Microscopic phase-field method was used to simulate the site occupation of a series of alloys with a stoichiometric composition of Ni75Al25?xFex (x=0, 5?10) aged at 1273 K. With the change of Fe content, quantitative ...Microscopic phase-field method was used to simulate the site occupation of a series of alloys with a stoichiometric composition of Ni75Al25?xFex (x=0, 5?10) aged at 1273 K. With the change of Fe content, quantitative calculations were made on each atomic site occupation probability (SOP) in L12-Ni3 (Al1?xFex), so as to find out the dynamic response law. The result of the study shows that, with the increase of Fe content, the Fe atom preferentially occupies the B sites (corner sites of FCC) with its SOP value being increased gradually, and the SOP of the Al atom on the B sites is greatly decreased. Meanwhile, AlNi and FeNi anti-sites form in the precipitation of L12 phase. Moreover, with the increase of Fe content, the formation of AlNi and FeNi anti-sites becomes much easier. In addition, it has been found that the instantaneous dynamic evolution of the atomic SOP is completed at the early stage of the growth of L12 phases.展开更多
MnAl rare-earth-free permanent magnets exhibit excellent advantages from economic and resource perspectives,which have attracted extensive attentions in recent decades.We reported the evolution in phase formation and ...MnAl rare-earth-free permanent magnets exhibit excellent advantages from economic and resource perspectives,which have attracted extensive attentions in recent decades.We reported the evolution in phase formation and intrinsic magnetic properties ofτ-phase in binary MnAl alloys with the variation in Mn:Al ratios.Ferromagneticτ-phase can be generated within the compositional range of Mn_(50+x)Al_(50-x)(x=1–8),and pureτ-phase can only be obtained in the alloys with x=4–7.With Mn:Al ratio increasing,saturation magnetization M_(s)and magnetocrystalline anisotropy constant K_(1)are gradually weakened due to the incremental antiferromagnetic Mn-1d atoms,but Curie temperature ofτ-phase is gradually increased induced by the strengthened d-d hybridization of Mn_(1a)-Mn_(1d).An attempt of doping traces of Ti was carried out in order to eliminate the negative antiferromagnetic interaction derived from Mn-1d atom.Ti atoms tend to occupy 1d sites and replace the Mn-1d atoms due to the relatively fewer valence electrons compared with Mn,resulting in the reduction in Mn_(1a)−Mn_(1d)antiferromagnetic interactions,which is demonstrated by the higher M_(s)of Mn_(55-y)Al_(45)Ti_(y)(y=1)than that of Mn_(55)Al_(45).However,with further substitution of Mn by Ti,unfavorableκ-phase is unavoidably generated.Finally,the occupation preference and the corresponding influences on local magnetic interactions as well as the magnetizations of the different alloying atoms including interstitial element C,3d atoms Ti,Co and Cu,and main-group element Ga are systematically summarized,in order to offer the guidance of designing MnAl permanent magnets with ideal magnetic properties.展开更多
The potential energies, volumes and electronic structures of characteristic atoms coordinated by neighboring configurations were obtained from the experimental heats of formation and lattice parameters of disordered A...The potential energies, volumes and electronic structures of characteristic atoms coordinated by neighboring configurations were obtained from the experimental heats of formation and lattice parameters of disordered Au1-xCux alloys. From characteristic atom occupation （CAO） patterns of L12-Au3Cu, L12-AuCu3 and Llo-AuCu compounds, their electronic structures, volumetric and energetic properties were calculated. The CAO pattern of Johasson-Linde（J-L） model shows that the transition AuCuI→AuCulI is an exothermic and volume contraction reaction, which is opposite from experimental phenomena. According to CAO pattern of Guymont-Feutelais-Legendre（G-F-L） model, the AuCulI cell consists of two periodic antidirection （PAD） AuCuI regions and two PAD boundary regions. The equations derived from CAO pattern of G-F-L model can be used to calculate energetic properties, volumetric properties and ordering degrees of the PAD AuCuI region and PAD boundary region, as well as corresponding average properties of the AuCulI phase. The results are consistent with experimental phenomena.展开更多
Improving brittle behavior and mechanical properties is still a big challenge for high-temperature structural materials.By means of first-principles calculations,in this paper,we systematically investigate the effect ...Improving brittle behavior and mechanical properties is still a big challenge for high-temperature structural materials.By means of first-principles calculations,in this paper,we systematically investigate the effect of vacancy and oxygen occupation on the elastic properties and brittle-or-ductile behavior on Mo_(5)Si_(3).Four vacancies(Si_(-Va1),Si_(-Va2),Mo_(-Va1),Mo_(-Va2))and oxygen occupation models(O_(Mo1),O_(Mo2),O_(-Si1),O_(-Si2))are selected for research.It is found that Mo_(-Va2) vacancy has the stronger structural stability in the ground state in comparison with other vacancies.Besides,the deformation resistance and hardness of the parent Mo_(5)Si_(3) are weakened due to the introduction of different vacancy defects and oxygen occupation.The ratio of B/G indicates that oxygen atoms occupation and vacancy defects result in brittle-to-ductile transition for Mo_(5)Si_(3).These vacancies and the oxygen atoms occupation change the localized hybridization between Mo-Si and Mo-Mo atoms.The weaker O-Mo bond is a contributing factor for the excellent ductile behavior in the O_(-Si2) model for Mo_(5)Si_(3).展开更多
基金Project(2013011014-1)supported by the Natural Science Funds of Shanxi Province,ChinaProject(2009021028)supported by Science and Technique Foundation for Young Scholars of Shanxi Province,China
文摘Microscopic phase-field method was used to simulate the site occupation of a series of alloys with a stoichiometric composition of Ni75Al25?xFex (x=0, 5?10) aged at 1273 K. With the change of Fe content, quantitative calculations were made on each atomic site occupation probability (SOP) in L12-Ni3 (Al1?xFex), so as to find out the dynamic response law. The result of the study shows that, with the increase of Fe content, the Fe atom preferentially occupies the B sites (corner sites of FCC) with its SOP value being increased gradually, and the SOP of the Al atom on the B sites is greatly decreased. Meanwhile, AlNi and FeNi anti-sites form in the precipitation of L12 phase. Moreover, with the increase of Fe content, the formation of AlNi and FeNi anti-sites becomes much easier. In addition, it has been found that the instantaneous dynamic evolution of the atomic SOP is completed at the early stage of the growth of L12 phases.
基金This work was supported by the National Natural Science Foundation of China(NSFC,Grant No.52271162)the Fundamental Research Funds for the Central Universities.
文摘MnAl rare-earth-free permanent magnets exhibit excellent advantages from economic and resource perspectives,which have attracted extensive attentions in recent decades.We reported the evolution in phase formation and intrinsic magnetic properties ofτ-phase in binary MnAl alloys with the variation in Mn:Al ratios.Ferromagneticτ-phase can be generated within the compositional range of Mn_(50+x)Al_(50-x)(x=1–8),and pureτ-phase can only be obtained in the alloys with x=4–7.With Mn:Al ratio increasing,saturation magnetization M_(s)and magnetocrystalline anisotropy constant K_(1)are gradually weakened due to the incremental antiferromagnetic Mn-1d atoms,but Curie temperature ofτ-phase is gradually increased induced by the strengthened d-d hybridization of Mn_(1a)-Mn_(1d).An attempt of doping traces of Ti was carried out in order to eliminate the negative antiferromagnetic interaction derived from Mn-1d atom.Ti atoms tend to occupy 1d sites and replace the Mn-1d atoms due to the relatively fewer valence electrons compared with Mn,resulting in the reduction in Mn_(1a)−Mn_(1d)antiferromagnetic interactions,which is demonstrated by the higher M_(s)of Mn_(55-y)Al_(45)Ti_(y)(y=1)than that of Mn_(55)Al_(45).However,with further substitution of Mn by Ti,unfavorableκ-phase is unavoidably generated.Finally,the occupation preference and the corresponding influences on local magnetic interactions as well as the magnetizations of the different alloying atoms including interstitial element C,3d atoms Ti,Co and Cu,and main-group element Ga are systematically summarized,in order to offer the guidance of designing MnAl permanent magnets with ideal magnetic properties.
基金Project (50711181) supported by the National Natural Science Foundation of China Project (2009FJ4016) supported by Natural Science Foundation of Hunan Province,China
文摘The potential energies, volumes and electronic structures of characteristic atoms coordinated by neighboring configurations were obtained from the experimental heats of formation and lattice parameters of disordered Au1-xCux alloys. From characteristic atom occupation （CAO） patterns of L12-Au3Cu, L12-AuCu3 and Llo-AuCu compounds, their electronic structures, volumetric and energetic properties were calculated. The CAO pattern of Johasson-Linde（J-L） model shows that the transition AuCuI→AuCulI is an exothermic and volume contraction reaction, which is opposite from experimental phenomena. According to CAO pattern of Guymont-Feutelais-Legendre（G-F-L） model, the AuCulI cell consists of two periodic antidirection （PAD） AuCuI regions and two PAD boundary regions. The equations derived from CAO pattern of G-F-L model can be used to calculate energetic properties, volumetric properties and ordering degrees of the PAD AuCuI region and PAD boundary region, as well as corresponding average properties of the AuCulI phase. The results are consistent with experimental phenomena.
基金supported by grants from the Province Nature Science Foundation of Liaoning Province(Grant No.2019JH/30100019)。
文摘Improving brittle behavior and mechanical properties is still a big challenge for high-temperature structural materials.By means of first-principles calculations,in this paper,we systematically investigate the effect of vacancy and oxygen occupation on the elastic properties and brittle-or-ductile behavior on Mo_(5)Si_(3).Four vacancies(Si_(-Va1),Si_(-Va2),Mo_(-Va1),Mo_(-Va2))and oxygen occupation models(O_(Mo1),O_(Mo2),O_(-Si1),O_(-Si2))are selected for research.It is found that Mo_(-Va2) vacancy has the stronger structural stability in the ground state in comparison with other vacancies.Besides,the deformation resistance and hardness of the parent Mo_(5)Si_(3) are weakened due to the introduction of different vacancy defects and oxygen occupation.The ratio of B/G indicates that oxygen atoms occupation and vacancy defects result in brittle-to-ductile transition for Mo_(5)Si_(3).These vacancies and the oxygen atoms occupation change the localized hybridization between Mo-Si and Mo-Mo atoms.The weaker O-Mo bond is a contributing factor for the excellent ductile behavior in the O_(-Si2) model for Mo_(5)Si_(3).
