查看更多>>摘要：Continuous cooling transformation diagrams in synthetic weld heat-affected zone(SH-CCT diagrams)show the phase transition temperature and hardness at different cooling rates,which is an important basis for formulating the welding process or predicting the performance of welding heat-affected zone.However,the experimental determination of SH-CCT diagrams is a time-consuming and costly process,which does not conform to the development trend of new materials.In addition,the prediction of SH-CCT diagrams using metallurgical models remains a challenge due to the complexity of alloying elements and welding processes.So,in this study,a hybrid machine learning model consisting of multilayer per-ceptron classifier,k-Nearest Neighbors and random forest is established to predict the phase transforma-tion temperature and hardness of low alloy steel using chemical composition and cooling rate.Then the SH-CCT diagrams of 6 kinds of steels are calculated by the hybrid machine learning model.The results show that the accuracy of the classification model is up to 100％,the predicted values of the regression models are in good agreement with the experimental results,with high correlation coefficient and low error value.Moreover,the mathematical expressions of hardness in welding heat-affected zone of low alloy steel are calculated by symbolic regression,which can quantitatively express the relationship be-tween alloy composition,cooling time and hardness.This study demonstrates the great potential of the material informatics in the field of welding technology.
查看更多>>摘要：Isothermal oxidation behaviors of Ni-Fe(wt.％)and of the same alloy with additions of 10 and 15％Cr al-loys in the air at 800℃and 900℃and their anodic behaviors in aluminum electrolysis system at 800℃were evaluated.The composition morphologies of oxide scales were characterized by XRD,SEM,and EDS.Results show that the scales formed on Ni-Fe alloy at both temperatures consisted of an inner(Ni,Fe)3O4 layer and an outer Fe2O3 layer.For Ni-Fe-10Cr alloy,an external(Ni,Fe)3O4/Fe2O3 layers and an internal oxidation zone were formed at 800℃,while a continuous Cr2O3 layer forms at the internal oxidation zone/substrate interface at 900℃.A multilayer structure oxide of Cr2O3/(Ni,Fe,Cr)3O4/(Ni,Fe)3O4/Fe2O3 was formed on Ni-Fe-15Cr alloy at 800℃,while at 900℃the Fe2O3 becomes discontinuous disperses in the(Ni,Fe)3O4 layer close to the surface.Increases in oxidation temperature or Cr content for Ni-Fe-Cr alloys promote the growth of the inner Cr2O3 layer and simultaneously reduce Fe2O3 content.After 4 h of electrolysis at an anode current density of 0.25 A cm-2,the oxidation resistance of Ni-Fe-15Cr anode is superior to the Ni-Fe anode.
查看更多>>摘要：Based on the general[Mo]equivalent criterion and d-electron orbital theory,a new ultrahigh-strength βtitanium alloy with eight major elements(Ti-4.5Al-6.5Mo-2Cr-2.6Nb-2Zr-2Sn-1V,TB17)for industrial ap-plications was developed.An ingot of five tons was successfully melted by thrice vacuum consumable arc melting.The microstructure and elements partitioning of different conditions were investigated system-atically.The results suggest that the hierarchical structures of micro-scale first α phase(αf),nano-scale secondary α phase(αs),and ultrafine FCC substructures can be tailored by solution plus aging(STA)heat treatment.The lateral and epitaxial growth of αf phase promotes the HCP-α to FCC substructure transfor-mation with the help of elements partitioning during the aging process.Moreover,the element V,gener-ally regarded as β stabilizer,is found to mainly concentrate in the Al-rich αf phase in this study probably due to its relatively lower content and the strong bonding energy of Al-V.The hierarchical structure has a strong interaction with dislocations,which contributes to achieve a superhigh strength of 1376 MPa.In addition,the plastic strain is partitioned in the multi-scale precipitates(such as the α and FCC sub-structures)and β matrix,resulting in a considerable plasticity.TEM observation demonstrates that high density entangled dislocations at interfaces and mechanical twins exist in the STA sample after tensile test.It can be deduced that both dislocation slipping and twinning mechanisms are present in this alloy.Therefore,TB17 alloy can serve as an excellent candidate for structural materials on aircrafts that require high strength and lightweight.
查看更多>>摘要：Twinning stress is known to be a critical factor for the actuating performance of magnetic shape mem-ory alloys because of the harmful deterioration of their magnetic field-induced strain effect.However,the intrinsic origin of the high twinning stress is still in debate.In this work,we firstly fill this gap by pre-cisely probing the reorientation behaviors of A-C and A-B two common macro-twin interfaces under the stimulus of uniaxial compression in-situ transmission electron microscope.The grain boundary is proved to be the main reason for large twinning stress.The twinning stress of the A-C and A-B type interfaces quantitatively are～0.69 and 1.27 MPa within the plate respectively.The A-C type interface evidently has smaller twinning stress and larger deformation variable than the A-B interface.Under the action of com-pression,not only the orientations of the crystals have changed,but also the roles of the major and minor lamellae have changed for both interfaces due to the movements of twinning dislocations.Combining in-situ and quasi in-situ electron diffraction data,the reorientation process is clearly and intuitively shown by the stereographic projection.Atomic models and the theory of dislocation motion are proposed to phenomenologically clarify the intrinsic mechanism.This work is believed to not only provide a deeper understanding of the deformation mechanism of magnetic shape memory alloys under uniaxial compres-sion testing,but also discover that compression training is not the mechanical training way to decrease the twinning stress of non-modulated martensite in single crystal shape memory alloys.
查看更多>>摘要：This study shows that the mechanical strength of the composite of Fe matrix and titanium carbide(TiC)ceramic particles is significantly enhanced with addition of molybdenum(Mo)atoms.TiC reinforced Fe(Fe-0.2C-7Mn)composites with and without Mo were fabricated by a liquid pressing infiltration(LPI)process and the effect of Mo on interfacial properties of TiC-Fe composite was investigated using atomic probe tomography(APT)analysis,molecular dynamics(MD)simulations,first-principle density functional theory(DFT),and thermodynamic calculations.First,DFT calculations showed that total energies of the Mo-doped TiC-Fe superlattices strongly depend on the position of Mo defects,and are minimized when the Mo atom is located at the TiC/Fe interface,supporting the probable formation of MoC-like interphase at the TiC/Fe interface region.Then,APT analysis confirmed the DFT predictions by finding that about 6.5 wt.％Mo is incorporated in the TiC-Fe(Mo)composite and that sub-micrometer thick(Ti,Mo)C in-terphase is indeed formed near the interface.The MD simulations show that Mo atoms migrate to the Mo-free TiC-Fe interface at elevated temperatures and the mechanical strength of the interface is consid-erably enhanced,which is in good agreement with experimental observations.
查看更多>>摘要：A novel high-entropy material,(Y0.2Gd0.2Er0.2Yb0.2Lu0.2)2Zr2O7 was successfully synthesized by the solid state reaction method and spark plasma sintering,and investigated as a promising thermal barrier coating material.Rare-earth elements were distributed homogeneously in the pyrochlore structure.It was found that the prepared high-entropy ceramic maintains pyrochlore structure at the temperature up to 1600℃,and it possesses a similar thermal expansion coefficient(10.2×10-6 K-1 at 25-900℃)to that of YSZ,low thermal conductivity(＜0.9 W m-1 K-1 at 100-1000℃)and good CMAS resistance(infiltration depth is 22 μm after annealed at 1300℃for 24 h).The corrosion process was investigated,and RE elements distributing homogeneously in(Y0.2Gd0.2Er0.2Yb0.2 Lu0.2)2Zr2O7 show different diffusion rates in CMAS.RE3+with a larger radius(closer to Ca2+)is easier to react with CMAS to form an apatite phase.
查看更多>>摘要：The Al alloy and carbon fiber reinforced polymer(CFRP)hybrid structures,incorporating the performance advantages of the two materials,have been attracting more attention in high-end manufacturing fields.In the current investigation,the flat friction spot joining(FSJ)was employed in joining the AA6061-T6 alloy and CFRP sheets.The significance of temperature distribution in influencing joint quality was highlighted through analyzing interface microstructural features,weld defect formation as well as fractography.To understand the role of thermal energy generation and conduction in the process comprehensively,a 3D thermal-mechanical coupling finite element model was established.The interfacial temperature was char-acterized by an uneven distribution behavior due to the inhomogeneous heat distribution.The peak tem-peratures on the top surface and Al alloy to CFRP interface at 1500 rpm rotational speed with 0.1 mm/s plunging speed were 498℃and 489℃,respectively.The peak interface temperature was reduced to 286℃at 250 rpm,which produced an extremely small melted area.Compared with the plunging speed,rotational speed was found to be the predominant parameter for determining the joint property,which could be optimized to simultaneously realize the avoidance of thermal decomposition of CFRP,the suffi-cient melting duration time,and the wide enough melted area.Simulated thermal histories and melted area profiles were in agreement with experimental ones.The findings could be utilized to provide some feasible guidance for process optimization of dissimilar FSJ of metals and composites.
查看更多>>摘要：NiCoCr-based multi-component alloys have drawn much attention due to their exceptional ductility and strain hardening capacity.However,insufficient strength-ductility synergy of NiCoCr alloy has always been an issue that prevents it from extensive applications.According to our previous research,the precipitation of γ"phase can significantly improve the strength-ductility synergy of this alloy system at room temperature.In this study,the effects of V addition on γ"phase stability and high-temperature mechanical properties have been explicitly investigated.The results indicate that V addition can sta-bilize the metastable γ"phase in this alloy system and prevent it from transforming into a stable δphase at grain boundaries upon 650℃aging,resulting in improved mechanical properties at elevated temperatures.The specific strength of γ"-strengthened multi-component NiCoCr-based alloy can reach up to 86.2 MPa g-1 cm-3 at 650℃,which is higher than those of Ni-based superalloys,IN 939 and Waspaloy.This work provides theoretical guidance for the novel design of γ"-strengthened alloy for high-temperature applications.
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