查看更多>>摘要：Effect of cooling rates,i.e.,air cooling and furnace cooling,after solution in α+β phase-field on variant selection,coarsening behavior of α phase and microstructure evolution were investigated in α+β TC21 alloy.The textures of primary α(αp)and lamellar α(αL)in β phase transformation microstructure(βt)were analysed separately,and the orientation relationship among αp,αL and the parent β phase were studied.In addition,the influence of the microstructure characteristics on the tensile properties was in-vestigated.The results showed that all parent β grains,despite their different orientations,produced 12 ideal αL variants with the same texture components and interweave to form a basketweave βt struc-ture under the air-cooling condition.The αp without Burgers orientation relationship(BOR)with β phase exhibited obviously texture component without overlapping the αL texture component.The volume frac-tion of αp in the furnace-cooled sample(about 50％)was higher than that of the air-cooled sample(about 12％),while the size of it slightly increased with decreasing the cooling rate.In each β grain,the thick αL in the same orientation formed an α colony.A typical 3 variant colonies which were related to each other were observed.Consequently,the αL spatial orientation distribution showed more heterogeneity.More-over,the BOR between αp and β and the same orientation of some αL and the surrounding αp grains resulting in the overlapping of αp texture component and αL texture component.At last,the relationship between microstructure and tensile properties was analysed.
查看更多>>摘要：Microalloying of Ti-6Al-4V alloy by Fe addition has attracted interest as a promising way to improve castability and comprehensive mechanical performance.The mission of this work is twofold by employ-ing the experimental examination and the phenomenological analysis,(1)to investigate the effect of Fe addition on the microstructure features and mechanical properties of the Fe-containing Ti-6Al-4V(TC4-xF)alloys subjected to casting and homogenization treatment,and(2)to unveil the critical microstruc-ture features in homogenization,hot-worked and aging treated alloys,respectively,that benefit the yield strength and the fracture toughness.Experimental observations evidence that the addition of 0.5 wt.％Fe is most effective in enhancing the tensile ductility and the mode Ⅰ fracture toughness.Further Fe addi-tion up to 0.7-0.9 wt.％results in plateau values of yield and ultimate strengths with some fluctuations.Phenomenological analyses screen out the microstructural strengthening and toughening determinants which exhibit distinct sensitivities on Fe content under different processing conditions.The solid solution strengthening is confirmed as the primary effect that governs the yield strength of the homogenization treated TC4-xF alloys,followed by the refined size of colony and α lamella,so does it for the hot-worked and the aging-treated alloys.The strengthening effect of Fe could be further promoted by hot-working but impaired by a prolonged annealing time or a lowered cooling rate.The type of crack propagation path and the α morphology are discerned to play their own leading roles in different cases to influence the performance of fracture toughness.A long crack propagation distance that traverses broad α/β lamellae embraces a high crack propagation resistance and gives rise to enhanced fracture toughness.The experi-mental results enrich the dataset of microstructure features and mechanical properties of Ti-6Al-4V rele-vant alloys.While upon the phenomenological analysis,the discovered microstructural strengthening and toughening factors provide deeper mechanism insights into the mechanical behaviors of Fe-modified Ti-6Al-4 V alloys and are of the technical importance to future machine-learning of microstructure-property relationship.
查看更多>>摘要：Laser solid forming(LSF)technology can be used to rapidly manufacture and repair high-strength steel parts with superior performance,but the value of the heat input during operation is difficult to quantify,which has a substantial impact on the microstructure and mechanical properties of the parts.A promis-ing method to improve the forming efficiency and quality of LSFed parts is to accurately control the heat input and explore its relationship with the microstructure and mechanical properties.To remove the interference of other variables from the experiment,the dimensionless heat input Q* was introduced.The Q* values were designed in advance to calculate the experimental parameters used to perform the LSF experiment.The microstructure was observed at different regions of the sample,and its mechanical properties were analyzed.From the results,the following conclusions were drawn.The Q* value was di-rectly related to the cooling rate and heat accumulation in the top structure,leading to the formation of different microstructures;it also modified the original structure at the bottom,affecting the subsequent thermal cycle and indirectly changing the tempered martensite morphology.The heat input also affected the mechanical properties of the sample.The hardness of the stable zone decreased with increasing Q*value,and the lowest value was 190 HV.Similarly,the tensile strength and yield strength of the LSFed samples decreased considerably with increasing Q* value,and the lowest values were 735 and 604 MPa,respectively.Only the elongation and reduction in the area increased after a slight decrease.The Q* value had a significant effect on heat treatment.When Q*=2.9,the increase in tensile strength and yield strength after heat treatment was the largest(29％and 44％,respectively).
查看更多>>摘要：We demonstrate the first successful attempt to partially substitute Cu into the Mn3AgN-antiperovskite system to form Mn3Ag(1-x)Cu(x)N thin films with an ultra-low temperature coefficient of resistance(TCR)for fabrication of ultra-precise passive components.Films were grown by reactive magnetron sputtering on alumina and glass substrates and were found to be amorphous in nature with highly negative TCR of-233 to-351 ppm/℃in their as-grown state.Increasing Cu alloying from x=0 to 1,resulted in increased sheet resistance,a negative shift of TCR and a change of grain morphology from spherical to elongated.Post-deposition heat treatment at 300-375℃,resulted in a positive shift of TCR and an ultra-low TCR of-4.66 ppm/℃for films with x=0.6.The heat treatment induces grain growth,surface roughness and the formation of a manganese oxide upper surface layer up until temperatures of 350℃,after which surface oxidation begins to dominate.The growth rate of the surface layer is controlled by the Cu concentration and heat treatment temperature,which both play a central role in the development of these novel ultra-low TCR Mn3Ag(1-x)Cu(x)N thin film structures.
查看更多>>摘要：We report nearly full densification of polycrystalline rhombohedral beta(β)-boron without the addition of sintering aids via spark plasma sintering(SPS).The analytical aberration corrected transmission elec-tron microscope observations have revealed in-situ growth of nanocrystalline boron-rich oxide precipi-tates that contain approximately 4 at.％of oxygen and beget the densification of β-boron.Further elec-tron energy loss spectroscopy and diffraction analysis confirmed that the newly formed boron-rich oxide(nominally B96O4)structure with B-O σ-bonding belongs to space group R3m.Depth sensitive nanoin-dentation showed boron-rich oxide phase has a hardness of about 41±2 GPa,which is 10％higher than that of β-boron matrix.The estimated hardness and fracture toughness of β-boron were approximately 31 GPa and 2.2 MPa m1/2,respectively,using Vickers microindentation,which falls in the range of those commercially used boron carbides.These results suggest that the enhanced densification and mechanical properties arise from the newly formed boron-rich oxide in β-boron during SPS experiments.
查看更多>>摘要：Combined theoretical and experimental efforts are put forward to study the critical factors influencing deformation mode transitions in face-centered cubic materials.We revisit the empirical relationship be-tween the stacking fault energy(SFE)and the prevalent deformation mechanism.With ab initio calcu-lated SFE,we establish the critical boundaries between various deformation modes in the model Cr-Co-Ni solid solution alloys.Satisfying agreement between theoretical predictions and experimental observa-tions are reached.Our findings shield light on applying quantum mechanical calculations in designing transformation-induced plasticity and twinning-induced plasticity mechanisms for achieving advanced mechanical properties.
查看更多>>摘要：Joining of ceramic and metal is a key component in microelectronic device manufacturing,in which the integrity of bonded interface is critical in the performance and stability of the devices.Current meth-ods with a problem of thick transition layer at the interface impeded heat flow,which degraded device service life seriously.Herein,we propose a laser-assisted bonding approach to join ceramic to metal di-rectly without any intermediate material.By focusing the laser on the surface of β-Si3N4 ceramic,the Si microcrystalline layer with stacked α-Si3N4 nanocrystals was prepared first.The face-centered cubic(fcc)Si and hexagonal close-packed(hcp)β-Si3N4 substrate take the coherent orientation relations of[001]fcc ‖[0001]hcp and(220)fcc‖(10(1)0)hcp.Then,the defect-free Si3N4/Cu bonded interface obtained by the reaction of the formed Si and Cu at elevated temperature in the 805-900℃range for 30 min demonstrated a strong and stable joining of ceramic to metal.The introduction of the laser provides a novel approach to join ceramics to metals,and the ceramic/metal component is expected to be a new configuration for package substrate in high-power device applications.
查看更多>>摘要：The amorphous/amorphous nanolaminates(A/ANLs)have aroused great attentions owing to their tunable structure and enhanced mechanical properties.However,the plastic deformation mechanism of A/ANLs have yet been clarified.Here,we systematically examined the mechanical properties and deformation behavior of series of NiNb/ZrCuNiAl A/ANLs via nanoindentaion test.It was found that both the amount and morphology of amorphous/amorphous interface(A/AIs)played crucial roles in the plastic deforma-tion of A/ANLs.Less and straighter A/AIs facilitated multiple shear banding deformation,of which the hardness increased with decreasing layer thickness,as the A/Als hindered the propagation of shear bands(SBs).Whilst,more and wavier A/AIs promoted homogeneous deformation,of which the hardness stayed at a much lower value and was relatively irrelevant with the layer thickness,for the promoted activa-tion of shear transformation zones by A/Als.Our results provide guidance for modifying the mechanical properties of amorphous alloys with interface engineering design.
查看更多>>摘要：Transition-metal phosphides(TMPs)-based hybrid structure have received considerable attention for effi-cient sodium storage owing to their high capacity and decent reversibility.However,the volume expan-sion&the poor electronic conductivity of TMPs,the poor-rate capability,and fast capacity decay greatly hinder its practical application.To address these issues,a low-cost and facile strategy for the synthesis of Ni,N-codoped graphitized carbon(C)and cobalt phosphide(CoP)embedded in carbon fiber(Ni-CoP@C-NcCF)as self-supporting anode material is demonstrated for the first time.The graphitized carbon and carbon fiber improve the electrical conductivity and inhibit the volume expansion issues.In addition to that,the microporous structure,and ultrasmall sized Ni-CoP offer a high surface area for electrolyte wettability,short Na-ion diffusion path and fast charge transport kinetics.As a result,outstanding elec-trochemical performance with an average capacity decay of 0.04％cycle-1 at 2000 mA g-1,an excellent rate capability of 270 mAh g-1@2000 mA g-1 and a high energy density of～231.1 Wh kg-1 is achieved with binder-free self-supporting anode material.This work shows a potential for designing binder-free and high energy density sodium-ion batteries.
查看更多>>摘要：As the lightest structural metallic materials,Mg-Li alloys have a bright development prospect in the fields of aerospace,weapon equipment,electronic technology and transportation.In this paper,the research progress of deformation processing and heat treatment of Mg-Li alloys is reviewed,with particular em-phasis on the factors affecting the plastic deformation,the effects of plastic deformation on microstruc-tural evolution and mechanical properties,and the heat treatment behavior of Mg-Li alloys.The problems existing in the scale application of Mg-Li alloys are pointed out,and the research focus of Mg-Li alloys in the future are also prospected.
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