查看更多>>摘要：The reliability of the coated industry components demands ideal fatigue properties of the coating,and it is mainly determined by the performance of the interfaces.In this study,pulsed magnetic treatment(PMT)was applied to the thermal sprayed WC-10Co4Cr coating,and the fatigue lifetime of the coated bolt increased by 219.82％under an imitation of the operating mode condition.Scratch tests further proved that both the adhesion and cohesion strength were improved after PMT,and they benefit from the inter-face strengthening effects.The formation of coherent WC/Co interfaces was characterized by in-situ transmission electron microscopy(TEM),and the molecular dynamic simulations indicate that the work of separation of these interfaces is much higher than the original disordered ones.Residual stress was relaxed and distributed more homoge-neously after PMT,and it mainly contributes to the coat-ing/substrate strengthening.This work provides a new post-treatment method focusing on the interfaces in the WC-based coating and gives insight into its mechanism so that it is hopeful to be applied to other kinds of coatings.
查看更多>>摘要：CaCu3Ti4O12(CCTO)ceramic nanocomposites incorporating graphene-carbon black(GRCB)fillers were fabricated by spark plasma sintering process.The per-colative effects of conductive GRCB fillers on dielectric response of GRCB/CCTO ternary metacomposites were systematically investigated.The weakly real permittivity(ε')-negative response(ε'～-1 × 102)was achieved which originated from weakly low-frequency plasmonic state of free carriers within constructed GRCB networks.With enhancing three-dimensional GRCB network,the plasma frequency of metacomposites increased while the damping factor decreased.Herein,the e'-negative values of metacomposites were tuned from-102 to-104 orders of magnitude and ε'-near-zero(ENZ)frequencies from～142 to～340 MHz which substantially benefited from the moderate carrier concentration of GRCB dual fillers.The Drude model and equivalent circuit models were adopted to demonstrate dielectric and electrical character-istics.The obtained metacomposites show strong EM shielding effect along with enhanced plasmonic oscillation and even better achieving perfect EM shielding effect in ENZ media.This work achieves the tunable ε'-negative andε'-near-zero response and more importantly clarifies its regulation mechanism in ceramic-based ternary metacom-posites,which opens up the possibility of designing high-performance EM shielding materials based on metacom-posites.
查看更多>>摘要：In this paper,the interrupted and ruptured creep tests were carried out in a novel second generation single crystal superalloy named DD11 at 1100 ℃/130 MPa.The alloy exhibited typical creep curve including primary,steady,and tertiary three creep stages.The microstructural evolution at different stages of the creep were analyzed by scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The results show that the γ'phases transform into rafted structure at the early stage of the steady creep and keep stable during the steady creep stage.As the creep goes on,the rafted structure further coarsens and the topological inversion occurs.In addition,at the primary creep,the dislocations mainly move in the γmatrix and pile up in the γ/γ'interface since the matrix channels widen slightly.The formation of the regular interfacial dislocation networks occurs at the early stage of the steady creep.Under the low stress,the dominated deformation mechanism during steady creep stage is the climbing of the(010)type edge dislocation.Furthermore,the effect of the deformation mechanism on creep property was discussed in detail.
查看更多>>摘要：Tailoring the alloy composition,which induces the hard secondary phase to increase hardness and strength to improve the wear features,is a feasible approach for developing wear-resistant metal materials.Here,a group of(AlCoCrFeNi)100-xScx(x=0-2.0,at％)high-entropy alloys(HEAs)are designed and the phase compositions and wear behaviors are explored.Sc-doped HEA series contain the primary body-centered cubic(BCC)and eutectic phases,in which the eutectic phase is composed of the alternately grown BCC and Laves phases.Sc addition promotes the diffusion of Ni atoms from BCC phase to form the Sc-rich Laves phase at the grain boundaries.Vickers hardness increases due to solid solution strength-ening and second phase strengthening.And the second phase strengthening plays a more significant role relative to solid solution strengthening.Laves phase and the oxides caused by wear heating prevent the direct contact between friction pair and HEAs,thus inducing a decreased wear rate from 6.82 × 10-5 to 3.47 × 10-5 m3·N-1·m-1.Moreover,the wear mechanism changes from adhesive wear,abrasive wear and oxidative wear to abrasive wear and oxidative wear.
查看更多>>摘要：In order to accelerate the research on the property optimization of titanium alloy based on high-throughput methods,it is necessary to reveal the relation-ship between hardness and other mechanical properties which is still unclear.In this work,taking Ti20C alloy as research object,almost all the microstructure of dual-phase titanium alloys were covered by traversing over 100 heat treatment schemes.Then,massive experiments including microstructure characterization and performance test were conducted,obtaining 51,590 pieces of microstructure data and 3591 pieces of mechanical property data.Subse-quently,based on large-scale data-driven technology,the quantitative mapping relationship between hardness and other mechanical properties was deeply discussed.The results of random forest models showed that the correlation between hardness(H)and Charpy impact energy(Ak)(or elongation,A)was hardly dependent on the microstructure types,while the relationship between H and tensile strength(Rm)(or yield strength,Rp0.2)was highly dependent on microstructure types.Specifically,combined with statisti-cal analysis,it was found that the relationship between H and Ak(or A)were negatively linear.Interestingly,the relationship between H and strength was positively linear for equiaxed microstructure,and strength was linked to d-1/2(d,equivalent circle diameter)of α-grains in the form of classical Hall-Petch formula;but for other microstruc-tures,the relationships were quadratic.Furthermore,the above rules were nearly the same in the rolling direction and transverse direction.Finally,a"four-quadrant partition map"between H and Rp0.2/Rm was established as a ver-satile material-screening tool,which can provide guidance for on-demand selection of titanium alloys.
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