Cu bicrystals of different sizes with a sole twin boundary（TB） inclined at 45？with respect to the loading direction were deformed under unidirectional and cyclic loading, respectively. It is found that the slip ba...Cu bicrystals of different sizes with a sole twin boundary（TB） inclined at 45？with respect to the loading direction were deformed under unidirectional and cyclic loading, respectively. It is found that the slip bands（SBs） parallel to the TB can be activated near the TB at all scales without obeying the Schmid＇s law.It is concerned with the local stress enhancement in the macroscale while it is more closely related to the scarce dislocation sources in the microscale. Moreover, a wedge-shaped zone formed near the TB in the microscale ascribed to the limited specimen size.展开更多
The variation of stacking fault energy(SFE)in a number of binary Cu alloys is predicted through considering the Suzuki segregation by the full potential linearly augmented plane wave(FPLAPW)method.The calculated resul...The variation of stacking fault energy(SFE)in a number of binary Cu alloys is predicted through considering the Suzuki segregation by the full potential linearly augmented plane wave(FPLAPW)method.The calculated results show that some solute atoms(Mg,Al,Si,Zn,Ga,Ge,Cd,Sn,and Pb),which prefer to form the Suzuki segregation,may decrease the value of SFE;while the others(Ti,Mn,Fe,Ni,Zr,Ag,and Au),which do not cause the Suzuki segregation may not decrease the SFE.Furthermore,it is interesting to find that the former alloying elements are located on the right of Cu group while the latter on the left of Cu group in the periodic table of elements.The intrinsic reasons for the new findings can be traced down to the valences electronic structure of solute and Cu atoms,i.e.,the similarity of valence electronic structure between solute and Cu atoms increases the value of SFE,while the difference decreases the value of SFE.展开更多
The development of multi-principal element alloys(MPEAs,also called as high-or medium-entropy al-loys,HEAs/MEAs)provides tremendous possibilities for materials innovation.However,designing MPEAs with desirable mechani...The development of multi-principal element alloys(MPEAs,also called as high-or medium-entropy al-loys,HEAs/MEAs)provides tremendous possibilities for materials innovation.However,designing MPEAs with desirable mechanical properties confronts great challenges due to their vast composition space.In this work,we provide an essential criterion to efficiently screen the CoCrNi MEAs with outstanding strength-ductility combinations.The negative Gibbs free energy difference△E_(FCC-BCC)between the face-centered cubic(FCC)and body-centered cubic(BCC)phases,the enhancement of shear modulus G and the decline of stacking fault energy(SFE)γ_(isf)are combined as three requisites to improve the FCC phase stability,yield strength,deformation mechanisms,work-hardening ability and ductility in the criterion.The effects of chemical composition on△E_(FCC-BCC),G andγisf were investigated with the first principles calculations for Co_(x)Cr_(33)Ni_(67-x),Co_(33)Cr_(y)Ni_(67-y)and Co_(z)Cr_(66-z)Ni_(34)(0≤x,y≤67 and 0≤z≤66)alloys.Based on the essential criterion and the calculation results,the composition space that displays the neg-ative Gibbs free energy difference△E_(FCC-BCC),highest shear modulus G and lowest SFEγ_(isf)was screened with the target on the combination of high strength and excellent ductility.In this context,the optimal composition space of Co-Cr-Ni alloys was predicted as 60 at.%-67 at.%Co,30 at.%-35 at.%Cr and 0 at.%-6 at.%Ni,which coincides well with the previous experimental evidence for Co_(55)Cr_(40)Ni_(5)alloys.The valid-ity of essential criterion is further proved after systematic comparison with numerous experimental data,which demonstrates that the essential criterion can provide significant guidance for the quick exploitation of strong and ductile MEAs and promote the development and application of MPEAs.展开更多
A<110>/2 screw dislocation is commonly dissociated into two <112>/6 Shockley partial dislocations on{111} planes in face-centered cubic metals.As the two partials are not purely screw,different mechanisms ...A<110>/2 screw dislocation is commonly dissociated into two <112>/6 Shockley partial dislocations on{111} planes in face-centered cubic metals.As the two partials are not purely screw,different mechanisms of cross-slip could take place,depending on the stacking fault energy,applied stress and tempe rature.It is crucial to classify the mechanisms of cross-slip because each mechanism possesses its own reaction path with a special activation process.In this work,molecular dynamics simulations have been performed systematically to explore the cross-slip mechanism under different stresses and temperatures in three different metals Ag,Cu and Ni that have different stacking fault energies of 17.8,44.4 and 126.8 mJ/m^2,re spectively.In Ag and Cu with low stacking fault energy,it is observed that the cross-slip mechanism of screw dislocations changes from the Fleischer obtuse angle(FLOA),to the Friedel-Escaig(FE),and then to the FL acute angle(FLAA) at low temperatures,with increasing the applied stress.However,when the temperature increases,the FE mechanism gradually becomes dominant,while the FLAA only occurs at the high stress region.In particular,the FLOA has not been observed in Ni because of its high stacking fault energy.展开更多
基金supported by the National Natural Science Foundation of China (NSFC) under grant Nos. 51171194, 51501197, 51571198, 51471170the IMR SYNL-T.S. Kê Research Fellowship
文摘Cu bicrystals of different sizes with a sole twin boundary（TB） inclined at 45？with respect to the loading direction were deformed under unidirectional and cyclic loading, respectively. It is found that the slip bands（SBs） parallel to the TB can be activated near the TB at all scales without obeying the Schmid＇s law.It is concerned with the local stress enhancement in the macroscale while it is more closely related to the scarce dislocation sources in the microscale. Moreover, a wedge-shaped zone formed near the TB in the microscale ascribed to the limited specimen size.
基金financially supported by the National Natural Science Foundation of China(Nos.51871223,51571198 and 51790482)the LiaoNing Revitalization Talents Program(No.XLYC1808027)。
文摘The variation of stacking fault energy(SFE)in a number of binary Cu alloys is predicted through considering the Suzuki segregation by the full potential linearly augmented plane wave(FPLAPW)method.The calculated results show that some solute atoms(Mg,Al,Si,Zn,Ga,Ge,Cd,Sn,and Pb),which prefer to form the Suzuki segregation,may decrease the value of SFE;while the others(Ti,Mn,Fe,Ni,Zr,Ag,and Au),which do not cause the Suzuki segregation may not decrease the SFE.Furthermore,it is interesting to find that the former alloying elements are located on the right of Cu group while the latter on the left of Cu group in the periodic table of elements.The intrinsic reasons for the new findings can be traced down to the valences electronic structure of solute and Cu atoms,i.e.,the similarity of valence electronic structure between solute and Cu atoms increases the value of SFE,while the difference decreases the value of SFE.
基金We sincerely acknowledge the support of the work by the Na-tional Natural Science Foundation of China(NSFC)(Nos.52130002,52071316,51871223,51771206 and 51571198)the Youth Innova-tion Promotion Association CAS(No.2021192)the KC Wong Education Foundation(No.GJTD-2020-09).
文摘The development of multi-principal element alloys(MPEAs,also called as high-or medium-entropy al-loys,HEAs/MEAs)provides tremendous possibilities for materials innovation.However,designing MPEAs with desirable mechanical properties confronts great challenges due to their vast composition space.In this work,we provide an essential criterion to efficiently screen the CoCrNi MEAs with outstanding strength-ductility combinations.The negative Gibbs free energy difference△E_(FCC-BCC)between the face-centered cubic(FCC)and body-centered cubic(BCC)phases,the enhancement of shear modulus G and the decline of stacking fault energy(SFE)γ_(isf)are combined as three requisites to improve the FCC phase stability,yield strength,deformation mechanisms,work-hardening ability and ductility in the criterion.The effects of chemical composition on△E_(FCC-BCC),G andγisf were investigated with the first principles calculations for Co_(x)Cr_(33)Ni_(67-x),Co_(33)Cr_(y)Ni_(67-y)and Co_(z)Cr_(66-z)Ni_(34)(0≤x,y≤67 and 0≤z≤66)alloys.Based on the essential criterion and the calculation results,the composition space that displays the neg-ative Gibbs free energy difference△E_(FCC-BCC),highest shear modulus G and lowest SFEγ_(isf)was screened with the target on the combination of high strength and excellent ductility.In this context,the optimal composition space of Co-Cr-Ni alloys was predicted as 60 at.%-67 at.%Co,30 at.%-35 at.%Cr and 0 at.%-6 at.%Ni,which coincides well with the previous experimental evidence for Co_(55)Cr_(40)Ni_(5)alloys.The valid-ity of essential criterion is further proved after systematic comparison with numerous experimental data,which demonstrates that the essential criterion can provide significant guidance for the quick exploitation of strong and ductile MEAs and promote the development and application of MPEAs.
基金financially supported by the Program of “One Hundred Talented People” of the Chinese Academy of Sciences (JBY)the National Natural Science Foundation of China (Nos. 51871223, 51771206, and 51790482)。
文摘A<110>/2 screw dislocation is commonly dissociated into two <112>/6 Shockley partial dislocations on{111} planes in face-centered cubic metals.As the two partials are not purely screw,different mechanisms of cross-slip could take place,depending on the stacking fault energy,applied stress and tempe rature.It is crucial to classify the mechanisms of cross-slip because each mechanism possesses its own reaction path with a special activation process.In this work,molecular dynamics simulations have been performed systematically to explore the cross-slip mechanism under different stresses and temperatures in three different metals Ag,Cu and Ni that have different stacking fault energies of 17.8,44.4 and 126.8 mJ/m^2,re spectively.In Ag and Cu with low stacking fault energy,it is observed that the cross-slip mechanism of screw dislocations changes from the Fleischer obtuse angle(FLOA),to the Friedel-Escaig(FE),and then to the FL acute angle(FLAA) at low temperatures,with increasing the applied stress.However,when the temperature increases,the FE mechanism gradually becomes dominant,while the FLAA only occurs at the high stress region.In particular,the FLOA has not been observed in Ni because of its high stacking fault energy.
