By using molecular dynamics computer simulation at atomic level, the effects of single dislocation and dipole dislocations on nucleation and growth of martensitic transformation have been studied. It was found that o...By using molecular dynamics computer simulation at atomic level, the effects of single dislocation and dipole dislocations on nucleation and growth of martensitic transformation have been studied. It was found that only the location of tension or compression stress fields of the dislocations are favorable for martensite nucleation in NiAl alloy and the dislocations can move to accommodate partly the transformation strain during the nucleation and growth of martensite. Combined with the molecular dynamics simulation, a two dimensional simulation for martensite morphology based on a dislocation model has been performed. Many factors related to martensitic transformation were considered, such as supercooling, interface energy, shear strain, normal strain and hydrostatic pressure. Different morphologies of martensites, similar to lath, lenticular, thin plate, couple-plate and lenticular couple-plate martensites observed in Fe-C and Fe-Ni-C alloys, were obtained.展开更多
The effect of the amount of Sn on the formation of fcc phase in Ti-13 Ta-x Sn(x=3,6,9 and 12,at.%)alloys was studied.The alloys were synthesized by mechanical alloying using a planetary mill,jar and balls of stabilize...The effect of the amount of Sn on the formation of fcc phase in Ti-13 Ta-x Sn(x=3,6,9 and 12,at.%)alloys was studied.The alloys were synthesized by mechanical alloying using a planetary mill,jar and balls of stabilized yttrium.Using Rietveld refinement,it was found that the obtained fcc phase has crystallite size smaller than 10 nm and microstrain larger than 10-3.Both conditions are required to form an fcc phase in Ti-based alloys.For all samples,the microstructure of the fcc phase consists of equiaxial crystallites with sizes smaller than 10 nm.The largest presence of fcc phase in the studied Ti alloy was found with 6 at.%Sn,because this alloy exhibits the largest microstrain(1.5×10-2)and crystallite size of 6.5 nm.Experimental data reveal that a solid solution and an amorphous phase were formed during milling.The necessary conditions to promote the formation of solid solution and amorphous phases were determined using thermodynamic calculations.When the amount of Sn increases,the energy required to form an amorphous phase varies from approximately 10 to approximately-5 k J/mol for 3 and 12 at.%Sn,respectively.The thermodynamic calculations are in agreement with XRD patterns analysis and HRTEM results.展开更多
To explore the effect of temperature on the phase transformation of HCP→FCC during compression, the uniaxial compression process of AZ31 magnesium alloy was simulated by the molecular dynamics method, and the changes...To explore the effect of temperature on the phase transformation of HCP→FCC during compression, the uniaxial compression process of AZ31 magnesium alloy was simulated by the molecular dynamics method, and the changes of crystal structure and dislocation evolution were observed. The effects of temperature on mechanical properties, crystal structure, and dislocation evolution of magnesium alloy during compression were analyzed. It is concluded that some of the Shockley partial dislocation is related to FCC stacking faults. With the help of TEM characterization, the correctness of the correlation between some of the dislocations and FCC stacking faults is verified. Through the combination of simulation and experiment, this paper provides an idea for the in-depth study of the solid-phase transformation of magnesium alloys and provides reference and guidance for the design of magnesium alloys with good plasticity and formability at room temperature.展开更多
By means of X-ray diffraction profile analysis of three different composition Fe?Mn?Si alloys, the relationship between stacking fault probabilityP sf with the concentrations of constituents in alloys, 1/P sf =540.05+...By means of X-ray diffraction profile analysis of three different composition Fe?Mn?Si alloys, the relationship between stacking fault probabilityP sf with the concentrations of constituents in alloys, 1/P sf =540.05+23.70× Mn wt%-138.74×Si wt%, was determined. According to the nucleation mechanism by stacking fault in this alloy, the equation between critical driving force ?G c andP sf ?G c=67.487+0.177 5/P sf (J/mol), was made. Therefore, the relationship between critical driving force and compositions was established. Associated with the thermodynamic calculation, theM s of fcc (γ)→ hcp(ε) martensitic transformation in any suitable composition Fe?Mn?Si shape memory alloys can be predicted and results seem reasonable as compared with some experimental data.展开更多
文摘By using molecular dynamics computer simulation at atomic level, the effects of single dislocation and dipole dislocations on nucleation and growth of martensitic transformation have been studied. It was found that only the location of tension or compression stress fields of the dislocations are favorable for martensite nucleation in NiAl alloy and the dislocations can move to accommodate partly the transformation strain during the nucleation and growth of martensite. Combined with the molecular dynamics simulation, a two dimensional simulation for martensite morphology based on a dislocation model has been performed. Many factors related to martensitic transformation were considered, such as supercooling, interface energy, shear strain, normal strain and hydrostatic pressure. Different morphologies of martensites, similar to lath, lenticular, thin plate, couple-plate and lenticular couple-plate martensites observed in Fe-C and Fe-Ni-C alloys, were obtained.
基金financial support from FONDECYT Project No.1190797FONDEQUIP/EQM Project No.140095。
文摘The effect of the amount of Sn on the formation of fcc phase in Ti-13 Ta-x Sn(x=3,6,9 and 12,at.%)alloys was studied.The alloys were synthesized by mechanical alloying using a planetary mill,jar and balls of stabilized yttrium.Using Rietveld refinement,it was found that the obtained fcc phase has crystallite size smaller than 10 nm and microstrain larger than 10-3.Both conditions are required to form an fcc phase in Ti-based alloys.For all samples,the microstructure of the fcc phase consists of equiaxial crystallites with sizes smaller than 10 nm.The largest presence of fcc phase in the studied Ti alloy was found with 6 at.%Sn,because this alloy exhibits the largest microstrain(1.5×10-2)and crystallite size of 6.5 nm.Experimental data reveal that a solid solution and an amorphous phase were formed during milling.The necessary conditions to promote the formation of solid solution and amorphous phases were determined using thermodynamic calculations.When the amount of Sn increases,the energy required to form an amorphous phase varies from approximately 10 to approximately-5 k J/mol for 3 and 12 at.%Sn,respectively.The thermodynamic calculations are in agreement with XRD patterns analysis and HRTEM results.
基金supported by the National Key Research and Development Project (2018YFB1307902)Shanxi Province Joint Student Training Base Talent Training Project(No.2018JD33)+5 种基金Shanxi young top talent projectShanxi Province Science Foundation for Youths (201901D211312)Excellent young academic leaders in Shanxi colleges and universities(No.2019045)Excellent Achievements Cultivation Project of Shanxi Higher Education Institutions(No.2019KJ028)Shanxi Province emerging industry leader talent projectShanxi Graduate Education Innovation Project(No.2019SY482)。
文摘To explore the effect of temperature on the phase transformation of HCP→FCC during compression, the uniaxial compression process of AZ31 magnesium alloy was simulated by the molecular dynamics method, and the changes of crystal structure and dislocation evolution were observed. The effects of temperature on mechanical properties, crystal structure, and dislocation evolution of magnesium alloy during compression were analyzed. It is concluded that some of the Shockley partial dislocation is related to FCC stacking faults. With the help of TEM characterization, the correctness of the correlation between some of the dislocations and FCC stacking faults is verified. Through the combination of simulation and experiment, this paper provides an idea for the in-depth study of the solid-phase transformation of magnesium alloys and provides reference and guidance for the design of magnesium alloys with good plasticity and formability at room temperature.
基金Project supported by the National Natural Science Foundation of China (Grant No. 59671023).
文摘By means of X-ray diffraction profile analysis of three different composition Fe?Mn?Si alloys, the relationship between stacking fault probabilityP sf with the concentrations of constituents in alloys, 1/P sf =540.05+23.70× Mn wt%-138.74×Si wt%, was determined. According to the nucleation mechanism by stacking fault in this alloy, the equation between critical driving force ?G c andP sf ?G c=67.487+0.177 5/P sf (J/mol), was made. Therefore, the relationship between critical driving force and compositions was established. Associated with the thermodynamic calculation, theM s of fcc (γ)→ hcp(ε) martensitic transformation in any suitable composition Fe?Mn?Si shape memory alloys can be predicted and results seem reasonable as compared with some experimental data.
