Molecular dynamics(MD) simulations were carried out to study the fracture behaviors of several symmetric tilt grain boundaries in γ-Ti Al bicrystals with <110> misorientation axes. Tensile deformation along dir...Molecular dynamics(MD) simulations were carried out to study the fracture behaviors of several symmetric tilt grain boundaries in γ-Ti Al bicrystals with <110> misorientation axes. Tensile deformation along direction perpendicular to grain boundary was simulated under various strain rates and temperatures. The results indicate that the relative orientation of the grains and the presence of certain atom units are two critical factors of the interface structure affecting the stress required for dislocation nucleation. Dislocations nucleate and extend at or near the symmetric tilt grain boundaries during the tensile deformation of Σ3(111) 109.5°, Σ9(221) 141.1° and Σ27(552) 148.4° interfaces. For Σ27(115) 31.6° and Σ11(113) 50.5° interfaces, the interfaces fractured directly in a cleavage manner due to no dislocation emitted from the boundary. The tensile fracture mechanisms of the bicrystals are that micro-cracks nucleate at the grain boundary and propagate along the interface. The variance of crack propagation is whether there is accommodation of plastic region at the crack tips.展开更多
Three types of symmetric （1120） tilt low-angle grain boundaries （LAGBs） with array of basal, prismatic, and pyramidal edge full 〈a〉 dislocations in pure Mg have been studied by using the improved Peierls-Nabarro...Three types of symmetric （1120） tilt low-angle grain boundaries （LAGBs） with array of basal, prismatic, and pyramidal edge full 〈a〉 dislocations in pure Mg have been studied by using the improved Peierls-Nabarro model in combination with the generalized stacking fault energy curve. The results show that with decreasing distance between the dislocations in all the three types of tilt LAGBs, the stress and strain fields are gradually suppressed. The reduction extent of the stress and strain fields decreases from the prismatic to basal to pyramidal dislocations. The variation of dislocation line energy （DLE） for all tilt LAGBs is divided into three stages： DLE changes slightly and linearly when the distance is larger than 300 A, - 10%; DLE declines exponentially and quickly when the distance goes from 300 to 100 A, ,- 70%; and finally, the descent speed lowers when the distance is smaller than 100 A and the dislocation core energy is nearly half of the DLE. The grain boundary energy （GBE） decreases when the tilt angle of LAGB increases from1 ° to 2° for all cases. The tilt LAGB consists of pyramidal dislocations always has the largest GBE, while that with array of prismatic dislo- cations has the smallest one in the whole range. The Peierls stress of dislocation in tilt LAGB is nearly unchanged, the same as that of single dislocation. This work is useful for further study of dissociated dislocation, solute segregation, precipitate nucleation in tilt LAGB and its interaction with single dislocations.展开更多
The movement or dissociation of dislocations is signifi cantly important for better understanding the plastic deformation mechanisms and mechanical properties of metals.It is commonly believed that a dislocation<11...The movement or dissociation of dislocations is signifi cantly important for better understanding the plastic deformation mechanisms and mechanical properties of metals.It is commonly believed that a dislocation<110>/2 in Au is easy to dissociate into a pair of Shockley partial dislocations<112>/6 due to low stacking fault energy(SFE).Contrary to this prevailing perception,the present atomistic modeling demonstrates that this reaction could be completely suppressed when dislocations<110>/2 are grouped into tilt walls,consistent with our experimental observations.Such phenomenon is actually the extreme case accompanying with the variation of Burgers vectors of partials with tilt angle,as revealed by a series of simulations,from which it is clearly seen that the Burgers vectors of partials deviate considerably from that of Shockley partials,enormously depending on the tilt angle.Our fi ndings could facilitate a better understanding on many phenomena and properties of face-centered cubic metals(FCC).展开更多
基金Project(51201147)supported by the National Natural Science Foundation of ChinaProject(14JJ6016)supported by the Natural Science Foundation of Hunan Province,ChinaProject(INFO-115-B01)supported by the Informalization Construction Project of Chinese Academy of Sciences,China
文摘Molecular dynamics(MD) simulations were carried out to study the fracture behaviors of several symmetric tilt grain boundaries in γ-Ti Al bicrystals with <110> misorientation axes. Tensile deformation along direction perpendicular to grain boundary was simulated under various strain rates and temperatures. The results indicate that the relative orientation of the grains and the presence of certain atom units are two critical factors of the interface structure affecting the stress required for dislocation nucleation. Dislocations nucleate and extend at or near the symmetric tilt grain boundaries during the tensile deformation of Σ3(111) 109.5°, Σ9(221) 141.1° and Σ27(552) 148.4° interfaces. For Σ27(115) 31.6° and Σ11(113) 50.5° interfaces, the interfaces fractured directly in a cleavage manner due to no dislocation emitted from the boundary. The tensile fracture mechanisms of the bicrystals are that micro-cracks nucleate at the grain boundary and propagate along the interface. The variance of crack propagation is whether there is accommodation of plastic region at the crack tips.
基金supported by the National Natural Science Foundation of China (Nos. 11427806, 51471067, 51371081, 51171063, 51501059 and 51501060)the National Basic Research (973) Program of China (No. 2009CB623704)+2 种基金the Chinese Postdoctoral Science Foundation (No. 2015M582324)the Hunan Provincial Natural Science Foundation (No. 14JJ4052)the Science and Technology Project for Good Postdoctoral Education of China (No. 2015RS4020)
文摘Three types of symmetric （1120） tilt low-angle grain boundaries （LAGBs） with array of basal, prismatic, and pyramidal edge full 〈a〉 dislocations in pure Mg have been studied by using the improved Peierls-Nabarro model in combination with the generalized stacking fault energy curve. The results show that with decreasing distance between the dislocations in all the three types of tilt LAGBs, the stress and strain fields are gradually suppressed. The reduction extent of the stress and strain fields decreases from the prismatic to basal to pyramidal dislocations. The variation of dislocation line energy （DLE） for all tilt LAGBs is divided into three stages： DLE changes slightly and linearly when the distance is larger than 300 A, - 10%; DLE declines exponentially and quickly when the distance goes from 300 to 100 A, ,- 70%; and finally, the descent speed lowers when the distance is smaller than 100 A and the dislocation core energy is nearly half of the DLE. The grain boundary energy （GBE） decreases when the tilt angle of LAGB increases from1 ° to 2° for all cases. The tilt LAGB consists of pyramidal dislocations always has the largest GBE, while that with array of prismatic dislo- cations has the smallest one in the whole range. The Peierls stress of dislocation in tilt LAGB is nearly unchanged, the same as that of single dislocation. This work is useful for further study of dissociated dislocation, solute segregation, precipitate nucleation in tilt LAGB and its interaction with single dislocations.
基金financially supported by the National Natural Science Foundation of China(Nos.52071316,51771206 and 51571198)K.C.Wong Education Foundation(No.GJTD-2020-09)。
文摘The movement or dissociation of dislocations is signifi cantly important for better understanding the plastic deformation mechanisms and mechanical properties of metals.It is commonly believed that a dislocation<110>/2 in Au is easy to dissociate into a pair of Shockley partial dislocations<112>/6 due to low stacking fault energy(SFE).Contrary to this prevailing perception,the present atomistic modeling demonstrates that this reaction could be completely suppressed when dislocations<110>/2 are grouped into tilt walls,consistent with our experimental observations.Such phenomenon is actually the extreme case accompanying with the variation of Burgers vectors of partials with tilt angle,as revealed by a series of simulations,from which it is clearly seen that the Burgers vectors of partials deviate considerably from that of Shockley partials,enormously depending on the tilt angle.Our fi ndings could facilitate a better understanding on many phenomena and properties of face-centered cubic metals(FCC).
