Mn segregation at austenite/ferrite interface is studied in a Fe-C-Mn-Si alloy held at 656℃. Mn is partitioned during the growth of ferrite and as a result, a Mn pile-up exists in front of interface on the matrix sid...Mn segregation at austenite/ferrite interface is studied in a Fe-C-Mn-Si alloy held at 656℃. Mn is partitioned during the growth of ferrite and as a result, a Mn pile-up exists in front of interface on the matrix side. An approach to evaluate Mn segregation quantitatively is developed by combining STEM raster window scanning and simulation of the interaction of the electron beam with the sample to subtract the contribution of Mn pile-up and obtain pure Mn segregation value. The evaluated maximum Mn interfacial segregation is in the order of a half-monolayer.展开更多
Cu-Cr alloys are widely applied in electronic,aerospace and nuclear industries,due to their high strength and high conductivity.However,their terrible softening resistance limits wider applications.This paper presents...Cu-Cr alloys are widely applied in electronic,aerospace and nuclear industries,due to their high strength and high conductivity.However,their terrible softening resistance limits wider applications.This paper presents a novel strategy of integrating mechanism features into interpretable machine learning(ML)to develop softening-resistant Cu-Cr alloys and to understand their mechanisms.First,the mechanism features were specially designed to describe mechanisms potentially vital to softening resistance,and they were obtained through first-principles calculations.Those mechanism features that described interfacial segregation and solute diffusion exhibited significant Gini importance during feature selection.Only integrated with them,did ML models achieve great performance,accurate predictions,and successful development of Cu-0.4Cr-0.10La/Ce(wt.%)alloys with excellent softening resistance.Then,the contributions of these mechanism features to the predictions were interpreted by a game theoretic approach,but unexpectedly,they were not fully consistent with interpretations that we expected from mechanism features.Finally,investigation targeted at these inconsistencies gave novel insights into softening resistance mechanisms.The Cu-Cr-La/Ce alloys’excellent softening resistance was not induced by a prevailing mechanism of La/Ce atoms segregating at phase interfaces,nor by an expected mechanism of La/Ce atoms improving the Cr atom jump energy barriers.Instead,it was caused by a unique mechanism in which La/Ce atoms competed with Cr atoms for vacancies and therefore depleted the available vacancies for the Cr atom jump.This paper demonstrates a new paradigm of developing softening-resistant Cu-Cr alloys and understanding their mechanisms via mechanism-informed interpretable ML.展开更多
Plastic prestraining was applied to a solder interconnect to introduce internal defects such as dislocations in order to investigate the interaction of dislocations with electromigration damage. Above a critical prest...Plastic prestraining was applied to a solder interconnect to introduce internal defects such as dislocations in order to investigate the interaction of dislocations with electromigration damage. Above a critical prestrain, Bi interfacial segregation to the anode, a clear indication of electromigration damage in SnBi solder inter- connect, was effectively prevented. Such an inhibiting effect is apparently contrary to the common notion that dislocations often act as fast diffusion paths. It is suggested that the dislocations introduced by plastic prestraining acted as sinks for vacancies in the early stage of the electromigration process, but as the vacancies accumulated at the dislocations, climb of those dislocations prompted recovery of the deformed samples under current stressing, greatly decreasing the density of dislocation and vacancy in the solder, leading to slower diffusion of Bi atoms.展开更多
Segregation of solutes/impurities in the interfaces plays a decisive role in material performances.However,the segregation of solutes/impurities remains elusive due to the diversity of interfacial structures.Here,in a...Segregation of solutes/impurities in the interfaces plays a decisive role in material performances.However,the segregation of solutes/impurities remains elusive due to the diversity of interfacial structures.Here,in a Mg-Nd-Mn ternary model system,two ordered novel two-dimensional(2D)interfacial superstructures formed by periodic segregation of solute atoms in special symmetric and asymmetric tilt grain boundaries(GBs)have been systematically investigated.Z-Contrast high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)observations provided the atomic-level details on how solute atoms were arranged on these special partially coherent tilt GBs.The strained conditions of each atomic site at the tilt GBs were accurately reproduced by molecular dynamics(MD)simulations plus Voronoi analysis,and the rationality of solute segregation in each atomic-site was evaluated carefully based on the first-principles calculations.These findings expand our knowledge of solute/impurity segregation behaviors in the interfaces,especially the co-segregation behaviors in multi-component materials.展开更多
In Mg-Ca alloys the grain refining mechanism,in particular regarding the role of nucleant substrates,remains the object of debates.Although native MgO is being recognised as a nucleating substrate accounting for grain...In Mg-Ca alloys the grain refining mechanism,in particular regarding the role of nucleant substrates,remains the object of debates.Although native MgO is being recognised as a nucleating substrate accounting for grain refinement of Mg alloys,the possible interactions of MgO with alloying elements that may alter the nucleation potency have not been elucidated yet.Herein,we design casting experiments of Mg-xCa alloys varied qualitatively in number density of native MgO,which are then comprehensively studied by advanced electron microscopy.The results show that grain refinement is enhanced as the particle number density of MgO increases.The native MgO particles are modified by interfacial layers due to the co-segregation of Ca and N solute atoms at the MgO/Mg interface.Using aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy,we reveal the nature of these Ca/N interfacial layers at the atomic scale.Irrespective of the crystallographic termination of MgO,Ca and N co-segregate at the MgO/Mg interface and occupy Mg and O sites,respectively,forming an interfacial structure of a few atomic layers.The interfacial structure is slightly expanded,less ordered and defective compared to the MgO matrix due to compositional deviations,whereby the MgO substrate is altered as a poorer template to nucleate Mg solid.Upon solidification in a TP-1 mould,the impotent MgO particles account for the grain refining mechanism,where they are suggested to participate into nucleation and grain initiation processes in an explosive manner.This work not only reveals the atomic engineering of a substrate through interfacial segregation but also demonstrates the effectiveness of a strategy whereby native MgO particles can be harnessed for grain refinement in Mg-Ca alloys.展开更多
The evolution of interfacial structures of needle-like sulfides in a Hf-containing Ni-based single-crystal superalloy has been studied with a combination of the state-of-the-art spherical aberration-corrected scanning...The evolution of interfacial structures of needle-like sulfides in a Hf-containing Ni-based single-crystal superalloy has been studied with a combination of the state-of-the-art spherical aberration-corrected scanning transmission electron microscope and three-dimensional electron diffraction methods.The Hf_(2)S precipitates possess an ABACBC stacking sequence with layered structure of Hf-S-Hf-Hf-S-Hf.The Hf_(2)S/γ′interfaces exhibit different types of metastable interfacial structures,including the sharp interface with segregated Hf atom columns,the one with indistinct transition region and the one with ordered transition region.These metastable structures represent the different stages of Hf_(2)S growth during the aging process,based on which a sequential layer-by-layer growth mechanism of Hf_(2)S is proposed.展开更多
With significantly enhanced irradiation resistance,high-temperature strength,and creep resistance,oxide-dispersion-strengthened tungsten(ODS-W)alloys present tremendous potential for high-temperature applications.Howe...With significantly enhanced irradiation resistance,high-temperature strength,and creep resistance,oxide-dispersion-strengthened tungsten(ODS-W)alloys present tremendous potential for high-temperature applications.However,the oxide particles tend to segregate at W grain boundary and grow up(even to micron),greatly suppressing their strengthening effect.It is always a great challenge to effectively refine and disperse the oxide particles at W grain boundary.Here,we successfully developed a new type of cation-doped W-Y2O3 alloy via a wet chemical method and subsequent low-temperature sintering.It was found that proper cation doping could not only significantly refine the intergranular Y2O3 second phase particles but also dramatically improve the sinterability of W matrix.These doping effects,as a result,simultaneously enhance the strength and ductility of the W-Y2O3 alloy.It was confirmed that the segregation of cation dopants at the W/Y2O3 interface is the origin of these doping effects.Furthermore,X-ray photoemission spectra(XPS)analyses confirmed that cation dopant segregation also obviously affects the chemical bonding(i.e.,W–O bond)along the W/Y2O3 interface.As a result,the ratelimiting mechanism for W grain growth is influenced remarkably,explaining well the difference of W grain size in various cation-doped W-Y2O3 alloys.For the refinement of intergranular Y2O3 particles,it can be understood well from both thermodynamic and kinetic views.Detailedly,W/Y2O3 interfacial energy and atom mobility for Y2O3 coarsening are all limited by cation dopant segregation.More importantly,this cation-doping approach can also be applicable to other ODS alloys for enhancing their comprehensive mechanical properties.展开更多
基金supported by the National Natural Science Foundation of China under grant No. 50601002the Scientific Research Foundation for the Returned Over-seas Chinese Scholars, State Education Ministry
文摘Mn segregation at austenite/ferrite interface is studied in a Fe-C-Mn-Si alloy held at 656℃. Mn is partitioned during the growth of ferrite and as a result, a Mn pile-up exists in front of interface on the matrix side. An approach to evaluate Mn segregation quantitatively is developed by combining STEM raster window scanning and simulation of the interaction of the electron beam with the sample to subtract the contribution of Mn pile-up and obtain pure Mn segregation value. The evaluated maximum Mn interfacial segregation is in the order of a half-monolayer.
基金supported by the National Key Research and Development Program of China(Grant No.2021YFB3803100)the National Natural Science Foundation of China(Grant No.U2202255)+3 种基金the Science and Technology Innovation Program of Hunan Province(Grant No.2021GK2016)the Major Science and Technology Pro-gram of Wuhu,China(Grant No.2021zd02)the Hunan Natural Science Fund for Distinguished Young Scholars(No.2024JJ2076)the Project of Innovation-Driven Plan and the Project of State Key Laboratory of Powder Metallurgy,Central South University,Changsha,China.
文摘Cu-Cr alloys are widely applied in electronic,aerospace and nuclear industries,due to their high strength and high conductivity.However,their terrible softening resistance limits wider applications.This paper presents a novel strategy of integrating mechanism features into interpretable machine learning(ML)to develop softening-resistant Cu-Cr alloys and to understand their mechanisms.First,the mechanism features were specially designed to describe mechanisms potentially vital to softening resistance,and they were obtained through first-principles calculations.Those mechanism features that described interfacial segregation and solute diffusion exhibited significant Gini importance during feature selection.Only integrated with them,did ML models achieve great performance,accurate predictions,and successful development of Cu-0.4Cr-0.10La/Ce(wt.%)alloys with excellent softening resistance.Then,the contributions of these mechanism features to the predictions were interpreted by a game theoretic approach,but unexpectedly,they were not fully consistent with interpretations that we expected from mechanism features.Finally,investigation targeted at these inconsistencies gave novel insights into softening resistance mechanisms.The Cu-Cr-La/Ce alloys’excellent softening resistance was not induced by a prevailing mechanism of La/Ce atoms segregating at phase interfaces,nor by an expected mechanism of La/Ce atoms improving the Cr atom jump energy barriers.Instead,it was caused by a unique mechanism in which La/Ce atoms competed with Cr atoms for vacancies and therefore depleted the available vacancies for the Cr atom jump.This paper demonstrates a new paradigm of developing softening-resistant Cu-Cr alloys and understanding their mechanisms via mechanism-informed interpretable ML.
基金supported by the National Natural Science Foundation of China (Grant No. 51171191)the National Basic Research Program of China (Grant No. 2010CB631006)the Natural Science Foundation of Liaoning Province, China (Grant No. 20092076)
文摘Plastic prestraining was applied to a solder interconnect to introduce internal defects such as dislocations in order to investigate the interaction of dislocations with electromigration damage. Above a critical prestrain, Bi interfacial segregation to the anode, a clear indication of electromigration damage in SnBi solder inter- connect, was effectively prevented. Such an inhibiting effect is apparently contrary to the common notion that dislocations often act as fast diffusion paths. It is suggested that the dislocations introduced by plastic prestraining acted as sinks for vacancies in the early stage of the electromigration process, but as the vacancies accumulated at the dislocations, climb of those dislocations prompted recovery of the deformed samples under current stressing, greatly decreasing the density of dislocation and vacancy in the solder, leading to slower diffusion of Bi atoms.
基金financially supported by the National Key Research and Development Program of China(No.2021YFB3701002)the National Natural Science Foundation of China(No.52101129)the Fundamental Research Funds for the Central Universities(Nos.N2202013 and N2007011).
文摘Segregation of solutes/impurities in the interfaces plays a decisive role in material performances.However,the segregation of solutes/impurities remains elusive due to the diversity of interfacial structures.Here,in a Mg-Nd-Mn ternary model system,two ordered novel two-dimensional(2D)interfacial superstructures formed by periodic segregation of solute atoms in special symmetric and asymmetric tilt grain boundaries(GBs)have been systematically investigated.Z-Contrast high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)observations provided the atomic-level details on how solute atoms were arranged on these special partially coherent tilt GBs.The strained conditions of each atomic site at the tilt GBs were accurately reproduced by molecular dynamics(MD)simulations plus Voronoi analysis,and the rationality of solute segregation in each atomic-site was evaluated carefully based on the first-principles calculations.These findings expand our knowledge of solute/impurity segregation behaviors in the interfaces,especially the co-segregation behaviors in multi-component materials.
基金financial support under grant number EP/N007638/1supported by EPSRC under grant number EP/W021080/1
文摘In Mg-Ca alloys the grain refining mechanism,in particular regarding the role of nucleant substrates,remains the object of debates.Although native MgO is being recognised as a nucleating substrate accounting for grain refinement of Mg alloys,the possible interactions of MgO with alloying elements that may alter the nucleation potency have not been elucidated yet.Herein,we design casting experiments of Mg-xCa alloys varied qualitatively in number density of native MgO,which are then comprehensively studied by advanced electron microscopy.The results show that grain refinement is enhanced as the particle number density of MgO increases.The native MgO particles are modified by interfacial layers due to the co-segregation of Ca and N solute atoms at the MgO/Mg interface.Using aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy,we reveal the nature of these Ca/N interfacial layers at the atomic scale.Irrespective of the crystallographic termination of MgO,Ca and N co-segregate at the MgO/Mg interface and occupy Mg and O sites,respectively,forming an interfacial structure of a few atomic layers.The interfacial structure is slightly expanded,less ordered and defective compared to the MgO matrix due to compositional deviations,whereby the MgO substrate is altered as a poorer template to nucleate Mg solid.Upon solidification in a TP-1 mould,the impotent MgO particles account for the grain refining mechanism,where they are suggested to participate into nucleation and grain initiation processes in an explosive manner.This work not only reveals the atomic engineering of a substrate through interfacial segregation but also demonstrates the effectiveness of a strategy whereby native MgO particles can be harnessed for grain refinement in Mg-Ca alloys.
基金This work is supported by the Basic Science Center Program for Multiphase Evolution in Hypergravity of the National Natural Science Foundation of China(Grant No.51988101)the National Natural Science Foundation of China(Grant Nos.52071284 and 51971203)Jiangwei Wang acknowledges the support of the Innovation Fund of the Zhejiang Kechuang New Materials Research Institute(ZKN-18-Z02).
文摘The evolution of interfacial structures of needle-like sulfides in a Hf-containing Ni-based single-crystal superalloy has been studied with a combination of the state-of-the-art spherical aberration-corrected scanning transmission electron microscope and three-dimensional electron diffraction methods.The Hf_(2)S precipitates possess an ABACBC stacking sequence with layered structure of Hf-S-Hf-Hf-S-Hf.The Hf_(2)S/γ′interfaces exhibit different types of metastable interfacial structures,including the sharp interface with segregated Hf atom columns,the one with indistinct transition region and the one with ordered transition region.These metastable structures represent the different stages of Hf_(2)S growth during the aging process,based on which a sequential layer-by-layer growth mechanism of Hf_(2)S is proposed.
基金the National Natural Science Foundation of China(51822404)the Science and Technology Program of Tianjin(19YFZCGX00790 and 18YFZCGX00070)+1 种基金the Natural Science Foundation of Tianjin(18JCYBJC17900)the Seed Foundation of Tianjin University(2018XRX-0005)。
文摘With significantly enhanced irradiation resistance,high-temperature strength,and creep resistance,oxide-dispersion-strengthened tungsten(ODS-W)alloys present tremendous potential for high-temperature applications.However,the oxide particles tend to segregate at W grain boundary and grow up(even to micron),greatly suppressing their strengthening effect.It is always a great challenge to effectively refine and disperse the oxide particles at W grain boundary.Here,we successfully developed a new type of cation-doped W-Y2O3 alloy via a wet chemical method and subsequent low-temperature sintering.It was found that proper cation doping could not only significantly refine the intergranular Y2O3 second phase particles but also dramatically improve the sinterability of W matrix.These doping effects,as a result,simultaneously enhance the strength and ductility of the W-Y2O3 alloy.It was confirmed that the segregation of cation dopants at the W/Y2O3 interface is the origin of these doping effects.Furthermore,X-ray photoemission spectra(XPS)analyses confirmed that cation dopant segregation also obviously affects the chemical bonding(i.e.,W–O bond)along the W/Y2O3 interface.As a result,the ratelimiting mechanism for W grain growth is influenced remarkably,explaining well the difference of W grain size in various cation-doped W-Y2O3 alloys.For the refinement of intergranular Y2O3 particles,it can be understood well from both thermodynamic and kinetic views.Detailedly,W/Y2O3 interfacial energy and atom mobility for Y2O3 coarsening are all limited by cation dopant segregation.More importantly,this cation-doping approach can also be applicable to other ODS alloys for enhancing their comprehensive mechanical properties.
