查看更多>>摘要：An effort to obtain superior impact properties for Al-7Si-0.35 Mg alloy is presented,where modification with 0.02 wt％Sr and 0.1 wt％La as well as solution treatment was jointly employed.The samples were solution treated at 535 ℃ for 15 min to 12 h.The microstructure,fracture mecha-nism,and their correlation with the impact properties of the alloy were studied in detail mainly through optical micro-scopy(OM),scanning electron microscopy(SEM)and oscillography impact test.The results show that the addition of Sr and La refined the eutectic Si particles significantly from～2.05 pm(modified with Sr alone)to～0.75 pm in as-cast microstructure,leading to a very homogeneous dis-tribution of spheroidized Si particles in the alloy solution treated at 535 ℃ for 8 h.The alloy exhibits excellent impact toughness up to 75 J·cm-2,which is much higher than the maximum impact toughness of the alloys modified by Sr alone(～46 J·cm-2).The major reason for this remarkable increase in the impact property is the dramatic increase in crack initiation energy.The dispersoid-free zones(DFZs)near the eutectic regions mainly consist of the ductile Al-matrix,which exhibits excellent ductility.The ductile Al-matrix of the DFZs hinders the crack propagation,resulting in a significant increase in crack propagation energy.
查看更多>>摘要：This study focuses on compositionally complex alloys(CCAs),aiming to achieve a balance between high strength and low density for new energy and aerospace applications.The composition of AlCrFeNiTix CCAs is strategically guided by employing density functional the-ory and the theoretical design of thermodynamic calcula-tions.Bulk CCAs,particularly AlCrFeNiTi0.25 alloy,demonstrate remarkable specific yield strength(1640.8 MPa)and 22.7％maximum strain.The incorpo-ration of Ti facilitates the formation of lightweight and high-strength L21 phase,contributing to the overall high specific strength.Synergistic effects of grain boundary strengthening,solid solution strengthening,Orowan strengthening and Peierls flow stress further enhance strength.Detailed exploration of microstructural changes during fracture reveals the role of ordered phases in sup-pressing crack propagation and absorbing energy within disordered phases,thereby improving the toughness and fracture resistance of CCAs.These methods and discov-eries establish a robust foundation for advancing the development of novel lightweight CCAs.
查看更多>>摘要：Thermal barrier coatings(TBCs)applied in aero-engines tend to be attacked by molten calcia-magnesia-alumino-silicate(CMAS)at high operating temperatures.Yttria-stabilized zirconia(YSZ)coatings with quasi-columnar microstructure were fabricated by plasma spray physical vapor deposition(PS-PVD)technique.The chemical changes,microstructural transformation,mechanical properties and degradation mechanisms of the CMAS-interacted TBCs in the thermal cycling tests were investigated.Feathered YSZ grains were dissolved in the CMAS melts,and then the ZrO2 grains were reprecipitated with spherical shape,accompanying with phase transfor-mation from tetragonal(t)to monoclinic(m).The thermal cycling tests reveal that the YSZ coating fails at the early stage due to the attack of CMAS.The fractures in intra-columns lead to partial spallation of the coatings.The failure of the coating occurs at the interfaces between thermally grown oxides(TGO)layer and YSZ topcoat;especially,the hardness and Young's modulus of the YSZ coatings increase intensively,as the coatings were infil-trated by the CMAS for a long time.
查看更多>>摘要：Owing to the fine nano-laminated structure,the pearlitic multi-principal element alloy(PMPEA)exhibits excellent mechanical and tribological properties.However,the incomplete understanding of the size effect of its lamella thickness and the unclear understanding of the plasticity-interface interaction mechanism limit further optimization of PMPEAs.In this study,the FeCoNi/Ni3Ti interface-mediated plastic deformation behavior in PMPEA and the variation of mechanical and tribological properties with lamella thickness within the nanoscale range using molecular dynamics(MD)simulation were explored.The results indicate that the mechanical and tribological prop-erties of the PMPEA with lamella thicknesses below 10 nm have a significant inverse size effect,i.e.,the smaller the lamella thickness,the weaker the properties.This is because the plastic carrier-interface interaction mechanism changes from a strengthening mechanism that hinders dislocations to a weakening mechanism that promotes dislocations with the decreases in the lamella thickness,and the weakening effect becomes more pronounced as the lamella thickness decreases and the number of interfaces increases.In particular,the deformation behavior of Ni3Ti lamellae changes from crystal-like to amorphous-like with decreasing lamella.Moreover,in the sample with larger lamella thickness,the occurrence of hierarchical slips in the body-centered cubic(BCC)phase due to the multi-principal elements effect can better alleviate the stress concentration caused by the dislocation accumulation at the interface,so that the phase interface exhibits outstanding load-bearing effects.And the dislocation pattern in BCC phase shows a firm high-density cell,which makes the substrate exhibit a stable tribological response.
查看更多>>摘要：For the first time,the mechanism of metal alu-minum dissolution in NaF-ScF3 eutectic melts and the chemical interaction between the constituents of this mixture have been thoroughly studied by a combination of differential thermal analysis(DTA),high temperature and solid-state nuclear magnetic resonance(NMR),and X-ray diffraction(XRD)coupled with the molecular dynamic simulations.The formation of an insoluble Al3Sc alloy in molten(NaF-ScF3)eut system was proven,and the chemical mechanism of this alu-minothermic Al3Sc alloy production was elucidated.Corre-sponding ex situ examinations bring to light the formation of NaScF4 and solid solution of Na3(Al,Sc)F6 in cooled bath.The molecular dynamics calculations of the bath allow us to construct the structural model and to predict viscosity,density and electrical conductivity of the reagent melt to help to optimize the conditions of the alloy synthesis.
查看更多>>摘要：Nanocrystalline materials exhibit unique properties due to their extremely high grain boundary(GB)density.However,this high-density characteristic induces grain coars-ening at elevated temperatures,thereby limiting the widespread application of nanocrystalline materials.Recent experimental observations revealed that GB segregation and second-phase pinning effectively hinder GB migration,thereby improving the stability of nanocrystalline materials.In this study,a mod-ified phase-field model that integrates mismatch strain,solute segregation and precipitation was developed to evaluate the influence of lattice misfit on the thermal stability of nanocrys-talline alloys.The simulation results indicated that introducing a suitable mismatch strain can effectively enhance the microstructural stability of nanocrystalline alloys.By syner-gizing precipitation with an appropriate lattice misfit,the for-mation of second-phase particles in the bulk grains can be suppressed,thereby facilitating solute segregation/precipitation at the GBs.This concentrated solute segregation and precipi-tation at the GBs effectively hinders grain migration,thereby preventing grain coarsening.These findings provide a new perspective on the design and regulation of nanocrystalline alloys with enhanced thermal stability.
NETL
NSTL
万方数据