl2O4 caused a crack passivation effect after the thermal shock,which could improve the strength and TSR of 3D-printed Al2O3 ceramic.In addition,the effects of MgO content and sintering temperature on sintering behavior,flexural strength,porosity,and TSR of Al2O3 ceram-ics manufactured by digital light processing(DLP)processing were systematically studied.The optimum overall performance of Al2O3 ceramics was obtained at the sintering temperature of 1550 ℃ and the MgO content of 1.0 wt.％,with a maximum flexural strength of 111.929 MPa and a critical temperature difference of 374.24 ℃ for TSR.Based on the above research,an aero-engine swirl nozzle with high ther-mal shock resistance has been successfully prepared by ceramic 3D printing technology,which enhances high-temperature resistance and promotes lightweight design in aero-engine.
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