Eutectic high entropy alloys are noted for their excellent castability and comprehensive mechanical properties.The excellent mechanical properties are closely related to the activation and evolution of deformation mec...Eutectic high entropy alloys are noted for their excellent castability and comprehensive mechanical properties.The excellent mechanical properties are closely related to the activation and evolution of deformation mechanisms at the atomic scale.In this work,AlCoCrFeNi2.1 alloy is taken as the research object.The mechanical behaviors and deformation mechanisms of the FCC and B2 single crystals with different orientations and the FCC/B2 composites with K-S orientation relationship during nanoindentation processes are systematically studied by molecular dynamics simulations.The results show that the mechanical behaviors of FCC single crystals are significantly orientation-dependent,meanwhile,the indentation force of[110]single crystal is the lowest at the elastic-plastic transition point,and that for[100]single crystal is the lowest in plastic deformation stage.Compared with FCC,the stress for B2 single crystals at the elastic-plastic transition point is higher.However,more deformation systems such as stacking faults,twins and dislocation loops are activated in FCC single crystal during the plastic deformation process,resulting in higher indentation force.For composites,the flow stress increases with the increase of B2 phase thickness during the initial stage of deformation.When indenter penetrates heterogeneous interface,the significantly increased deformation system in FCC phase leads to a significant increase in indentation force.The mechanical behaviors and deformation mechanisms depend on the component single crystal.When the thickness of the component layer is less than 15 nm,the heterogeneous interfaces fail to prevent the dislocation slip and improve the indentation force.The results will enrich the plastic deformation mechanisms of multi-principal eutectic alloys and provide guidance for the design of nanocrystalline metallic materials.展开更多
Recently, the surface chemical functionalization and morphology control of precious metal nanostructures have been recognized as two efficient strategies for improving their electroactivity and/or selectivity. In this...Recently, the surface chemical functionalization and morphology control of precious metal nanostructures have been recognized as two efficient strategies for improving their electroactivity and/or selectivity. In this work, 1, 10-phenanthroline monohydrate(PM) functionalized Pt nanodendrites(Pt-NDs) on carbon cloth(CC)(denoted as PM@Pt-NDs/CC) and polyethylenimine(PEI) functionalized Pt-NDs on CC(denoted as PEI@Pt-NDs/CC) are successfully achieved by immersing Pt-NDs/CC into PM and PEI aqueous solutions, respectively. PEI functionalization of Pt-NDs/CC improves its electroactivity for hydrogen evolution reaction(HER) due to local proton enrichment whereas PM functionalization of Pt-NDs/CC improves its electroactivity for formic acid oxidation reaction(FAOR) by facilitating dehydrogenation pathway. With such high activity, a two-electrode electrolyzer is assembled using PM@Pt-NDs/CC as the anodic electrocatalyst and PEI@Pt-NDs/CC as the cathodic electrocatalyst for electrochemical reforming of formic acid, which only requires 0.45 V voltage to achieve the current density of 10 mA cm^(-1) for highpurity hydrogen production, much lower than conventional water electrolysis(1.59 V). The work presents an example of interfacial engineering enhancing electrocatalytic activity and indicates that electrochemical reforming of formic acid is an energy-saving electrochemical method for high-purity hydrogen production.展开更多
The wave-absorbing materials are kinds of special electromagnetic functional materials and have been widely used in electromagnetic pollution control and military fields.In-situ integrated hierarchical structure const...The wave-absorbing materials are kinds of special electromagnetic functional materials and have been widely used in electromagnetic pollution control and military fields.In-situ integrated hierarchical structure construction is thought as a promising route to improve the microwave absorption performance of the materials.In the present work,layer-structured Co-metal-organic frameworks(Co-MOFs)precursors were grown in-situ on the surface of carbon fibers with the hydrothermal method.After annealed at 500℃ under Ar atmosphere,a novel multiscale hierarchical composite(Co@C/CF)was obtained with the support of carbon fibers,keeping the flower-like structure.Scanning electron microscope,transmission electron microscope,X-ray diffraction,Raman,and X-ray photoelectron spectroscopy were performed to analyze the microstructure and composition of the hierarchical structure,and the microwave absorption performance of the Co@C/CF composites were investigated.The results showed that the growth of the flower-like structure on the surface of carbon fiber was closely related to the metal-to-ligand ratio.The optimized Co@C/CF flower-like composites achieved the best reflection loss of−55.7 dB in the low frequency band of 6–8 GHz at the thickness of 2.8 mm,with the corresponding effective absorption bandwidth(EAB)of 2.1 GHz.The EAB of 3.24 GHz was achieved in the high frequency range of 12–16 GHz when the thickness was 1.5 mm.The excellent microwave absorption performance was ascribed to the introduction of magnetic components and the construction of the unique structure.The flower-like structure not only balanced the impedance of the fibers themselves,but also extended the propagation path of the microwave and then increased the multiple reflection losses.This work provides a convenient method for the design and development of wave-absorbing composites with in-situ integrated structure.展开更多
Compositionally-complex alloys(CCAs)with the face-centered cubic(fcc)structure exhibit excellent frac-ture toughness and stable mechanical property across a broad temperature range from cryogenic to room temperatures....Compositionally-complex alloys(CCAs)with the face-centered cubic(fcc)structure exhibit excellent frac-ture toughness and stable mechanical property across a broad temperature range from cryogenic to room temperatures.However,yield strength of those alloys is usually low,making them difficult to meet the demands of practical engineering application.In a prototype CCA with the nominal chemical composition of Co10Cr10Fe49Mn30N1(atom percent),a multi-scaled heterostructure from sample to atomic scales was obtained by performing triaxial cyclic compression and short-term annealing on the blocky alloy.The ma-terial exhibits a heterogeneous distribution of strain at the sample scale.At the grain scale,dense twins and twin-twin network,laths featured with local chemical order as well as dislocation cells jointly hinder plastic deformation.At the nanoscale,the chemical order within grains also impedes dislocation motion.During plastic deformation,different sample positions within the heterogeneous material and various regions at each position undergo coordinated deformation,resulting in significant hetero-deformation in-duced strengthening.Simultaneously,the continuously activated dislocations,stacking faults and nano-twins lead to a high yield strength of 1020 MPa in the material while maintaining a fracture elongation of 30%.This study provides new insights for the design and development of high-performance metallic materials.展开更多
Ti/Cu multilayered composites were fabricated via accumulative roll bonding(ARB). During codeformation of the constituent metals, the hard Ti layers necked preferentially and then fragmented with the development of sh...Ti/Cu multilayered composites were fabricated via accumulative roll bonding(ARB). During codeformation of the constituent metals, the hard Ti layers necked preferentially and then fragmented with the development of shear bands. Transmission electron microscopy showed that with increasing ARB cycles, grains in Ti were significantly refined even though dynamic recrystallization has occurred. For Cu the significant grain refinement was only found within the shear banded region when the composite was processed after five ARB cycles. Due to the diffusion of Cu atoms into Ti at the heterophase interfaces, amorphization with a width less than 10 nm was identified even in the composite processed by one cycle. At higher ARB cycles, the width of amorphous region increased and intermetallic compounds CuTi appeared from the region. The lattice defects introduced at the heterophase interfaces under roll bonding was responsible for the formation of the nano-scaled compounds. X-ray diffraction showed that an abnormal {1120} fiber texture was developed in Ti layers, while significant brass-type textures were developed in Cu layers. Some orientations along the {1120} fiber favored the prismatic < a> slip for Ti.Tensile tests revealed the elevated strength without a substantial sacrifice of ductility in the composites during ARB. The unique mechanical properties were attributed to the significantly refined grains in individual metals, the good bonding between the constituent metals, as well as the development of an abnormal {1120} fiber texture in Ti layers.展开更多
High-entropy alloys(HEAs)have attracted great research interest owing to their good combination of high strength and ductility at both room and cryogenic temperatures.However,expensive raw materials are always added t...High-entropy alloys(HEAs)have attracted great research interest owing to their good combination of high strength and ductility at both room and cryogenic temperatures.However,expensive raw materials are always added to overcome the strength-ductility trade-off at low temperatures,leading to an increased production cost for the cryogenically used alloys.In this work,a series of nitrogen-doped Fe Mn Co Cr HEAs have been processed by homogenization annealing,cold rolling and recrystallization annealing followed by water quenching.The microstructural evolution and mechanical properties of the alloys are studied systematically.The Fe_(49)Mn_(30)Co_(10)Cr_(10)N1alloy shows excellent mechanical properties at both 293 K and 77 K.Particularly,the yield and ultimate tensile strength of 1078 and 1630 MPa are achieved at the cryogenic temperature,respectively,while a satisfactory uniform elongation of 33.5%is maintained.The ultrahigh yield strength results from the microstructure refinement caused by the activation of athermal martensitic transformation and mechanical twinning that occur in the elastic regime together with the increased lattice friction due to the cryogenic environment.In the plastic regime,the dynamic Hall-Petch effect caused by twinning,martensitic transformation,and reverse transformation together with the high barrier to dislocation motion jointly contribute to the ultrahigh tensile strength.Simultaneously,the transformation induced plasticity(TRIP)and the twinning induced plasticity(TWIP)effects jointly contribute to the ductility.The design strategy for attaining superior mechanical properties at low temperatures,i.e.by adjusting stacking fault energy in the interstitial metastable HEAs,guides the development of high-performance and low-cost alloys for cryogenic applications.展开更多
Face-centered cubic (f.c.c.) high entropy alloys (HEAs) are attracting more and more attention owing to their excellent strength and ductility synergy, irradiation resistance, etc. However, the yield strength of f.c.c...Face-centered cubic (f.c.c.) high entropy alloys (HEAs) are attracting more and more attention owing to their excellent strength and ductility synergy, irradiation resistance, etc. However, the yield strength of f.c.c. HEAs is generally low, significantly limiting their practical applications. Recently, the alloying of W has been evidenced to be able to remarkably improve the mechanical properties of f.c.c. HEAs and is becoming a hot topic in the community of HEAs. To date, when W is introduced, multiple strengthening mechanisms, including solid-solution strengthening, precipitation strengthening (μphase,σphase, and b.c.c. phase), and grain-refinement strengthening, have been discovered to be activated or enhanced. Apart from mechanical properties, the addition of W improves corrosion resistance as W helps to form a dense WO_(3) film on the alloy surface. Until now, despite the extensive studies in the literature, there is no available review paper focusing on the W doping of the f.c.c. HEAs. In that context, the effects of W doping on f.c.c. HEAs were reviewed in this work from three aspects, i.e., microstructure,mechanical property, and corrosion resistance. We expect this work can advance the application of the W alloying strategy in the f.c.c. HEAs.展开更多
This review summarizes the strengthening mechanisms of reduced activation ferritic/martensitic(RAFM)steels.High-angle grain boundaries,subgrain boundaries,nano-sized M_(23)C_(6),and MX carbide precipitates effectively...This review summarizes the strengthening mechanisms of reduced activation ferritic/martensitic(RAFM)steels.High-angle grain boundaries,subgrain boundaries,nano-sized M_(23)C_(6),and MX carbide precipitates effectively hinder dislocation motion and increase high-temperature strength.M23C6 carbides are easily coarsened under high temperatures,thereby weakening their ability to block dislocations.Creep properties are improved through the reduction of M23C6 carbides.Thus,the loss of strength must be compensated by other strengthening mechanisms.This review also outlines the recent progress in the development of RAFM steels.Oxide dispersion-strengthened steels prevent M23C6 precipitation by reducing C content to increase creep life and introduce a high density of nano-sized oxide precipitates to offset the reduced strength.Severe plastic deformation methods can substantially refine subgrains and MX carbides in the steel.The thermal deformation strengthening of RAFM steels mainly relies on thermo-mechanical treatment to increase the MX carbide and subgrain boundaries.This procedure increases the creep life of TMT(thermo-mechanical treatment)9Cr-1W-0.06Ta steel by~20 times compared with those of F82H and Eurofer 97 steels under 550℃/260 MPa.展开更多
In this study, a p H-sensitive micelle self-assembled from poly(L-histidine) based triblock copolymers of poly(ethylene glycol)–poly(D,L-lactide)–poly(L-histidine)(mPEG-PLA-PHis) was prepared and used as the intrace...In this study, a p H-sensitive micelle self-assembled from poly(L-histidine) based triblock copolymers of poly(ethylene glycol)–poly(D,L-lactide)–poly(L-histidine)(mPEG-PLA-PHis) was prepared and used as the intracellular doxorubicin(Dox) delivery for cancer chemotherapy. Dox was loaded into the micelles by thin-film hydration method and a Box–Behnken design for three factors at three levels was used to optimize the preparations. The optimized mPEG-PLA-Phis/Dox micelles exhibited good encapsulation efficiency of 91.12%,a mean diameter of 45 nm and narrow size distribution with polydispersity index of 0.256.In vitro drug release studies demonstrated that Dox was released from the micelles in a p Hdependent manner. Furthermore, the cellular evaluation of Dox loaded micelles displayed that the micelles possessed high antitumor activity in vitro with an IC50 of 35.30 μg/ml against MCF-7/ADR cells. The confocal microscopy and flow cytometry experiments indicated that m PEG-PLA-Phis micelles mediated efficient cytoplasmic delivery of Dox with the aid of poly(Lhistidine) mediated endosomal escape. In addition, blank m PEG-PLA-Phis micelles were shown to be nontoxic to MCF-7/ADR cells even at a high concentration of 200 μg/ml. The pHsensitive mPEG-PLA-PHis micelles have been demonstrated to be a promising nanosystem for the intracellular delivery of Dox for MDR reversal.展开更多
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...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.展开更多
Brittleness is a bottleneck hindering the applications of fruitful functional properties of Ni–Mn-based multiferroic alloys.Recently,experimental studies on B alloying shed new light on this issue.However,the knowled...Brittleness is a bottleneck hindering the applications of fruitful functional properties of Ni–Mn-based multiferroic alloys.Recently,experimental studies on B alloying shed new light on this issue.However,the knowledge related to B alloying is limited until now.More importantly,the mechanism of the improved ductility,which is intrinsically related to the chemical bond that is difficult to reveal by routine experiments,is still unclear.In this context,by first-principles calculations,the impact and the correlated mechanism of B alloying were systemically studied by investigating four alloying systems,i.e.,(Ni_(2-x)B_(x))MnGa,Ni_(2)(Mn_(1-x)B_(x))Ga,Ni_(2)Mn(Ga_(1-x)B_(x))and(Ni_(2)MnGa)_(1-x)B_(x).Results show that B prefers the direct occupation manner when it replaces Ni,Mn and Ga.For interstitial doping,B tends to locate at octahedral rather than tetrahedral interstice.Calculations show that the replacement of B for Ga can effectively improve(reduce)the inherent ductility(inherent strength)due to the weaker covalent strength of Ni(Mn)–B compared with Ni(Mn)–Ga.In contrast,B staying at octahedral interstice will lead to the formation of new chemical bonds between Ni(Mn)and B,bringing about a significantly improved strength and a greatly reduced ductility.Upon the substitutions for Ni and Mn,they affect both the inherent ductility and strength insignificantly.For phase transition,the replacement of B for Ga tends to destabilize the austenite,which can be understood in the picture of the band Jahn–Teller effect.Besides,the substitution for Ga would not lead to an obvious reduction of magnetization.展开更多
Evaluation of the stoichiometry of base cations(BCs,including K^(+),Na^(+),Ca^(2+),and Mg^(2+))and silicon(Si)(BCs:Si)during soil mineral weathering is essential to accurately quantify soil acidification rates.The aim...Evaluation of the stoichiometry of base cations(BCs,including K^(+),Na^(+),Ca^(2+),and Mg^(2+))and silicon(Si)(BCs:Si)during soil mineral weathering is essential to accurately quantify soil acidification rates.The aim of this study was to explore the differences and influencing factors of BCs:Si values of different soil genetic horizons in a deep soil profile derived from granite with different extents of mineral weathering.Soil type was typic acidi-udic Argosol.Soil samples were collected from Guangzhou,China,which is located in a subtropical region.To ensure that the BCs and Si originated from the mineral weathering process,soil exchangeable BCs were washed with an elution treatment.The BCs:Si values during weathering were obtained through a simulated acid rain leaching experiment using the batch method.Results showed that soil physical,chemical,and mineralogical properties varied from the surface horizon to saprolite in the soil profile.The BCs:Si values of soil genetic horizons during weathering were 0.3–3.7.The BCs:Si value was 1.7 in the surface horizon(A),1.1–3.7 in the argillic horizon(Bt),and 0.3–0.4 in the cambic(Bw)and transition(BC)horizons,as well as in horizon C(saprolite).The general pattern of BCs:Si values in the different horizons was as follows:Bt>A>Bw,BC,and C.Although BCs:Si values were influenced by weathering intensity,they did not correlate with the chemical index of alteration(CIA).The release amounts of Si and BCs are the joined impact of soil mineral composition and physical and chemical properties.A comprehensive analysis showed that the BCs:Si values of the soil derived from granite in this study were a combined result of the following factors:soil clay,feldspar,kaolinite,organic matter,pH,and CIA.The main controlling factors of BCs:Si in soils of different parent material types require extensive research.The wide variance of BCs:Si values in the deep soil profile indicated that H+consumed by soil mineral weathering was very dissimilar in the soils with different weathering intensities derived from the same parent material.Therefore,the estimation of the soil acidification rate based on H+biogeochemistry should consider the specific BCs:Si value.展开更多
We design high entropy alloys(HEAs) with different induction elements(Si/Al/Sn).In order to keep the crystal structure invariant and to investigate how the increment in saturation magnetization(Ms)is caused only by th...We design high entropy alloys(HEAs) with different induction elements(Si/Al/Sn).In order to keep the crystal structure invariant and to investigate how the increment in saturation magnetization(Ms)is caused only by the change of electron spin state,each set of HEAs contains a different amount of Mn.Synergistic effects among induction elements that induce the magnetic transformation of Mn from anti-ferromagnetism to ferromagnetism are found.Ms of added Mn reduces when a particular induction element(Si_(0.4)/Al_(0.4)/Sn_(0.4)) exists,while a larger increment of Ms appears when two induction elements coexist,Si_(0.4)Al_(0.4)(25.79 emu/g) and Sn_(0.4)Al_(0.4)(15.43 emu/g).This is reflected in the microcosmic magnetic structure for the emergence of closed domains due to large demagnetization energy,which is confirmed by the Lorentz transmission electron microscope(LTEM) data.The calculated magnetic moments and the exchange integral constants from density functional theory based on the Exact Muffin-Tin Orbits fo rmalism reveal that the magnetic state and the strength of fe rromagnetic and anti-ferromagnetic coupling determine the variation of Ms in different chemical environments.The difference in energy levels of coexisting multiple induction elements also leads to a larger increment of Ms,Si_(0.4)Al_(0.4)Sn_(0.4)(29.78 emu/g),and Si_(0.4)Al_(0.4)Ge_(0.4)Sn_(0.4)(31.00 emu/g).展开更多
Mechanical properties of high-entropy alloys(HEAs)with the face-centered cubic(fcc)structure strongly depend on their initial grain orientations.However,the orientation-dependent mechanical responses and the underlyin...Mechanical properties of high-entropy alloys(HEAs)with the face-centered cubic(fcc)structure strongly depend on their initial grain orientations.However,the orientation-dependent mechanical responses and the underlying plastic fl ow mechanisms of such alloys are not yet well understood.Here,deformation of the equiatomic FeMnCoCrNi HEA with various initial orientations under uniaxial tensile testing has been studied by using atomistic simulations,showing the results consistent with the recent experiments on fcc HEAs.The quantitative analysis of the activated deformation modes shows that the initiation of stacking faults is the main plastic deformation mechanism for the crystals initially oriented with[001],[111],and[112],and the total dislocation densities in these crystals are higher than that with the[110]and[123]orientations.Stacking faults,twinning,and hcp-martensitic transformation jointly promote the plastic deformation of the[110]orientation,and twinning in this crystal is more significant than that with other orientations.Deformation in the crystal oriented with[123]is dominated by the hcp-martensite transformation.Comparison of the mechanical behaviors in the FeMnCoCrNi alloy and the conventional materials,i.e.Cu and Fe50Ni50,has shown that dislocation slip tends to be activated more readily in the HEA.This is attributed to the larger lattice distortion in the HEA than the low-entropy materials,leading to the lower critical stress for dislocation nucleation and elastic–plastic transition in the former.In addition,the FeMnCoCrNi HEA with the larger lattice distortion leads to an enhanced capacity of storing dislocations.However,for the[001]-oriented HEA in which dislocation slip and stacking fault are the dominant deformation mechanisms,the limited deformation modes activated are insu fficient to improve the work hardening ability of the material.展开更多
This paper presents the design optimization of a self-circulated ventilation system for an enclosed permanent magnet(PM)traction motor utilized in the propulsion systems for subway trains.In order to analyze accuratel...This paper presents the design optimization of a self-circulated ventilation system for an enclosed permanent magnet(PM)traction motor utilized in the propulsion systems for subway trains.In order to analyze accurately the machine's inherent cooling capacity when the train is running,the ambient airflow and the related heat transfer coefficient(HTC)are numerically investigated considering synchronously the bogie installation structure.The machine is preliminary cooled with air ducts set on the motor shell,and the fluidic-thermal field distributions with only the shell air duct cooling are numerically calculated.During simulations,the HTC obtained in the former steps is applied to the external surface of the machine to model the inherent cooling characteristic caused by the train movement.To reduce the temperature rise and thus guarantee the motor's working reliability,an internal self-circulated air cooling system is proposed according to the machine temperature distribution.The air enclosed in the end-caps is driven by the blades mounted on both sides of the rotor core and forms two air circuits to bring the excessive power losses generated in the heating components to cool regions.The fluid flow and temperature rise distributions of the cooling system's structural parameters are further improved by the Taguchi method in order to confirm the efficacy of the internal air cooling system.展开更多
A large adiabatic temperature change(△T_(ad))is a prerequisite for the application of elastocaloric refriger-ation.Theoretically,a large volume change ratio(△V/V_(0))during martensitic transformation is favorable to...A large adiabatic temperature change(△T_(ad))is a prerequisite for the application of elastocaloric refriger-ation.Theoretically,a large volume change ratio(△V/V_(0))during martensitic transformation is favorable to enhance△T_(ad).However,the design or prediction of△V/V_(0)in experiments is a complex task because the structure of martensite changes simultaneously when the lattice parameter of austenite is tuned by mod-ifying chemical composition.So far,the solid strategy to tailor△V/V_(0)is still urgently desirable.In this work,a first-principles-based method was proposed to estimate△V/V_(0)for Ni-Mn-based alloys.With this method,the substitution of Ga for In is found to be an effective method to increase the value of△V/V_(0)for Ni-Mn-In alloys.Combined with the strategies of reducing the negative contribution of magnetic en-tropy change(via the substitution of Cu for Mn)and introducing strong crystallographic texture(through directional solidification),an outstanding elastocaloric prototype alloy of Ni_(50)(Mn_(28.5)Cu_(4.5))(In_(14)Ga_(3))was fabricated experimentally.At room temperature,a huge△T_(ad)of-19 K and a large specific adiabatic temperature change of 67.8 K/GPa are obtained.The proposed first-principle-assisted framework opens up the possibility of efficiently tailoring△V/V_(0)to promote the design of advanced elastocaloric refrigerants.展开更多
Brittleness is a critical issue hindering the potential application of the X_2YZ-type full Heusler alloys in several fields of state-of-the-art technologies.To realize optimization of brittleness or design a ductile H...Brittleness is a critical issue hindering the potential application of the X_2YZ-type full Heusler alloys in several fields of state-of-the-art technologies.To realize optimization of brittleness or design a ductile Heuser alloy,it is greatly urgent to identify the key materials factors deciding brittleness and establish an empirical rule to effectively evaluate ductility.For this purpose,by using a machine learning and human analysis cooperation approach,the brittleness of the X_2YZ-type Heusler alloys was systematically studied.Results showed that the ductility is majorly decided by 6 key materials factors in the studied alloys.Using these 6 factors,a machine learning model to predict the Pugh's ratio k was constructed.Further analyses showed that the crystal structure of the X component could be the most critical factor deciding the ductility.The X component has the face-centered cubic(FCC)structure for most of the alloys with superior ductility.To effectively estimate ductility and guide materials design,an empirical formula of k=mEWF_(m+n)G_(m)+k_(0)was established based on the known information of electron work function(EWF)and shear modulus(G)of the X,Y,and Z elements where the subscript m represents the weight-average value.The coefficients of m(negative)and n(positive)were confirmed to have opposite signs,which can be explained based on the relations between the ductility and the deformation/fracture resistance.This work is expected to deepen the understanding in ductility and promote the design of advanced ductile Heusler alloys.展开更多
By performing in situ neutron diffraction experiments on an austenitic-ferritic stainless steel subjected to lowcycle fatigue loading, the deformation heterogeneity of the material at microscopic level has been reveal...By performing in situ neutron diffraction experiments on an austenitic-ferritic stainless steel subjected to lowcycle fatigue loading, the deformation heterogeneity of the material at microscopic level has been revealed. Based on the in situ neutron diffraction data collected from a single specimen together with the mechanical properties learned from the ex situ micro-hardness, a correlation has been found. The performance versus diffraction-profile correlation agrees with the cyclic-deformation-induced dislocation evolution characterized by ex situ TEM observation. Moreover, based on the refined neutron diffraction-profile data, evident strain anisotropy is found in the austenite. The high anisotropy in this phase is induced by the increase in dislocation density and hence contributes to the hardening of the steel at the first 10 cycles.Beyond 10 fatigue cycles, the annihilation and the rearrangement of the dislocations in both austenitic and ferritic phases softens the plastically deformed specimen. The study suggests that the evolution of strain anisotropy among the differently oriented grains and micro-strain induced by lattice distortion in the respective phases mostly affect the cyclic-deformationinduced mechanical behavior of the steel at different stages of fatigue cycles. The stress discrepancy between phases is not the dominant mechanism for the deformation of the steel.展开更多
基金supported by the Natural Science Foundation of Hebei Province(E2024209052)the Youth Scholars Promotion Plan of North China University of Science and Technology(QNTJ202307).
文摘Eutectic high entropy alloys are noted for their excellent castability and comprehensive mechanical properties.The excellent mechanical properties are closely related to the activation and evolution of deformation mechanisms at the atomic scale.In this work,AlCoCrFeNi2.1 alloy is taken as the research object.The mechanical behaviors and deformation mechanisms of the FCC and B2 single crystals with different orientations and the FCC/B2 composites with K-S orientation relationship during nanoindentation processes are systematically studied by molecular dynamics simulations.The results show that the mechanical behaviors of FCC single crystals are significantly orientation-dependent,meanwhile,the indentation force of[110]single crystal is the lowest at the elastic-plastic transition point,and that for[100]single crystal is the lowest in plastic deformation stage.Compared with FCC,the stress for B2 single crystals at the elastic-plastic transition point is higher.However,more deformation systems such as stacking faults,twins and dislocation loops are activated in FCC single crystal during the plastic deformation process,resulting in higher indentation force.For composites,the flow stress increases with the increase of B2 phase thickness during the initial stage of deformation.When indenter penetrates heterogeneous interface,the significantly increased deformation system in FCC phase leads to a significant increase in indentation force.The mechanical behaviors and deformation mechanisms depend on the component single crystal.When the thickness of the component layer is less than 15 nm,the heterogeneous interfaces fail to prevent the dislocation slip and improve the indentation force.The results will enrich the plastic deformation mechanisms of multi-principal eutectic alloys and provide guidance for the design of nanocrystalline metallic materials.
基金sponsored by Natural Science Foundation of Shaanxi Province (2020JZ-23)the Fundamental Research Funds for the Central Universities (GK201901002, GK201701007 and GK201902014)the 111 Project (B14041)。
文摘Recently, the surface chemical functionalization and morphology control of precious metal nanostructures have been recognized as two efficient strategies for improving their electroactivity and/or selectivity. In this work, 1, 10-phenanthroline monohydrate(PM) functionalized Pt nanodendrites(Pt-NDs) on carbon cloth(CC)(denoted as PM@Pt-NDs/CC) and polyethylenimine(PEI) functionalized Pt-NDs on CC(denoted as PEI@Pt-NDs/CC) are successfully achieved by immersing Pt-NDs/CC into PM and PEI aqueous solutions, respectively. PEI functionalization of Pt-NDs/CC improves its electroactivity for hydrogen evolution reaction(HER) due to local proton enrichment whereas PM functionalization of Pt-NDs/CC improves its electroactivity for formic acid oxidation reaction(FAOR) by facilitating dehydrogenation pathway. With such high activity, a two-electrode electrolyzer is assembled using PM@Pt-NDs/CC as the anodic electrocatalyst and PEI@Pt-NDs/CC as the cathodic electrocatalyst for electrochemical reforming of formic acid, which only requires 0.45 V voltage to achieve the current density of 10 mA cm^(-1) for highpurity hydrogen production, much lower than conventional water electrolysis(1.59 V). The work presents an example of interfacial engineering enhancing electrocatalytic activity and indicates that electrochemical reforming of formic acid is an energy-saving electrochemical method for high-purity hydrogen production.
基金financially supported by the National Natural Science of Foundation of China(No.52371097)the Shenyang Unveiling and Leading Project,China(No.22-301-1-01)。
文摘The wave-absorbing materials are kinds of special electromagnetic functional materials and have been widely used in electromagnetic pollution control and military fields.In-situ integrated hierarchical structure construction is thought as a promising route to improve the microwave absorption performance of the materials.In the present work,layer-structured Co-metal-organic frameworks(Co-MOFs)precursors were grown in-situ on the surface of carbon fibers with the hydrothermal method.After annealed at 500℃ under Ar atmosphere,a novel multiscale hierarchical composite(Co@C/CF)was obtained with the support of carbon fibers,keeping the flower-like structure.Scanning electron microscope,transmission electron microscope,X-ray diffraction,Raman,and X-ray photoelectron spectroscopy were performed to analyze the microstructure and composition of the hierarchical structure,and the microwave absorption performance of the Co@C/CF composites were investigated.The results showed that the growth of the flower-like structure on the surface of carbon fiber was closely related to the metal-to-ligand ratio.The optimized Co@C/CF flower-like composites achieved the best reflection loss of−55.7 dB in the low frequency band of 6–8 GHz at the thickness of 2.8 mm,with the corresponding effective absorption bandwidth(EAB)of 2.1 GHz.The EAB of 3.24 GHz was achieved in the high frequency range of 12–16 GHz when the thickness was 1.5 mm.The excellent microwave absorption performance was ascribed to the introduction of magnetic components and the construction of the unique structure.The flower-like structure not only balanced the impedance of the fibers themselves,but also extended the propagation path of the microwave and then increased the multiple reflection losses.This work provides a convenient method for the design and development of wave-absorbing composites with in-situ integrated structure.
基金supported by the National Key Research and Development Program of China(No.2021YFA1200203)the National Natural Science Foundation of China(Nos.52371097,51922026,and 52301136).
文摘Compositionally-complex alloys(CCAs)with the face-centered cubic(fcc)structure exhibit excellent frac-ture toughness and stable mechanical property across a broad temperature range from cryogenic to room temperatures.However,yield strength of those alloys is usually low,making them difficult to meet the demands of practical engineering application.In a prototype CCA with the nominal chemical composition of Co10Cr10Fe49Mn30N1(atom percent),a multi-scaled heterostructure from sample to atomic scales was obtained by performing triaxial cyclic compression and short-term annealing on the blocky alloy.The ma-terial exhibits a heterogeneous distribution of strain at the sample scale.At the grain scale,dense twins and twin-twin network,laths featured with local chemical order as well as dislocation cells jointly hinder plastic deformation.At the nanoscale,the chemical order within grains also impedes dislocation motion.During plastic deformation,different sample positions within the heterogeneous material and various regions at each position undergo coordinated deformation,resulting in significant hetero-deformation in-duced strengthening.Simultaneously,the continuously activated dislocations,stacking faults and nano-twins lead to a high yield strength of 1020 MPa in the material while maintaining a fracture elongation of 30%.This study provides new insights for the design and development of high-performance metallic materials.
基金financially supported by the National Natural Science Foundation of China(No.51571057)the Fundamental Research Funds for the Central Universities(No.N170204012)
文摘Ti/Cu multilayered composites were fabricated via accumulative roll bonding(ARB). During codeformation of the constituent metals, the hard Ti layers necked preferentially and then fragmented with the development of shear bands. Transmission electron microscopy showed that with increasing ARB cycles, grains in Ti were significantly refined even though dynamic recrystallization has occurred. For Cu the significant grain refinement was only found within the shear banded region when the composite was processed after five ARB cycles. Due to the diffusion of Cu atoms into Ti at the heterophase interfaces, amorphization with a width less than 10 nm was identified even in the composite processed by one cycle. At higher ARB cycles, the width of amorphous region increased and intermetallic compounds CuTi appeared from the region. The lattice defects introduced at the heterophase interfaces under roll bonding was responsible for the formation of the nano-scaled compounds. X-ray diffraction showed that an abnormal {1120} fiber texture was developed in Ti layers, while significant brass-type textures were developed in Cu layers. Some orientations along the {1120} fiber favored the prismatic < a> slip for Ti.Tensile tests revealed the elevated strength without a substantial sacrifice of ductility in the composites during ARB. The unique mechanical properties were attributed to the significantly refined grains in individual metals, the good bonding between the constituent metals, as well as the development of an abnormal {1120} fiber texture in Ti layers.
基金financially supported by the National Natural Science Foundation of China(No.51922026)the Fundamental Research Funds for the Central Universities(Nos.N2002005 and N2007011)+1 种基金the Liaoning Natural Science Foundation(No.20180510010)the“111 Project”(No.B20029)。
文摘High-entropy alloys(HEAs)have attracted great research interest owing to their good combination of high strength and ductility at both room and cryogenic temperatures.However,expensive raw materials are always added to overcome the strength-ductility trade-off at low temperatures,leading to an increased production cost for the cryogenically used alloys.In this work,a series of nitrogen-doped Fe Mn Co Cr HEAs have been processed by homogenization annealing,cold rolling and recrystallization annealing followed by water quenching.The microstructural evolution and mechanical properties of the alloys are studied systematically.The Fe_(49)Mn_(30)Co_(10)Cr_(10)N1alloy shows excellent mechanical properties at both 293 K and 77 K.Particularly,the yield and ultimate tensile strength of 1078 and 1630 MPa are achieved at the cryogenic temperature,respectively,while a satisfactory uniform elongation of 33.5%is maintained.The ultrahigh yield strength results from the microstructure refinement caused by the activation of athermal martensitic transformation and mechanical twinning that occur in the elastic regime together with the increased lattice friction due to the cryogenic environment.In the plastic regime,the dynamic Hall-Petch effect caused by twinning,martensitic transformation,and reverse transformation together with the high barrier to dislocation motion jointly contribute to the ultrahigh tensile strength.Simultaneously,the transformation induced plasticity(TRIP)and the twinning induced plasticity(TWIP)effects jointly contribute to the ductility.The design strategy for attaining superior mechanical properties at low temperatures,i.e.by adjusting stacking fault energy in the interstitial metastable HEAs,guides the development of high-performance and low-cost alloys for cryogenic applications.
基金financially supported by the National Key R&D Program of China (No.2021YFA1200203)the National Natural Science Foundation of China (Nos.51922026 and 51975111)+1 种基金the Fundamental Research Funds for the Central Universities (No.N2202015,N2002005,and N2105001)the 111 Project of China (No.BP0719037 and B20029)。
文摘Face-centered cubic (f.c.c.) high entropy alloys (HEAs) are attracting more and more attention owing to their excellent strength and ductility synergy, irradiation resistance, etc. However, the yield strength of f.c.c. HEAs is generally low, significantly limiting their practical applications. Recently, the alloying of W has been evidenced to be able to remarkably improve the mechanical properties of f.c.c. HEAs and is becoming a hot topic in the community of HEAs. To date, when W is introduced, multiple strengthening mechanisms, including solid-solution strengthening, precipitation strengthening (μphase,σphase, and b.c.c. phase), and grain-refinement strengthening, have been discovered to be activated or enhanced. Apart from mechanical properties, the addition of W improves corrosion resistance as W helps to form a dense WO_(3) film on the alloy surface. Until now, despite the extensive studies in the literature, there is no available review paper focusing on the W doping of the f.c.c. HEAs. In that context, the effects of W doping on f.c.c. HEAs were reviewed in this work from three aspects, i.e., microstructure,mechanical property, and corrosion resistance. We expect this work can advance the application of the W alloying strategy in the f.c.c. HEAs.
基金the National Key Research and Development Program of China(No.2016YFB 0300600)the National Natural Science Foundation of China(NSFC)(No.51922026)+1 种基金the Fundamental Research Funds for the Central Universities(Nos.N2002013,N2002005,N2007011)the 111 Project(No.B20029).
文摘This review summarizes the strengthening mechanisms of reduced activation ferritic/martensitic(RAFM)steels.High-angle grain boundaries,subgrain boundaries,nano-sized M_(23)C_(6),and MX carbide precipitates effectively hinder dislocation motion and increase high-temperature strength.M23C6 carbides are easily coarsened under high temperatures,thereby weakening their ability to block dislocations.Creep properties are improved through the reduction of M23C6 carbides.Thus,the loss of strength must be compensated by other strengthening mechanisms.This review also outlines the recent progress in the development of RAFM steels.Oxide dispersion-strengthened steels prevent M23C6 precipitation by reducing C content to increase creep life and introduce a high density of nano-sized oxide precipitates to offset the reduced strength.Severe plastic deformation methods can substantially refine subgrains and MX carbides in the steel.The thermal deformation strengthening of RAFM steels mainly relies on thermo-mechanical treatment to increase the MX carbide and subgrain boundaries.This procedure increases the creep life of TMT(thermo-mechanical treatment)9Cr-1W-0.06Ta steel by~20 times compared with those of F82H and Eurofer 97 steels under 550℃/260 MPa.
文摘In this study, a p H-sensitive micelle self-assembled from poly(L-histidine) based triblock copolymers of poly(ethylene glycol)–poly(D,L-lactide)–poly(L-histidine)(mPEG-PLA-PHis) was prepared and used as the intracellular doxorubicin(Dox) delivery for cancer chemotherapy. Dox was loaded into the micelles by thin-film hydration method and a Box–Behnken design for three factors at three levels was used to optimize the preparations. The optimized mPEG-PLA-Phis/Dox micelles exhibited good encapsulation efficiency of 91.12%,a mean diameter of 45 nm and narrow size distribution with polydispersity index of 0.256.In vitro drug release studies demonstrated that Dox was released from the micelles in a p Hdependent manner. Furthermore, the cellular evaluation of Dox loaded micelles displayed that the micelles possessed high antitumor activity in vitro with an IC50 of 35.30 μg/ml against MCF-7/ADR cells. The confocal microscopy and flow cytometry experiments indicated that m PEG-PLA-Phis micelles mediated efficient cytoplasmic delivery of Dox with the aid of poly(Lhistidine) mediated endosomal escape. In addition, blank m PEG-PLA-Phis micelles were shown to be nontoxic to MCF-7/ADR cells even at a high concentration of 200 μg/ml. The pHsensitive mPEG-PLA-PHis micelles have been demonstrated to be a promising nanosystem for the intracellular delivery of Dox for MDR reversal.
基金the financial support of the National Natural Science Foundation of China(Grant No.51101030)the Fundamental Research Funds for the Central Universities(Grant No.N100702001)
文摘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.
基金the National Natural Science Foundation of China(Grant No.51801020,51922026,51771044)the Fundamental Research Funds for the Central Universities(Grant No.N2002005,N2002021)+2 种基金the Liao Ning Revitalization Talents Program(Grant No.XLYC1802023)the Ph.D.Starting Foundation of Liaoning Province(Grant No.20180540115)Programme of Introducing Talents of Discipline Innovation to Universities(the 111 Project of China,No.BP0719037,B20029)。
文摘Brittleness is a bottleneck hindering the applications of fruitful functional properties of Ni–Mn-based multiferroic alloys.Recently,experimental studies on B alloying shed new light on this issue.However,the knowledge related to B alloying is limited until now.More importantly,the mechanism of the improved ductility,which is intrinsically related to the chemical bond that is difficult to reveal by routine experiments,is still unclear.In this context,by first-principles calculations,the impact and the correlated mechanism of B alloying were systemically studied by investigating four alloying systems,i.e.,(Ni_(2-x)B_(x))MnGa,Ni_(2)(Mn_(1-x)B_(x))Ga,Ni_(2)Mn(Ga_(1-x)B_(x))and(Ni_(2)MnGa)_(1-x)B_(x).Results show that B prefers the direct occupation manner when it replaces Ni,Mn and Ga.For interstitial doping,B tends to locate at octahedral rather than tetrahedral interstice.Calculations show that the replacement of B for Ga can effectively improve(reduce)the inherent ductility(inherent strength)due to the weaker covalent strength of Ni(Mn)–B compared with Ni(Mn)–Ga.In contrast,B staying at octahedral interstice will lead to the formation of new chemical bonds between Ni(Mn)and B,bringing about a significantly improved strength and a greatly reduced ductility.Upon the substitutions for Ni and Mn,they affect both the inherent ductility and strength insignificantly.For phase transition,the replacement of B for Ga tends to destabilize the austenite,which can be understood in the picture of the band Jahn–Teller effect.Besides,the substitution for Ga would not lead to an obvious reduction of magnetization.
基金supported by the National Natural Science Foundation of China(Nos.41877010 and U1901601)。
文摘Evaluation of the stoichiometry of base cations(BCs,including K^(+),Na^(+),Ca^(2+),and Mg^(2+))and silicon(Si)(BCs:Si)during soil mineral weathering is essential to accurately quantify soil acidification rates.The aim of this study was to explore the differences and influencing factors of BCs:Si values of different soil genetic horizons in a deep soil profile derived from granite with different extents of mineral weathering.Soil type was typic acidi-udic Argosol.Soil samples were collected from Guangzhou,China,which is located in a subtropical region.To ensure that the BCs and Si originated from the mineral weathering process,soil exchangeable BCs were washed with an elution treatment.The BCs:Si values during weathering were obtained through a simulated acid rain leaching experiment using the batch method.Results showed that soil physical,chemical,and mineralogical properties varied from the surface horizon to saprolite in the soil profile.The BCs:Si values of soil genetic horizons during weathering were 0.3–3.7.The BCs:Si value was 1.7 in the surface horizon(A),1.1–3.7 in the argillic horizon(Bt),and 0.3–0.4 in the cambic(Bw)and transition(BC)horizons,as well as in horizon C(saprolite).The general pattern of BCs:Si values in the different horizons was as follows:Bt>A>Bw,BC,and C.Although BCs:Si values were influenced by weathering intensity,they did not correlate with the chemical index of alteration(CIA).The release amounts of Si and BCs are the joined impact of soil mineral composition and physical and chemical properties.A comprehensive analysis showed that the BCs:Si values of the soil derived from granite in this study were a combined result of the following factors:soil clay,feldspar,kaolinite,organic matter,pH,and CIA.The main controlling factors of BCs:Si in soils of different parent material types require extensive research.The wide variance of BCs:Si values in the deep soil profile indicated that H+consumed by soil mineral weathering was very dissimilar in the soils with different weathering intensities derived from the same parent material.Therefore,the estimation of the soil acidification rate based on H+biogeochemistry should consider the specific BCs:Si value.
基金supported financially by the Program for the National Key R&D Program of China (No.2017YFB0703103)the National Natural Science Foundation of China (Nos.51577021 and U1704253)+1 种基金the Fundamental Research Funds for the Central Universities (DUT17GF107)the Swedish Foundation for Strategic Research。
文摘We design high entropy alloys(HEAs) with different induction elements(Si/Al/Sn).In order to keep the crystal structure invariant and to investigate how the increment in saturation magnetization(Ms)is caused only by the change of electron spin state,each set of HEAs contains a different amount of Mn.Synergistic effects among induction elements that induce the magnetic transformation of Mn from anti-ferromagnetism to ferromagnetism are found.Ms of added Mn reduces when a particular induction element(Si_(0.4)/Al_(0.4)/Sn_(0.4)) exists,while a larger increment of Ms appears when two induction elements coexist,Si_(0.4)Al_(0.4)(25.79 emu/g) and Sn_(0.4)Al_(0.4)(15.43 emu/g).This is reflected in the microcosmic magnetic structure for the emergence of closed domains due to large demagnetization energy,which is confirmed by the Lorentz transmission electron microscope(LTEM) data.The calculated magnetic moments and the exchange integral constants from density functional theory based on the Exact Muffin-Tin Orbits fo rmalism reveal that the magnetic state and the strength of fe rromagnetic and anti-ferromagnetic coupling determine the variation of Ms in different chemical environments.The difference in energy levels of coexisting multiple induction elements also leads to a larger increment of Ms,Si_(0.4)Al_(0.4)Sn_(0.4)(29.78 emu/g),and Si_(0.4)Al_(0.4)Ge_(0.4)Sn_(0.4)(31.00 emu/g).
基金financially supported by the National Natural Science Foundation of China(No.51922026)the Fundamental Research Funds for the Central Universities(Nos.N2002005 and N2007011)+1 种基金the Liaoning Natural Science Foundation(No.20180510010)the 111 Project(No.B20029)。
文摘Mechanical properties of high-entropy alloys(HEAs)with the face-centered cubic(fcc)structure strongly depend on their initial grain orientations.However,the orientation-dependent mechanical responses and the underlying plastic fl ow mechanisms of such alloys are not yet well understood.Here,deformation of the equiatomic FeMnCoCrNi HEA with various initial orientations under uniaxial tensile testing has been studied by using atomistic simulations,showing the results consistent with the recent experiments on fcc HEAs.The quantitative analysis of the activated deformation modes shows that the initiation of stacking faults is the main plastic deformation mechanism for the crystals initially oriented with[001],[111],and[112],and the total dislocation densities in these crystals are higher than that with the[110]and[123]orientations.Stacking faults,twinning,and hcp-martensitic transformation jointly promote the plastic deformation of the[110]orientation,and twinning in this crystal is more significant than that with other orientations.Deformation in the crystal oriented with[123]is dominated by the hcp-martensite transformation.Comparison of the mechanical behaviors in the FeMnCoCrNi alloy and the conventional materials,i.e.Cu and Fe50Ni50,has shown that dislocation slip tends to be activated more readily in the HEA.This is attributed to the larger lattice distortion in the HEA than the low-entropy materials,leading to the lower critical stress for dislocation nucleation and elastic–plastic transition in the former.In addition,the FeMnCoCrNi HEA with the larger lattice distortion leads to an enhanced capacity of storing dislocations.However,for the[001]-oriented HEA in which dislocation slip and stacking fault are the dominant deformation mechanisms,the limited deformation modes activated are insu fficient to improve the work hardening ability of the material.
基金supported by the National Natural Science Foundation of China under Grant 52107007the China Scholarship Council under Grant 202008120084the“Chunhui Plan”Collaborative Research Project of Chinese Ministry of Education under Grant HZKY20220604。
文摘This paper presents the design optimization of a self-circulated ventilation system for an enclosed permanent magnet(PM)traction motor utilized in the propulsion systems for subway trains.In order to analyze accurately the machine's inherent cooling capacity when the train is running,the ambient airflow and the related heat transfer coefficient(HTC)are numerically investigated considering synchronously the bogie installation structure.The machine is preliminary cooled with air ducts set on the motor shell,and the fluidic-thermal field distributions with only the shell air duct cooling are numerically calculated.During simulations,the HTC obtained in the former steps is applied to the external surface of the machine to model the inherent cooling characteristic caused by the train movement.To reduce the temperature rise and thus guarantee the motor's working reliability,an internal self-circulated air cooling system is proposed according to the machine temperature distribution.The air enclosed in the end-caps is driven by the blades mounted on both sides of the rotor core and forms two air circuits to bring the excessive power losses generated in the heating components to cool regions.The fluid flow and temperature rise distributions of the cooling system's structural parameters are further improved by the Taguchi method in order to confirm the efficacy of the internal air cooling system.
基金supported by the National Natural Science Foundation of China(Nos.51922026,51975111)the Fundamental Research Funds for the Central Universities(Nos.N2202015,N2230002,N2002021,N2105001)the 111 Project of China(Nos.BP0719037,B20029).
文摘A large adiabatic temperature change(△T_(ad))is a prerequisite for the application of elastocaloric refriger-ation.Theoretically,a large volume change ratio(△V/V_(0))during martensitic transformation is favorable to enhance△T_(ad).However,the design or prediction of△V/V_(0)in experiments is a complex task because the structure of martensite changes simultaneously when the lattice parameter of austenite is tuned by mod-ifying chemical composition.So far,the solid strategy to tailor△V/V_(0)is still urgently desirable.In this work,a first-principles-based method was proposed to estimate△V/V_(0)for Ni-Mn-based alloys.With this method,the substitution of Ga for In is found to be an effective method to increase the value of△V/V_(0)for Ni-Mn-In alloys.Combined with the strategies of reducing the negative contribution of magnetic en-tropy change(via the substitution of Cu for Mn)and introducing strong crystallographic texture(through directional solidification),an outstanding elastocaloric prototype alloy of Ni_(50)(Mn_(28.5)Cu_(4.5))(In_(14)Ga_(3))was fabricated experimentally.At room temperature,a huge△T_(ad)of-19 K and a large specific adiabatic temperature change of 67.8 K/GPa are obtained.The proposed first-principle-assisted framework opens up the possibility of efficiently tailoring△V/V_(0)to promote the design of advanced elastocaloric refrigerants.
基金financially supported by the National Natural Science Foundation of China(Nos.51801020,51922026,51975111)the Fundamental Research Funds for the Central Universities(Nos.N2002005,N2105001)the 111 Project of China(Nos.BP0719037,B20029)。
文摘Brittleness is a critical issue hindering the potential application of the X_2YZ-type full Heusler alloys in several fields of state-of-the-art technologies.To realize optimization of brittleness or design a ductile Heuser alloy,it is greatly urgent to identify the key materials factors deciding brittleness and establish an empirical rule to effectively evaluate ductility.For this purpose,by using a machine learning and human analysis cooperation approach,the brittleness of the X_2YZ-type Heusler alloys was systematically studied.Results showed that the ductility is majorly decided by 6 key materials factors in the studied alloys.Using these 6 factors,a machine learning model to predict the Pugh's ratio k was constructed.Further analyses showed that the crystal structure of the X component could be the most critical factor deciding the ductility.The X component has the face-centered cubic(FCC)structure for most of the alloys with superior ductility.To effectively estimate ductility and guide materials design,an empirical formula of k=mEWF_(m+n)G_(m)+k_(0)was established based on the known information of electron work function(EWF)and shear modulus(G)of the X,Y,and Z elements where the subscript m represents the weight-average value.The coefficients of m(negative)and n(positive)were confirmed to have opposite signs,which can be explained based on the relations between the ductility and the deformation/fracture resistance.This work is expected to deepen the understanding in ductility and promote the design of advanced ductile Heusler alloys.
基金the financial support of the Fundamental Research Funds for the Central Universities(Nos.N130510001 and L1502029)the Program for New Century Excellent Talents in University(No.NCET-13-0104)the National Natural Science Foundation of China(Nos.51202256,51201027)
文摘By performing in situ neutron diffraction experiments on an austenitic-ferritic stainless steel subjected to lowcycle fatigue loading, the deformation heterogeneity of the material at microscopic level has been revealed. Based on the in situ neutron diffraction data collected from a single specimen together with the mechanical properties learned from the ex situ micro-hardness, a correlation has been found. The performance versus diffraction-profile correlation agrees with the cyclic-deformation-induced dislocation evolution characterized by ex situ TEM observation. Moreover, based on the refined neutron diffraction-profile data, evident strain anisotropy is found in the austenite. The high anisotropy in this phase is induced by the increase in dislocation density and hence contributes to the hardening of the steel at the first 10 cycles.Beyond 10 fatigue cycles, the annihilation and the rearrangement of the dislocations in both austenitic and ferritic phases softens the plastically deformed specimen. The study suggests that the evolution of strain anisotropy among the differently oriented grains and micro-strain induced by lattice distortion in the respective phases mostly affect the cyclic-deformationinduced mechanical behavior of the steel at different stages of fatigue cycles. The stress discrepancy between phases is not the dominant mechanism for the deformation of the steel.
