Despite the promising prospects of body-centered cubic iron(BCC Fe)in aerospace,energy transportation,and nuclear applications,the effects of extreme environments on its mechanical behaviors and deformation mechanisms...Despite the promising prospects of body-centered cubic iron(BCC Fe)in aerospace,energy transportation,and nuclear applications,the effects of extreme environments on its mechanical behaviors and deformation mechanisms remain elusive to date.In this work,the mechanical responses and deformation behaviors of BCC Fe single crystals under extreme loading conditions are investigated by performing the three-dimensional discrete dislocation dynamics simulations.It turns out that the yield strength(oy)of BCC Fe can be enhanced by increasing the strain rate()and/or decreasing the deformation temperature(T).With the strain rate increasing from=10^(2)s^(-1)to 106 s^(-1),the yield strength at 300 K rises fromσy=51.14 MPa to 1114.57 MPa.When the strain rate exceeds 10^(3)s^(-1),an elastic overshoot phenomenon appears because the applied stress and the low initial dislocation density at the early tensile stage cannot drive the plastic deformation immediately.With the temperature increasing from T=100 K to 800 K,the yield strength atσ_(y)=10^(3)3 s^(-1)decreases fromσε=64.97 MPa to 59.50 MPa.Such temperature and strain rate sensitivity of deformation behaviors are clarified from variations in the configurations of dislocation evolution and dislocation density fluxes.It is demonstrated that at low strain rate(ε≤10^(3)s^(-1))conditions,the deformation behaviors of BCC Fe are dominated by the dislocation multi-slip mechanism.With increasing strain rate to e.g.,>10^(3)s^(-1),the deformation behaviors are governed by the dislocation single-slip.Our investigation on the temperature and strain rate sensitivity of deformation behaviors provides insightful guidance for optimizing the mechanical performances of BCC Fe based ferritic steels.展开更多
A molecular dynamics model has been developed to investigate the evolution of the internal crack of nano scale during heating or compressive loading in BCC Fe. The initial configuration does not contain any pre-existi...A molecular dynamics model has been developed to investigate the evolution of the internal crack of nano scale during heating or compressive loading in BCC Fe. The initial configuration does not contain any pre-existing dislocations. In the case of heating, temperature shows a significant effect on crack evolution and the critical temperature at which the crack healing becomes possible is 673 K. In the case of compressive loading, the crack can be healed at 40 K at a loading rate 0.025 × 1018 Pa·m1/2/s in 6 × 10-12 s. The diffusion of Fe atoms into the crack area results in the healing process. However, dislocations and voids appear during healing and their positions change continuously.展开更多
采用基于密度泛函理论(DFT)的第一性原理,研究了Ni对bcc-Fe/ε-Cu界面结合的影响。建立了ε-Cu在bcc-Fe的析出模型,选取界面两侧不同阵点位置,计算Ni在不同位置的偏聚能,分析了Ni在界面区域的占位倾向,在此基础上探究了Ni对bcc-Fe/ε-C...采用基于密度泛函理论(DFT)的第一性原理,研究了Ni对bcc-Fe/ε-Cu界面结合的影响。建立了ε-Cu在bcc-Fe的析出模型,选取界面两侧不同阵点位置,计算Ni在不同位置的偏聚能,分析了Ni在界面区域的占位倾向,在此基础上探究了Ni对bcc-Fe/ε-Cu界面结合的影响。利用Rice-Wang热力学模型的计算表明,当Ni原子处于偏聚能最低的位置时,能够强化界面的结合。而界面分离功计算结果显示,Ni偏聚于bcc-Fe/ε-Cu界面后,界面分离功由279.8 m J·m^(-2)增加到286.7 m J·m^(-2),表明Ni偏聚后会使界面体系更加稳定。Ni偏聚于界面后对界面区域的电子结构也产生一定影响,差分电荷密度显示,与纯bcc-Fe/ε-Cu界面相比,Ni偏聚后会在其周围聚集较多的电子,且Ni与相邻原子之间电子云方向性更为明显;同时,Ni也使近邻Cu和Fe原子的态密度(DOS)向成键态偏移,这使得Ni偏聚加强了bcc-Fe/ε-Cu界面的结合,使界面区更为稳定。展开更多
The structure and energy of He impurities and vacancy on （001） surface of bcc iron are investigated by an ab initio method. Three cases for stabilities of a He atom at the surface are found： some of He atoms at sur...The structure and energy of He impurities and vacancy on （001） surface of bcc iron are investigated by an ab initio method. Three cases for stabilities of a He atom at the surface are found： some of He atoms at surface atomic layers （SAL） relax into vacuum gap; some of surface He atoms at octahedral interstitial site relax into more stable tetrahedral interstitial site; some of surface He atoms still stay at tetrahedral interstitial site. The un-stability of the He atom at the surface system can be explained by deformation mechanism of charge densities and electronic densities of states. It is found that formation energy of the point defects from the topmost SAL to bulk-like atomic layer increase gradually, for example, the formation energies of a monovacancy at the first five topmost SALs are equal to 0.33, 1.56, 2.04, 2.02 and 2.11 eV, respectively. The magnetic moments of Fe atoms in the surface atomic layers are also calculated.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.52171013 and 52130110)the Key Research and Development Program of Shaanxi(Grant No.2025CY-YBXM-127)+1 种基金the Natural Science Foundation of Chongqing(Grant No.CSTB2022NSCQ-MSX0369)the Research Fund of the State Key Laboratory of Solidification Processing(NPU)China(Grant No.2023-QZ-03)。
文摘Despite the promising prospects of body-centered cubic iron(BCC Fe)in aerospace,energy transportation,and nuclear applications,the effects of extreme environments on its mechanical behaviors and deformation mechanisms remain elusive to date.In this work,the mechanical responses and deformation behaviors of BCC Fe single crystals under extreme loading conditions are investigated by performing the three-dimensional discrete dislocation dynamics simulations.It turns out that the yield strength(oy)of BCC Fe can be enhanced by increasing the strain rate()and/or decreasing the deformation temperature(T).With the strain rate increasing from=10^(2)s^(-1)to 106 s^(-1),the yield strength at 300 K rises fromσy=51.14 MPa to 1114.57 MPa.When the strain rate exceeds 10^(3)s^(-1),an elastic overshoot phenomenon appears because the applied stress and the low initial dislocation density at the early tensile stage cannot drive the plastic deformation immediately.With the temperature increasing from T=100 K to 800 K,the yield strength atσ_(y)=10^(3)3 s^(-1)decreases fromσε=64.97 MPa to 59.50 MPa.Such temperature and strain rate sensitivity of deformation behaviors are clarified from variations in the configurations of dislocation evolution and dislocation density fluxes.It is demonstrated that at low strain rate(ε≤10^(3)s^(-1))conditions,the deformation behaviors of BCC Fe are dominated by the dislocation multi-slip mechanism.With increasing strain rate to e.g.,>10^(3)s^(-1),the deformation behaviors are governed by the dislocation single-slip.Our investigation on the temperature and strain rate sensitivity of deformation behaviors provides insightful guidance for optimizing the mechanical performances of BCC Fe based ferritic steels.
文摘A molecular dynamics model has been developed to investigate the evolution of the internal crack of nano scale during heating or compressive loading in BCC Fe. The initial configuration does not contain any pre-existing dislocations. In the case of heating, temperature shows a significant effect on crack evolution and the critical temperature at which the crack healing becomes possible is 673 K. In the case of compressive loading, the crack can be healed at 40 K at a loading rate 0.025 × 1018 Pa·m1/2/s in 6 × 10-12 s. The diffusion of Fe atoms into the crack area results in the healing process. However, dislocations and voids appear during healing and their positions change continuously.
文摘采用基于密度泛函理论(DFT)的第一性原理,研究了Ni对bcc-Fe/ε-Cu界面结合的影响。建立了ε-Cu在bcc-Fe的析出模型,选取界面两侧不同阵点位置,计算Ni在不同位置的偏聚能,分析了Ni在界面区域的占位倾向,在此基础上探究了Ni对bcc-Fe/ε-Cu界面结合的影响。利用Rice-Wang热力学模型的计算表明,当Ni原子处于偏聚能最低的位置时,能够强化界面的结合。而界面分离功计算结果显示,Ni偏聚于bcc-Fe/ε-Cu界面后,界面分离功由279.8 m J·m^(-2)增加到286.7 m J·m^(-2),表明Ni偏聚后会使界面体系更加稳定。Ni偏聚于界面后对界面区域的电子结构也产生一定影响,差分电荷密度显示,与纯bcc-Fe/ε-Cu界面相比,Ni偏聚后会在其周围聚集较多的电子,且Ni与相邻原子之间电子云方向性更为明显;同时,Ni也使近邻Cu和Fe原子的态密度(DOS)向成键态偏移,这使得Ni偏聚加强了bcc-Fe/ε-Cu界面的结合,使界面区更为稳定。
基金supported by National Basic Research Program of China (No.2007CB209803)the National Natural Science Foundation of China (No.51231002)the Applied Basic Research Program from Hebei Province
文摘The structure and energy of He impurities and vacancy on （001） surface of bcc iron are investigated by an ab initio method. Three cases for stabilities of a He atom at the surface are found： some of He atoms at surface atomic layers （SAL） relax into vacuum gap; some of surface He atoms at octahedral interstitial site relax into more stable tetrahedral interstitial site; some of surface He atoms still stay at tetrahedral interstitial site. The un-stability of the He atom at the surface system can be explained by deformation mechanism of charge densities and electronic densities of states. It is found that formation energy of the point defects from the topmost SAL to bulk-like atomic layer increase gradually, for example, the formation energies of a monovacancy at the first five topmost SALs are equal to 0.33, 1.56, 2.04, 2.02 and 2.11 eV, respectively. The magnetic moments of Fe atoms in the surface atomic layers are also calculated.
