Influence of Shear Banding on the Formation of Brass-type Textures in Polycrystalline fcc Metals with Low Stacking Fault Energy

Texture evolution in nickel, copper and α-brass that are representative of face-centered-cubic （fcc） materials with different stacking fault energy （SFE） during cold rolling was systematically investigated. X-ray diffraction, scanning electron microscopy and electron backscatter diffraction techniques were employed to characterize microstructures and local orientation distributions of specimens at different thickness reductions. Besides, Taylor and Schmid factors of the {111} 〈110〉 slip systems and {111} 〈112〉 twin systems for some typical orientations were utilized to explore the relationship between texture evolution and deformation microstructures. It was found that in fcc metals with low SFE at large deformations, the copper-oriented grains rotated around the 〈110〉 crystallographic axis through the brass-R orientation to the Goss orientation, and finally toward the brass orientation. The initiation of shear banding was the dominant mechanism for the above-mentioned texture transition.

Oxidation behavior and microstructural evolution of FeCoNiTiCu five-element high-entropy alloy nanoparticles

High-entropy alloys(HEAs)have attracted extensive attention ascribed to their unique physical and chemical properties induced by the cocktail effect.However,their oxidation behaviors,in particular at nanoscale,are still lack because of multi-element complexity,which could also be completely differ-ent from the bulk counterparts.In this work,we synthesized FeCoNiTiCu five-element HEA nanopar-ticles(NPs)with uniform elemental distribution by arc-discharging approach,and further investigated their oxidation behaviors at 250 ℃,and 350 ℃.The morphology,structure and element distribution of NPs were analyzed by transmission electron microscopy(TEM),energy dispersive spectroscopy(EDS)and electron energy loss spectroscopy(EELS).The surface oxidation in FeCoNiTiCu NPs during the high-temperature process can induce nanoscale pores at core/shell interfaces by Kirkendall effect,and even the eventual coalescence into a single cavity.Additionally,the oxidation states of NPs with diameters(d)varying from 60 to 350 nm were analyzed in detail,revealing two typical configurations:hollow(d<150 nm)and yolk-shell structures(d>150 nm).The experimental results were complemented by first-principles calculations to investigate the diffusion behaviors of five elements,evidencing that the surface oxidation strongly alters the surface segregation preferences:(1)in the initial stage,Cu and Ni appear to prefer segregating on the surface,while Co,Ti and Fe tend to stay in the bulk;(2)in the oxidation process,Cu prefers to stay in the center,while Ti segregates to the surface ascribed to the reduced po-tential energies.The study gives new insights into oxidation of nanoscale HEA,and also provides a way for fabrication of high-entropy oxides with controllable architectures.

Effect of Al on Microstructure and Mechanical Properties of ATI 718Plus by Laser Additive Manufacturing

To clarify the mechanism of the role of Al element in the additive manufacturing of Ni-based superalloys,ATI 718Plus alloys with varying Al contents(1,3,and 5 wt%)were fabricated using the laser additive manufacturing and the effects of Al content on the microstructure and mechanical properties were systematically analyzed.The experimental and CALPHAD simulation results show that with the increase in Al addition,the freezing range of the alloys was lowered,but this has a paradoxical effect on the susceptibility of the alloy to hot-tearing and solid-state cracking.The addition of Al increased theγ′and Laves phase volume fractions and suppressed the precipitation of theηphase.Simultaneously improvingγ/γ′lattice misfits effectively promoted the transformation ofγ′phase from spherical to cubic.The precipitation of NiAl phase in the 5 wt%Al-added alloy was determined,the formation mechanism of NiAl phase was analyzed,and the solidification sequence of the precipitated phase in the alloy was summarized.In addition,with the increase in Al addition,the microhardness of the alloy increased gradually,the tensile strength increased at first and then decreased,but the plasticity deteriorated seriously.The insights gained from this study offer valuable theoretical guidance for the strategic compositional design of additively manufactured Ni-based superalloys destined for deployment under extreme conditions.

Oxygen addition for improving the strength and plasticity of TiZr-based amorphous alloy composites

The addition of a small amount of oxygen improves the mechanical properties,especially plasticity,of Ti_(45.7)Zr_(33)Ni_(3)Cu_(5.8)Be_(12.5) amorphous alloy composites(AACs)at room temperature(298 K).Compared to the plasticity of AACs without added O(5%),the plasticity of the composites with 0.73 at.%O(nominal composition)was much higher(11%).Even at O content higher than 0.73 at.%,the AACs exhibited good plasticity.The highest plasticity of∼12.3%was observed with 2.87 at.%O.Two distinct mechanisms are proposed to explain the enhanced plasticity of the AACs.At low O content,although deformation-induced phase transformation was suppressed,a substantial amount of α" martensite was formed.The microstructural features of α" martensite,such as thinner laths and homogeneous distribution,induced the formation of multiple shear bands in the amorphous matrix.At high O content,deformation-induced phase transformation was seriously suppressed.A dispersed nanoωphase was formed during rapid solidification in AACs with O content higher than 1.45 at.%.This resulted in a weakening in the anisotropy ofβdendrites and led to their homogenous deformation.Furthermore,multiple shear bands were formed in the amorphous matrix.Apart from plasticity,the strength of the AACs also increased with an increase in the O content.This phenomenon was explained in terms of three mechanisms,viz.the solid-solution-strengthening effect of O,fine-grain strengthening of β dendrites,and secondary phase strengthening by the nano ω phase.

Inter-granular exchange coupling and magnetic anisotropy of Ta/Ru/Co-23 at%Pt perpendicular thin films with different Ru underlayer thicknesses

In the present work, a series of Ta/Ru/Co- 23 at%Pt thin films with varied Ru underlayer thicknesses were fabricated by magnetron sputtering. All of the films show c-axis preferred orientation perpendicular to the film surface. The drop of c/a ratio and lattice expansion of Co- Pt layer with the increase in Ru underlayer thickness was revealed by X-ray diffraction （XRD）. The coercivity of the Ta/Ru/Co-Pt thin films increases drastically with Ru underlayer thickness increasing, due to the enhancement of effective magneto-crystalline anisotropy constant and exchange decoupling of magnetic nano-grains. The enhancement of effective magneto-crystalline anisotropy constant is ascribed to the lattice deformation of Co-Pt layer by mismatching the Ru layer and Co-Pt surface. Moreover, the exchange decoupling of magnetic nanograins is attributed to the further isolation of magnetic nano-grains.

Fe_(3)O_(4)@silica nanoparticles for reliable identification and magnetic separation of Listeria monocytogenes based on molecular-scale physiochemical interactions

Listeria monocytogenes(L.monocytogenes)is one of the top five dangerous foodborne pathogens which widely exists in most raw food and has approximately 30%mortality rate in high-risk groups.Food safety caused by foodborne pathogens is still a major problem faced by humans in all world.The conventional analytical methods currently used involve complex bacteriological tests and usually take several days for incubation and analysis.Thus,in order to prevent the spread of disease,the development of a detection method with high speed,high accuracy and sensitivity is urgent and necessary.Herein,we developed an approach for the identification and magnetic capture of L.monocytogenes by using core@shell Fe_(3)O_(4)@silica nanoparticles terminated with hydroxyl or amine groups.Our results show that both amine-and hydroxyl-terminated Fe_(3)O_(4)@silica core@shell nanoparticles functionalized with specific antibodies,present 95.2%±6.2%and 98.6%±0.3%capture efficacies,respectively.However,without conjugating the specific antibodies,the hydroxyl-terminated Fe_(3)O_(4)@silica nanoparticles exhibit 17.6%±1.6%efficacy,while the amine-terminated one remains 93.2%±9.2%capture efficiency ascribed to the high affinity.This study quantitatively uncovers the specific and non-specific recognitions relevant to the molecular-scale physiochemical interactions between the microorganisms and the functionalized particles,and the results from this work can be generalized and extended to other bacterial species by changing antibodies,also have important implications in developing advanced analytic methods.

Finite element analysis of effect of interfacial bubbles on performance of epoxy coatings under alternating hydrostatic pressure

The stresses around bubbles formed on a coating/substrate interface under hydrostatic pressure(HP)and alternating hydrostatic pressure(AHP)were calculated using the finite element method.The results reveal that HP promotes coating failure but does not mechanically destroy the interface,whereas AHP can provide tensile stress on bubbles formed at the interface and accelerate disbonding of the coating.Because of water resistance,a lag time exists for the coating that serves in an AHP environment.The coating can have a better protective performance if the lag time suits the AHP to minimize the impact of the AHP on the interface.

A nano-structured TiO_(2)/CuO/Cu_(2)O coating on Ti-Cu alloy with dual function of antibacterial ability and osteogenic activity

Bacteria-associated infection and poor osseointegration are two main reasons for orthopedic implant failure.Ti-Cu alloy exhibited excellent antibacterial property,but still presented unsatisfied osteogenic activities.Therefore,Ti-Cu alloy was surface modified by an alkali-heat treatment in this paper to improve the osteogenic ability without reduction in antibacterial ability.A TiO_(2)/CuO/Cu_(2)O composite coating with nanostructure was deposited on Ti-Cu alloy.The coating showed increased roughness and great hydrophilicity.Antibacterial tests indicated that the modified Ti-Cu alloy exhibited stronger antibacterial ability against Staphylococcus aureus(S.aureus)than Ti-Cu alloy.Meanwhile,cell experiments demonstrated that the composite coating promoted initial adhesion and spreading of MC3T3-E1 cells,enhanced alkaline phosphatase(ALP)activities as well as extracellular matrix(ECM)mineralization,and significantly upregulated osteogenesis-related gene expressions.It was suggested that the nano-structured TiO_(2)/CuO/Cu_(2)O coating on Ti-Cu alloy might provide a potential strategy for orthopedic implant failure.

Microstructure and nanoindentation hardness of shot-peened ultrafine-grained low-alloy steel

The effect of shot peening (SP) on microstructure and hardness of ultrafine-grained (UFG) low-alloy steel was investigated. With increasing shot-peening time from 0.5 to 1.5 h, grain size of UFG low-alloy steel decreases from 400 to 280 nm at surface whilst that of the layer with a depth of 160μm decreases from (230 ± 15) to (75 ± 5) nm. Interestingly, nanoindentation shows that hardness increases linearly with increasing the SP duration, reaching a value as high as (7.10 ± 0.1) GPa at the depth of 160 μm after the SP duration of 1.5 h. The thickness of the SP treated layer is measured as^300 μm. The Hall-Petch (H-P) relationship was established for the hardening layer. Correspondingly, abrasion resistance should be ~51% higher than that of as-prepared UFG low-alloy steel. As shown in SP processing, grain refinement is the key factor responsible for the strengthening of the studied steel.

Persistent excitation of spin waves for kπ-state skyrmions

In this study,we investigated the micromagnetic dynamics of kπ-state skyrmions in a magnetic nanodot under a circular spinpolarized current and found an excited spin wave that can propagate persistently along the direction of the radius toward the center.This dynamic process is associated with two energetically favorable states in an oscillating period of spin waves.In this case,the spin-polarized current plays a role similar to effective perpendicular magnetic anisotropy and decreases the minimum energy in the magnetic system.Our findings provide insight into understanding the dynamic behaviors of topological magnetic textures.

Constructing Ni_(4)W/WO_(3)/NF with strongly coupled interface for hydrogen evolution in alkaline media

The pursuit of storing renewable electricity in chemical bonds has encouraged the effort toward developing efficient electrocatalysts for alkaline hydrogen production.However,the additional step of water dissociation under alkaline conditions frequently limits the performance of electrocatalysts in alkaline media.Herein,we synthesize Ni_(4)W/WO_(3) with a strongly coupled interface on the Ni foam(NF)by phase transition of NiWO_(4),to enhance the activity for alkaline hydrogen production.It is discovered that the strong binding hydroxyl on WO_(3) sites facilitates the dissociation of water,which in turn promotes hydrogen evolution through the synergy effect of strong adsorption of H on Ni sites.The adsorption/desorption energy of Ni sites is further tuned by the formation of intermetallic Ni4W.Owing to the three-dimensional structure and tailored composition,the Ni_(4)W/WO_(3)/NF electrocatalyst exhibits a low overpotential of 31 mV at a current density of10 mA·cm^(-2),with a Tafel slope of 38 mV·dec^(-1).This work provides new opportunities to modulate the catalytic performance of Ni-based electrocatalysts by signifying the metal-oxide interface.

Microscopic insights into hydrophobicity of cerium oxide:Effects of crystal orientation and lattice constant

Cerium oxide possesses intrinsic hydrophobic properties ascribed to the unique electronic structure.However,the relationship between the crystal structure and hydrophobicity of cerium oxide has not been systematically studied.Herein,it is experimentally and theoretically demonstrated that the water contact angle(105.9°)of the(111)surface is higher than that(91.7°)of the(220)surface,associated with the lower surface free energy(28.44 mN/m)of(111)surface than that(38.48 mN/m)of(220)surface.Furthermore,cerium oxide films with(111)-terminated surface are annealed at 300℃ and 600℃ for1 h,respectively.The lattice constant increases(5.4594Å<5.4613Å<5.4670Å)with decreasing the annealing temperature(600℃>300℃>the as-deposited),leading to the increased water contact angle(96.7°<96.8°<99.0°).The First-principles calculation provides microscopic insights into the wetting mechanism,originating from the weakened adsorption capacity of the(111)surface for water molecules with the increasing lattice constant.

Mechanical Properties and Corrosion Behavior of Multi-Microalloying Mg Alloys Prepared by Adding AlCoCrFeNi Alloy

In this work,a series of multi-microalloying Mg alloys with a high degradation rate and high strength was prepared by adding AlCoCrFeNi HEA particles to the Mg melt followed by hot extrusion.The microstructure evolution and mechanical properties of the alloys were studied,meanwhile,the corrosion properties were evaluated by immersion weight loss and electrochemical tests.Results indicated that HEA particles in the Mg melt were decomposed and formed the Ni-rich phase,which was distributed uniformly in the Mg matrix.Compared with the pure Mg matrix,the Mg-3 HEA alloy exhibited excellent mechanical properties of the ultimate tensile strength~237 MPa and tensile yield strength~181 MPa,an increased rate of~49.1 and~96.7%,respectively,without sacrificing the elongation.And the ultimate compressive strength(UCS)and compressive yield strength increased by~31.5 and~43%to 392±3 and 103±2 MPa,respectively.Based on theoretical analysis,the high YS of the alloys was mainly attributed to fine-grain strengthening and second phase strengthening.Besides,based on the study of corrosion behavior,it was found that with the increase in HEA particle content,the degradation rate of the composites increased because of the promotion of micro-galvanic corrosion,and the Mg-3 HEA alloy showed a maximum degradation rate of~25.2 mg cmh.

Buildup of Sn@CNT nanorods by in-situ thermal plasma and the electronic transport behaviors

Monocrystal Sn nanorods encapsulated in the multi-walled carbon nanotubes(Sn@CNT NRs), were fabricated by a facile arc-discharge plasma process, using bulk Sn as the raw target and methane as the gaseous carbon source. The typical Sn@CNT NRs are 40–90 nm in diameter and400–500 nm in length. The CNTs protect the inner Sn nanorods from oxidation. Temperature dependent I–V curve and electronic resistance reveal that the dielectric behavior of Sn@CNT NRs is attributed to the multi-wall CNTs shell and follows Mott-David variable range hopping [ln R(T)∝T-1/4]model above the superconducting critical temperature of3.69 K, with semiconductor–superconductor transition(SST).Josephson junction of Sn/CNT/Sn layered structure is responsible for the superconducting behavior of Sn@CNT NRs.

Electrochemical corrosion behavior of 2A02 Al alloy under an accelerated simulation marine atmospheric environment

The corrosion behavior of 2 A02 Al alloy under simulated marine atmospheric environment has been studied using mass-gain, scanning electron microscope/energy dispersive spectroscopy(SEM/EDS), laser scanning confocal microscopy, X-ray diffraction spectroscopy and localized electrochemical methods. The results demonstrate that the relationship between the corrosion induced mass-gain and the corrosion time is in accordance with the power rule. The mass-gain increases gradually during the corrosion time,while the corrosion rate decreases. With ongoing of the corrosion, corrosion products film changed from a porous to a compact structure. The various spectroscopic data show that the corrosion products films composed mainly of Al(OH)_3, Al_2O_3 and AlCl_3. The electrochemical corrosion behavior of the 2 A02 Al alloy was studied by electrochemical impedance spectroscopy(EIS).

High strength-superplasticity combination of ultrafine-grained ferritic steel:The significant role of nanoscale carbides

There is currently a gap in our understanding of mechanisms that contribute to high strength and high plasticity in high strength UFG ferritic steel with nano-size Fe3 C carbides in situations that involve combination of various strain rates and high temperature.In this regard,we describe the mechanistic basis of obtaining high strength-high plasticity combination in an ultrafine-grained(UFG)(~500±30 nm)ferritic steel with nano-size carbides,which sustained large plastic deformation,exceeding 100%elongation at a temperature significantly below 0.5 of the absolute melting point(Tm).To address the missing gap in our knowledge,we conducted a series of experiments involving combination of strain rate and temperature effects in conjunction with electron microscopy and atom probe tomography(APT).Strain rate studies were carried out at strain rates in the range of 0.0017-0.17 s^(-1)and at different temperatures from 25℃to 600℃.Dynamic recrystallization occurred at 600℃,resulting in a significant decrease in yield and tensile strength.Nevertheless,the UFG ferritic steels had an advantage in tensile strength(UTS)and elongation-to-failure(εf)at 600℃,especially at strain rate of 0.0017 s^(-1),with high UTSof 510 MPa and excellent low temperature(<0.42 Tm)superplasticity(εf=110%).These mechanical properties are significantly superior compared to similar type of steels at identical temperature.A mechanistic understanding of mechanical behavior of UFG ferritic steels is presented by combining the effect of strain rate,temperature,and nano-size carbides.

Age hardening responses of as-extruded Mg-2.5Sn-1.5Ca alloys with a wide range of Al concentration

This article aims to explore the age hardening responses of both as-extruded and as-aged Mg-2.5 Sn-1.5 Ca-x Al alloys(x=2.0,4.0 and 9.0 wt%,termed TXA322,TXA324 and TXA329,respectively)through microstructural and mechanical characterization.Results indicate that grain size of as-extruded TXA322,TXA324 and TXA329 alloys were^16μm,~10μm and^12μm,respectively.A number of<a>and<c+a>dislocations were observed in all the as-extruded samples.Guinier–Preston(GP)zones were evidently identified in TXA322 alloy,while only a small number of Mg17 Al12 phases existed in both TXA324 and TXA329 alloys.An aging treatment facilitated the precipitation of a high number density of GP zones within the matrix of TXA322 alloy.In contrast,no obvious nano-precipitates were in as-aged TXA324 alloy.Numerous nano-Mg17 Al12 phases were formed through a following aging treatment in TXA329 alloy.In terms of mechanical properties,it is apparent that an increment in ultimate tensile strength of^46 MPa and^40 MPa was yielded in peak-aged TXA322 and TXA329 alloys,while no obvious variations in UTS were present in peak-aged TXA324 alloy,in comparison with the as-extruded counterparts.

Micromechanical behavior of a fine-grained China low activation martensitic(CLAM) steel

Micromechanical behavior of a fine-grained China Low Activation Martensitic (CLAM) steel under nanoindentation was studied in this work. The grain size of the as-prepared O.lTi-CLAM steel is ~5μm and the average diameter of the spherical precipitates is ~5 nm. Both elastic modulus and hardness decrease with increasing contact depth of the nanoindenter, following an exponential decreasing function. The abnormally large contact depths should be resulted from defect concentration under the indenter. The effect of nanosized precipitates on hardness is responsible for the pop-ins occurring in the load-depth curves, corresponding to the blockage of nanosized precipitates to the dislocation movement. Nanosized VC and M23C6precipitates with the volume fractions of 0.32% and 1.21% can be identified, respectively. Different strengthening mechanisms originated from the two types of nanosized precipitates. The blockage of dislocations by VC particles leads to an Orowan strengthening whilst dislocations could cut through theM23C6particles because of the large size of the particles. The strengthening effects originated from the VC and M23C6 precipitates lead to the strength increase of .448 MPa and .254 MPa, respectively.

Oxygen-sulfur Co-substitutional Fe@C nanocapsules for improving microwave absorption properties

Heteroatom substitution has been investigated to be a feasible way to optimize microwave absorption properties of core-shell structural nanocapsules at gigahertz.Although dielectric capacity has been increased at specific frequency with substituted absorbents,its broadband absorption performance is still relatively poor ascribed to the low dipole oscillation amplitude of single substituted heteroatom.In this study we demonstrate that sulfur and oxygen co-substituted heterostructure leads to high microwave absorption property of core-shell structural Fe@C nanocapsules at broadened frequency range,comparable to the single sulfur substitutional Fe@C nanocapsules.Experimental characterizations coupled with first-principles calculations reveal that the microwave absorption enhancement is triggered by the sulfur-oxygen co-substitution,which results in the serious symmetry breaking and thus leads to the charge separation at the co-substituted area.In particular,the nanocapsules exhibt the minimum reflection loss capcacity R(d B)of-52 d B at 6.8 GHz and the bandwith for R(d B)<-20 dB is in the frequency range of 3.1-12.7 GHz.The present study not only offers a deep insight into the relationship between heteroatom and microwave absorption property,but also puts forward a mentality for further designing microwave absorbents.

Enhancing the bake-hardening responses of a pre-aged Al-Mg-Si alloy by trace Sn additions

Effects of additions of trace Sn on the bake-hardening responses of a pre-aged Al-0.85 Mg-0.85 Si(in wt%)alloy were investigated through mechanical tests,differential scanning calorimetry,electrical resistivity and transmission electron microscopy.Results indicate that trace Sn additions reduced the number density of pre-aging clusters by inhibiting the formation of unstable counterpart during pre-aging treatment,leading to low strength and high supersaturation of solute atoms.In a subsequent paint-bake treatment,the presence of highly supersaturated solute atoms and high concentrated free vacancies moderated the activation energy barrier ofβ’’phase and thus kinetically accelerated the formation ofβ’’.Consequently,the trace Sn additions enhanced the bake-hardening responses of the pre-aged alloys significantly.The Sn-containing pre-aged Al-Mg-Si alloys with low strength and great bake-hardening responses hold promising potential for automotive body skin applications.