查看更多>>摘要：The coarse as-cast lamellar microstructure in TiAl alloys is difficult to be broken completely by thermo-mechanical processing.Some remnant lamellar colonies in the deformed microstructure seriously affect the microstructural homogeneity and deteriorate the properties.In this study,it is found that by isother-mal compression at 1230 ℃ and 1250 ℃,the lamellar colonies of Ti-43.5Al-4Nb-1Mo-0.1B(TNM)alloys can be completely broken.This is attributed to the weakened anisotropic deformation behavior of the lamellar colonies due to the isothermal holding treatment before deformation.The deformation behavior at 1230 ℃ was investigated by quasi-in-situ experiments.It is observed that the regions near lamel-lar colony boundaries first undergo dynamic recrystallization at small strain,while the lamellar colonies gradually break down with increasing strain.The adequate fragmentation of lamellar colonies mainly depends on the recrystallization of α lamellae(αL).The isothermal holding at 1230 ℃ leads to an in-crease in the content and thickness of αL,which allows it to assume more deformation and promotes its recrystallization by reaching critical strain.The interrupted γ lamellae(γL)formed by decomposition during isothermal holding facilitates the occurrence of α recrystallization within the lamellar colonies by hindering dislocation movement.In addition,recrystallized γ grains(γR)are gradually dissolved by the formation of α precipitates inside them through the γ → α phase transformation and the subsequent consumption of α precipitates by the recrystallized α grains.
查看更多>>摘要：Additively manufactured(AM)biodegradable zinc(Zn)alloys constitute an important branch of orthope-dic implants because of their moderate degradation properties and bone-mimicking mechanical proper-ties.In this paper,the microstructural evolution and corrosion mechanisms of zinc-copper(Zn-Cu)alloys prepared by the laser-powder-bed-fusion(L-PBF)additive manufacturing method were investigated.Al-loying with Cu significantly increases the ultimate tensile strength(UTS)of unalloyed Zn,but the UTS and ductility of unalloyed Zn and Zn-2Cu decrease with increasing laser energy density.Unalloyed Zn has a dendritic microstructure,while Zn-2Cu alloy has a peritectic microstructure.The formation of round peri-tectic grains is due to the low-temperature gradient of unalloyed Zn during the AM.The Zn-2Cu samples exhibited higher corrosion rates,addressing the problem of slow degradation of unalloyed Zn.The grain size distribution influences the corrosion behavior of the material.It enhances the corrosion rates of ma-terials with fine grains in a non-passivating environment.However,the 100％extracts of Zn-2Cu samples exhibited greater values of cellular activity compared to unalloyed Zn samples,thus confirming their bet-ter cytocompatibility.This work demonstrates the great potential to design and modulate biodegradable Zn alloys to fulfill clinical needs by using AM technology.
查看更多>>摘要：Hybrid engineering is gradually deemed as a powerful approach to solving the bottleneck problem of metal-organic framework(MOF)derived absorbers for practical application.Herein,a new type of semiconductor/carbon-based hybrid material was successfully prepared by phytic acid(PA)modification and carbonization of MOF/bacterial cellulose(BC)precursors,which remedied the drawbacks of struc-tural instability,lethal byproducts and complicated steps reported previously.Specifically,the obtained Fe(PO3)2@C/phosphorus-doped carbon foam(Fe(PO3)2@C/PCF)had a 3D hybrid micro-nanostructure that integrated spatial microcurrent network,multi-level pores,heterogeneous interfaces and lattice defects,showing its unique advantages of low filler content(15 wt.％),moderate surface reflectivity,multi-band microwave absorption and radar stealth.The experimental analysis and CST simulation further revealed that PA dosage can precisely adjust the hybrid phase content,pore texture and electromagnetic param-eters of the final product to achieve synergistic enhancement of multiple dielectric response,impedance matching and attenuation capacity.As a result,an effective bandwidth(EAB)of 6 GHz and a minimum reflection loss(RLmin)of-57.0 dB were obtained in the Ku-and C-bands,respectively.These encourag-ing results may advance the development of novel MOF-derived absorbents based on the hybridization principle.
查看更多>>摘要：Coherent precipitation of cuboidal γ'-Co3(Al,W)nanoparticles in face-centered-cubic(FCC)-γ matrix is of great significance for improving high-temperature mechanical properties of Co-based superalloys.The present work developed a series of low-density Co-based superalloys in light of the cluster composi-tion formula of[Al1-(Co,Ni)12]((Al0.5(Ti/Nb/Ta)0.5W0.5)(Mo0.5Cr0.5Co0.5)),where the addition of Ti,Nb,and Ta is mixed with an equimolar ratio.It is found that these designed alloys with different combinations of Ti/Nb/Ta,Ti/Nb,and Ti/Ta possess the coherent microstructure of cuboidal γ'nanoprecipitates in the FCC-y matrix.The microstructural evolution of coherent γ/γ'during aging at 1173 K shows that these superalloys exhibit higher thermal stability at high temperatures.Even after aging for 1000 h,there do not exist any other precipitated phases on grain boundaries,except the coarse γ'precipitates.Also,the coarsening rate constants of cuboidal γ'nanoprecipitates in these alloys are very low(K=5.76-6.03 nm3/s),which is mainly ascribed to a moderate lattice misfit(ε=0.28％-0.45％)between γ and γ'.The stable γ/γ'microstructure renders the alloys with prominent mechanical properties,as evidenced by the high yield strength of σYS=438-445 MPa at 1143 K.A large amount of stacking faults appear after compressive deformation and Lomer-Contrell dislocation locks are also formed due to the reaction of partial dislocations of stacking faults.Moreover,the microhardness(285-320 HV)in each alloy keeps almost constant with the aging time.Besides,these superalloys have a relatively lower density(8.67-8.89 g/cm3),among which the alloy containing Ti0.25Ta0.25 also exhibits a much higher γ'solvus temper-ature(1361±2 K)than those of the existing Co-Al-W-based superalloys.
查看更多>>摘要：The interface of ceramic particles and metal matrixes extremely impacts the mechanical properties of particle-reinforced metal matrix composites,especially at elevated temperatures.We provide a strat-egy for constructing extremely fine,in situ-formed coherent nanolamellar solute-twining architectures in a supersaturated MAX/Ni composite to modify the interface,aiming for higher strengths.Through this unique architecture,a coherent interface of ceramic particles and a metal matrix is formed,with an enormous coherent interface known as a ladder interface.The tensile strength at 1023 K is approxi-mately 1 GPa by forming a thermally stable Schwarz crystal structure(＜3 nm).Developing heat-tolerant composites using this architecture may enhance the materials'available properties for high-temperature applications.
查看更多>>摘要：The actual performance of vanadium redox flow batteries(VRFBs)is still significantly constrained by the slow kinetics and major parasitic reactivity of anode issues.Herein,a B-site management strategy of SrBO3(B=Ti,Zr,Hf)perovskites was proposed to promote the anode reaction jointly explored by ex-periments and first-principle calculations.As the atomic number of B increases,the enhanced polarity of the B-O bond and the increased oxygen defect can boost the adsorption of vanadium ions,while the weakened orbital hybridization of the B-O bond facilitates the charge transfer of anode reaction.Com-pared with SrTiO3 and SrZrO3,oversized particles and deformed crystals of SrHfO3 reduce its catalysis.Of SrBO3 perovskites,SrZrO3 stands out in catalysis,owing to its outstanding combination of high hy-drophilicity,large surface area,and desired crystal structure.Further,the VRFB using SrZrO3 presents a superior energy efficiency(EE)of 63.2％at 300 mA cm-2 and an increase of 15％in EE compared with the pristine cell at 200 mA cm-2.This work lays the foundation for building the connections between the structural and compositional flexibility and the tunable perovskite properties desirable for vanadium redox reactions.
查看更多>>摘要：Niobium alloys have found extensive application in industries,such as aerospace,nuclear reactor,and emerging electronic technologies,owing to their high melting point,low density,and remarkable forma-bility.Nevertheless,they still fall short in terms of comprehensive strength,toughness,and thermal stability when subjected to complex impacts and/or torsional forces during service.Here,a dual-phase(BCC/FCC)Nb alloy with attractive mechanical properties and thermal stability was designed by tuning stable element C in the Nb-BCC matrix assisted by hot deformation and aging processes.Our findings reveal that the formation of discontinuous carbides at the grain boundary promotes the phase trans-formation of the matrix from BCC to FCC(K-S orientation relationship),resulting in the formation of FCC thin layers and nano particles.This unique configuration hinders the slipping of dislocations during deformation and impedes the degeneration of microstructures during the thermal cycling process from 200 ℃ to 900 ℃.Moreover,the discontinuous carbides at GBs provide channels to transfer dislocations between various phases and/or grains,which results in attractive mechanical properties and thermal sta-bility.The ultimate tensile strength,yield strength,elongation,and elasticity modulus of the designed Nb alloy reach impressive values of 790.5 MPa,436.5 MPa,39.1％,and 63.5 MPa,respectively.These obser-vations provide guidelines for designing dual-phase Nb alloys with remarkable strength,toughness,and thermal stability for aerospace applications by tuning the stabilizing element C in the Nb-BCC matrix.
查看更多>>摘要：The growing need for stronger and more ductile structural materials has spurred an intense search for innovative,high-performance alloys.Traditionally,alloys face a pervasive trade-off:high strength often comes at the expense of ductility and vice versa.The advent of high-entropy alloys(HEAs)offering both high strength and ductility has transformed this landscape.In this work,we discuss the defor-mation mechanisms of HEAs,examine the foundations of the strength-ductility trade-off,and explore approaches for designing HEAs to surmount this limitation.Furthermore,we analyze the factors that govern HEA-deformation performance,which in turn influence the HEA design.We also propose a per-spective on future research directions concerning the mechanical behavior of HEAs,highlighting potential breakthroughs and novel strategies to advance the field.
查看更多>>摘要：Superhydrophobic surfaces with water-repelling ability have important applications,such as self-cleaning,antibacterial and corrosion protection.However,the using of harmful fluorinated materials and its poor mechanochemical stability limit its practical application.Herein,a fluorine-free,robust and self-healing superhydrophobic surface is prepared through a two-step method of laser processing and spraying coat-ing for anticorrosion and antibacterial applications.Laser processing is used to construct periodic micron-sized pillars for obtaining strong interface bonding between coating and substrate by mechanical inter-locking effect,and as an'armor',preventing the removal of the coating.The coating consists of epoxy resin(EP),hexadecyltrimethoxysilane(HDTMS)and γ-aminopropyltriethoxysilane treated Cu2O(KH550-Cu2O).The superhydrophobic surface can withstand various mechanical durability tests,such as multiple sandpaper abrasion and tape peeling cycles.It exhibits excellent corrosion inhibition efficiency(ηp＞99％)on Mg alloy,Tinplate and Al alloy,which results from superhydrophobicity and organic coating.The superhydrophobicity endows surface with excellent antibacterial adhesion performance in a static liquid environment.The bactericidal activity of KH550-Cu2O can effectively inactivate the bacteria in contact with the surface and the free bacteria,providing excellent antibacterial ability in a dynamic liquid envi-ronment.It still exhibits good anticorrosion and antibacterial abilities after multiple mechanical abrasion cycles due to the outstanding mechanical durability.Moreover,it exhibits outstanding self-healing ability to plasma etching and oil contamination,self-cleaning ability under air and oil conditions,and chemical stability against acids and alkalis solution.All the above excellent performances promote its application in a wider range of fields.
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