Phase thermal stability and mechanical properties analyses of(Cr,Fe,V)–(Ta,W)multiple-based elemental system using a compositional gradient film

High-entropy alloys(HEAs)generally possess complex component combinations and abnormal properties.The traditional methods of investigating these alloys are becoming increasingly inefficient because of the unpredictable phase transformation and the combination of many constituents.The development of compositionally complex materials such as HEAs requires high-throughput experimental methods,which involves preparing many samples in a short time.Here we apply the high-throughput method to investigate the phase evolution and mechanical properties of novel HEA film with the compositional gradient of(Cr,Fe,V)-(Ta,W).First,we deposited the compositional gradient film by co-sputtering.Second,the mechanical properties and thermal stability of the(Cr0.33Fe0.33V0.33)x(Ta0.5W0.5)100−x(x=13-82)multiplebased-elemental(MBE)alloys were investigated.After the deposited wafer was annealed at 600℃for 0.5 h,the initial amorphous phase was transformed into a body-centered cubic(bcc)structure phase when x=33.Oxides were observed on the film surface when x was 72 and 82.Finally,the highest hardness of as-deposited films was found when x=18,and the maximum hardness of annealed films was found when x=33.

具有规则微结构表面聚丙烯塑件的超声模压粉末成型

利用自制的组合式模具,通过超声模压粉末成型工艺,制得形状尺寸可控的聚丙烯微塑件,成功复制了模芯表面的微沟槽阵列结构。设计单因素实验,研究了超声能量、焊接压力、保压时间对聚丙烯微结构塑件成型的影响。结果表明,适当增加超声能量与焊接压力,可有效提高熔体的填充能力。当超声能量为1000 J、焊接压力为115 kPa、保压时间为8 s时,所制得的微结构塑件具有较好的表面形貌复制率。差示扫描量热和X射线衍射分析表明,超声能量的增加不会改变聚丙烯的晶体结构;随着超声能量的增加,微结构塑件的结晶度降低、晶粒细化。

Machine learning accelerated DFT research on platinum-modified amorphous alloy surface catalysts

Pt-modified amorphous alloy(Pt@PdNiCuP)catalyst exhibits excellent electro-catalytic activity and high experimental durability for hydrogen evolution reaction(HER).However,the physical origin of the catalytically active remains unclear.In this paper,we constructed a distance contribution descriptor(DCD)for the feature engineering of machine learning(ML)potential,and calculated the Gibbs free energies(ΔGH)of 46,000*H binding sites on the Pt@Pd Ni Cu P surface by ML-accelerated density functional theory(DFT).The relationship betweenΔGHand DCD revealed that in the H-Pt distance region of 2.0-2.5 A where the parabolic tail and disordered scatters coexist,the H-metal bonding configuration is mainly the bridge-or hollow-bonding type.The contribution analysis of DCD indicates that the joint effect of Pt,Pd and Ni atoms determines the catalytical behavior of amorphous alloy,which agrees well with experimental results.By counting atomic percentages in different energy intervals,we obtained the atomic ratio for the best catalytic performance(Pt:Pd:Ni:Cu:P=0.33:0.17:0.155:0.16:0.185).Projected density of states(PDOS)show that H 1s orbital,Pt 5d orbital,and Pd 4d orbital form a bonding state at-2 e V.These results provide new ideas for designing more active amorphous alloy catalysts.

Effect of Room Temperature Ultrasonic Vibration Compression on the Microstructure Evolution and Mechanical Properties of AZ91 Alloy

To investigate the potential of direct ultrasonic vibration on improving the performance of magnesium alloys,this study first employed the ultrasonic vibration compression(UVC)on the solid solution treated AZ91 alloy,and explored its microstructure evolution and mechanical properties under UVC.Within only two seconds,the UVC alloys showed large deformation strains of 34.8–54.4%,and sudden increase of sample temperature to 243℃.Microstructure characterizations proved that UVC promoted the formation of abundant shear bands,fine grains,and the bimodal distribution of Mg17Al12 precipitates consisting of submicron particles located within the shear bands and nano-sized ones within the matrix.Owing to the unique microstructure,the micro-hardness(and nano-hardness)value of UVC alloy was increased by 37.7%(35%)when compared with the solution-treated alloy.Moreover,the nano-modulus of the developed AZ91 alloy was also significantly increased to 62 GPa by statistical nanoindentation tests,which could be ascribed to increased Mg_(17)Al_(12) precipitates and decreased c/a value to some extent.In general,this work provides a new insight into the design and preparation of high-performance magnesium alloys by UVC at room temperature.

Ultrasonic vibration enabled under-liquid forming of metallic glasses

Advancements in forming technology offer significant advantages for the manufacturing industry,including enhanced efficiency,energy conservation,and improved material utilization[1].However,traditional additive manufacturing[2],thermoplastic forming[3],and laser cutting[4]encounter challenges when applied in under-liquid environments,mainly due to difficulties in temperature control and heat source provision.

Absence of ultrasonic-vibration-induced plasticity in metallic glacial glasses

Metallic glasses (MGs) have been found to exhibit unexpected ultrasonic-vibration-induced plasticity (UVIP),which provides a promising way to realize room temperature processing and molding of MGs.However,whether all MGs possessing UVIP remains a mystery.

High-throughput screening for biomedical applications in a Ti-Zr-Nb alloy system through masking co-sputtering

A method of co-sputtering deposition combined with physical masking was applied to the parallel preparation of a ternary Ti-NbZr system alloy. Sixteen independent specimens with varying compositions were obtained. Their microstructure, phase structure,Young’s modulus, nanoindentation hardness, and electrochemical behavior in a phosphate buffer solution(PBS) were studied in detail. It was revealed that the Ti-Zr-Nb alloys possess a single BCC structure. As confirmed via nanoindentation tests, the Young’s modulus of the specimens ranged from 80.3 to 94.8 GPa and the nanoindentation hardness ranged from 3.6 to 5.0 GPa.By optimizing the composition of the specimens, the Ti34Zr52Nb14 alloy was made to possess the lowest modulus in this work(76.5 GPa). Moreover, the Ti34Zr52Nb14 alloy showed excellent corrosion resistance in PBS without any tendency for pitting at anodic potentials up to 1 Vsce. These preliminary advantages offer the opportunity to explore new orthopedic implant alloys based on Ti-Zr-Nb alloys. Moreover, this work provides an effective method for the parallel preparation of biomedical alloys.

Interface design enabled manufacture of giant metallic glasses

Developing materials with excellent properties has been the untiring pursuit of mankind.Metallic glasses(MGs)would be the ideal metallic materials if their size could be scaled up to be comparable to traditional metals.To address this challenge,a variety of approaches have been attempted over the past decades,including thermodynamicsbased alloy,3D printing and the recent artificial intelligenceguided optimal alloy.In this study,a facile and flexible route was demonstrated to manufacture giant MGs(GMGs)with diameters more than 100 mm through the thermo-joining process.The jointed GMG samples feature almost the same performance as the as-cast ones.The ability of manufacturing complex 3D components such as the Chinese Zodiacs was also demonstrated.Our approach might overcome the longstanding problem of glass forming ability(GFA)limitations in alloy systems and pave new concept and route to fabricate size unlimited MGs.

Machine learning atomic dynamics to unfold the origin of plasticity in metallic glasses:From thermo-to acousto-plastic flow

Metallic glasses(MGs)have an amorphous atomic arrangement,but their structure and dynamics in the nanoscale are not homogeneous.Numerous studies have confirmed that the static and dynamic heterogeneities of MGs are vital for their deformation mechanism.The“defects”in MGs are envisaged to be structurally loosely packed and dynamically active to external stimuli.To date,no definite structure-property relationship has been established to identify liquid-like“defects”in MGs.In this paper,we proposed a machine-learned“defects”from atomic trajectories rather than static structural signatures.We analyzed the atomic motion behavior at different temperatures via a k-nearest neighbors machine learning model,and quantified the dynamics of individual atoms as the machine-learned temperature.Applying this new temperature-like parameter to MGs under stress-induced flow,we can recognize which atoms respond like“liquids”to the applied loads.The evolution of liquid-like regions reveals the dynamic origin of plasticity(thermo-and acousto-plasticity)of MGs and the correlation between stress-induced heterogeneity and local environment around atoms,providing new insights into thermo-and acousto-plastic forming.

Cutting force and specific energy for rotary ultrasonic drilling based on kinematics analysis of vibration effectiveness

Rotary ultrasonic drilling(RUD)has become an effective approach for machining advanced composites which are widely using in the field of aeronautics.The cutting kinematics and the corresponding material removal mechanisms are distinct in different drilling areas during RUD.However,these fundamentals have not been fully considered in the existing studies.In this research,two distinct forms of interaction induced by ultrasonic vibration were considered as impact-separation and vibratory lapping between the abrasives and workpiece.And the conditions to guarantee the effectiveness of these interactions were obtained to eliminate diminishing effects of ultrasonic vibration.Based on indentation fracture theory,the penetration depth of abrasives and the axial drilling force model was derived for RUD.The verification tests of C/SiC composites resulted in a prediction error within 15%.Due to the minimal volume of material removed during each vibration cycle,the drilling force was more stable in vibration assisted mode.The specific drilling energy of RUD was firstly calculated based on the measured drilling load.It was found the drilling parameters should be matched with vibration frequency and amplitude to make better usage of the advantages of ultrasonic vibration,which is critical in the vibration assisted processing of advanced materials.

Manufacture of porous metallic glass using dissolvable templates

A facile,precise,and controllable manufacturing technology is desired for hierarchical functional surfaces.In this work,we successfully manufactured porous metallic glass using a water-dissolution material as template and the excellent thermoplastic property of metallic glass.The prepared micro/nanostructures have excellent tunability,and the proposed approach can be used to prepare large-area disordered porous structures and ordered regular arrays with nanoscale replication accuracy.In particular,the disordered porous structure prepared by the dissolvable template strategy exhibits a water contact angle of~140°and an oil contact angle of~0°,making it suitable for oil/water separation.It also shows stable wettability after being soaked in strong acid or alkali environments and maintains a~130°water contact angle and a~4°oil contact angle even after severe wear.The proposed strategy also possesses excellent recycling properties.We reconstructed porous structures on the same surface three times and found no significant change in wettability for each reconstructed porous structure.Our research provides a facile and controllable approach for the preparation of hierarchical porous structures and paves the way for the design of other functional surfaces.

Coexistence of superconductivity and antiferromagentic order in Er_(2)O_(2)Bi with anti-ThCr_(2)Si_(2) structure

We investigated the coexistence of superconductivity and antiferromagnetic order in the compound Er_(2)O_(2)Bi with anti-ThCr_(2)Si_(2)-type structure through resistivity,magnetization,specific heat measurements and first-principle calculations.The superconducting transition temperature Tc of 1.23 K and antiferromagnetic transition temperature TN of 3 K are observed in the sample with the best nominal composition.The superconducting upper critical field H_(c2)(0)and electron-phonon coupling constantλe−ph in Er_(2)O_(2)Bi are similar to those in the previously reported non-magnetic superconductor Y_(2)O_(2)Bi with the same structure,indicating that the superconductivity in Er_(2)O_(2)Bi may have the same origin as in Y_(2)O_(2)Bi.The first-principle calculations of Er_(2)O_(2)Bi show that the Fermi surface is mainly composed of the Bi 6p orbitals both in the paramagnetic and antiferromagnetic state,implying minor effect of the 4f electrons on the Fermi surface.Besides,upon increasing the oxygen incorporation in Er_(2)O_(x)Bi,Tc increases from 1 to 1.23 K and TN decreases slightly from 3 K to 2.96 K,revealing that superconductivity and antiferromagnetic order may compete with each other.The Hall effect measurements indicate that hole-type carrier density indeed increases with increasing oxygen content,which may account for the variations of Tc and TN with different oxygen content.

Ultra-fast amorphization of crystalline alloys by ultrasonic vibrations

The amorphization of alloys is of both broad scientific interests and engineering significance.Despite considered as an efficient strategy to regulate and even achieve record-breaking properties of metallic materials,a facile and rapid method to trigger solid-state amorphization is still being pursued.Here we report such a method to utilize ultrasonic vibration to trigger amorphization of intermetallic compound.The ultrasonic vibrations can cause tunable amorphization at room temperature and low stress(2 MPa)conveniently.Remarkably,the ultrasonic-induced amorphization could be achieved in 60 s,which is 360 times faster than the ball milling(2.16×10^(4) s)with the similar proportion of amorphization.The elements redistribute uniformly and rapidly via the activated short-circuit diffusion.Both experimental evidences and simulations show that the amorphous phase initiates and expands at nanograin boundaries,owing to the induction of lattice instability.This work provides a groundbreaking strategy for developing novel materials with tunable structures and properties.

Ultrasonic vibration-assisted multi-scale plastic forming of high-entropy alloys in milliseconds

Due to their excellent properties of specific strength,fracture resistance,corrosion and oxidation resistance,the high-entropy alloys have attracted widespread attention as engineering materials.For the sake of industrial applications,one of the essential stages would be the forming of them,especially the construction of multi-sc ale structures from macroscale to nanoscale.

Superior high-temperature wear resistance of an Ir-Ta-Ni-Nb bulk metallic glass

Wear resistance is a critical consideration in engineering applications.In this study,we demonstrated an Ir-Ta-Ni-Nb bulk metallic glass(BMG)with outstanding high-temperature wear resistance and revealed its promising applications in extreme environments.The wear behavior and mechanism were systemati-cally investigated from room temperature(RT)to 750℃.The results show that the wear rate increases from∼2.65×10^(-6)mm^(3)N^(-1)m^(-1)to∼10.56×10^(-6)mm^(3)N^(-1)m^(-1)in the temperature span RT to 400℃,following abrasive wear and flash temperature-induced oxidative wear during the friction.However,at the higher temperature of 600℃,further heating due to frictional heat leads to a softening of the wear surface,resulting in a maximum wear rate of∼20.99×10^(-6)mm^(3)N^(-1)m^(-1)under softness-driven abrasive wear as well as oxidative wear.Interestingly,the wear resistance at an even higher temperature of 750℃shows a paradoxical improvement of∼7.08×10^(-6)mm^(3)N^(-1)m^(-1),which is attributed to the formation of an oxide layer with a thickness of several microns,avoiding violent wear of BMG.The re-sults demonstrate the unreported outstanding high-temperature wear resistance of the Ir-Ta-Ni-Nb BMG,especially its excellent capability to resist wear at 750℃,leading to the promising applications of BMG in the fields of aerospace,metallurgy,and nuclear industries.

Disparities in employment outcomes among critical care graduates with different training backgrounds

Background:We sought to characterize the impact of critical care training pathways on subsequent employment opportunities.Methods:A survey assessing the postfellowship work environment and barriers to employment in a preferred setting was electronically distributed on September 16,2019,to program directors and coordinators at all US adult critical care fellowships with instructions to for-ward it to the prior year’s graduates.Results:Data collection was interrupted by the coronavirus disease 2019 pandemic.Fifty-nine participants were included,reflecting a low rate of return.Most worked in urban areas(76.6%)at academic hospitals(81.7%).Graduates of internal medicine critical care(IMCC)were more likely than pulmonary critical care(PCC)to report their fellowship as a barrier to employment(50%vs 0%;P<0.05).Emergency medicine graduates were more likely than internal medicine to report their residency as a barrier to employment(83.3%vs 4.6%;P<0.05).Inability to find a desired position at an academic center(50%vs 5.9%;P<0.05)and in the preferred metropolitan setting(37.5%vs 0%;P<0.05)were more common among IMCC than PCC.Conclusion:In this survey of critical care graduates,residency in emergency medicine and fellowship in IMCC were associated with in-creased barriers to finding desired employment.

High-entropy alloy and amorphous alloy composites fabricated by ultrasonic vibrations

We successfully fabricate high-entropy alloys and amorphous alloy composites by adopting the proposed ultrasonic vibration method.The low-stress,low-temperature method enables us to create composites that combine both amorphous and crystalline properties.Microscopic observations and computed tomography measurements indicate good bonding quality without pores or cracks in the composites.Due to the unique structure which mixes soft and rigid phases,the composite exhibits improved mechanical performance compared to that obtained from a pure single phase.Our results are promising for the manual design and fabrication of smart materials containing multiple phases and compositions.

Polyoxypregnanes as safe, potent, and specific ABCB1-inhibitory pro-drugs to overcome multidrug resistance in cancer chemotherapy in vitro and in vivo

Multidrug resistance(MDR)mediated by ATP binding cassette subfamily B member 1(ABCB1)is significantly hindering effective cancer chemotherapy.However,currently,no ABCB1-inhibitory drugs have been approved to treat MDR cancer clinically,mainly due to the inhibitor specificity,toxicity,and drug interactions.Here,we reported that three polyoxypregnanes(POPs)as the most abundant constituents of Marsdenia tenacissima(M.tenacissima)were novel ABCB1-modulatory pro-drugs,which underwent intestinal microbiota-mediated biotransformation in vivo to generate active metabolites.The metabolites at non-toxic concentrations restored chemosensitivity in ABCB1-overexpressing cancer cells via inhibiting ABCB1 efflux activity without changing ABCB1 protein expression,which were further identified as specific non-competitive inhibitors of ABCB1 showing multiple binding sites within ABCB1 drug cavity.These POPs did not exhibit ABCB1/drug metabolizing enzymes interplay,and their repeated administration generated predictable pharmacokinetic interaction with paclitaxel without obvious toxicity in vivo.We further showed that these POPs enhanced the accumulation of paclitaxel in tumors and overcame ABCB1-mediated chemoresistance.The results suggested that these POPs had the potential to be developed as safe,potent,and specific pro-drugs to reverse ABCB1-mediated MDR.Our work also provided scientific evidence for the use of M.tenacissima in combinational chemotherapy.

Ultrasonic-assisted plastic flow in a Zr-based metallic glass

Ultrasonic vibration can be used for the micro-molding of metallic glasses(MGs)due to stress-softening and fast surface-diffusion effects.However,the structural rearrangement under ultrasonic vibration and its impact on the mechanical response of metallic glasses remain a puzzle.In this work,the plastic flow of the Zr35Ti30Cu8.25Be26.75 metallic glass with the applied ultrasonic-vibration energy of 140 J was investigated by nanoindentation.Both Kelvin and Maxwell-Voigt models have been adopted to analyze the structural evolution during the creep deformation.The increase of the characteristic relaxation time and the peak intensity of relaxation spectra can be found in the sample after ultrasonic vibration.It effectively improves the activation energy of atomic diffusion during the glass transition(Eg)and the growth of the crystal nucleus(Ep).A more homogenous plastic deformation with a weak loading-rate sensitivity of stress exponent is observed in the ultrasonic-vibrated sample,which coincides with the low pile-up and penetration depth as shown in the cross profile of indents.The structural rearrangement under resonance actuation demonstrated in this work might help us better understand the defect-activation mechanism for the plastic flow of amorphous systems.

Ultrasonic-assisted rapid cold welding of bulk metallic glasses

Glass-forming ability is a long-standing concern in the field of metallic glasses(MGs),which greatly limits their maximum casting size and extensive applications.In this work,we report an ultrasonic-assisted rapid cold welding of bulk MGs without using any additives.MGs with various compositions are welded together under a 20,000-Hz highfrequency ultrasonic vibration without losing their amorphous nature.The ultrasonic technology offers the advantages of rapid bonding(<1 s)at low temperature(near room temperature)and low stress(<1 MPa).According to the phenomenon observed in the experiment,the activated fresh atoms diffuse through the broken channel port under continuous rupture of the oxide layer,and the ultrasonic vibration accelerates the atomic-diffusion process.Finally,stable bonding of the MG interface is realized.This universal ultrasonic-assisted welding process can realize the composition design of dissimilar MGs as well as tuning of new materials with new performance.