In this paper we examine the effect on the determination of boundary length per unit area of the stepped nature of boundaries in orientation maps derived from electron back-scatter diffraction data.A correction factor...In this paper we examine the effect on the determination of boundary length per unit area of the stepped nature of boundaries in orientation maps derived from electron back-scatter diffraction data.A correction factor is derived for isotropic microstructures.Two measures based on length per unit area for the determination of the cross-link boundary spacing in high strain deformation microstructures are then compared.A geometric method based on subtraction of the contribution to the length per area of the lamellar boundaries gives the best results,though in some cases a method based on boundary misorientation angles may be preferred.展开更多
The observation on emitting dislocations from grain boundaries by TEM during Cu elongation has been performed. It is shown that there exists the 'ledge' at the grain boundaries in fee pure Cu, which is able to...The observation on emitting dislocations from grain boundaries by TEM during Cu elongation has been performed. It is shown that there exists the 'ledge' at the grain boundaries in fee pure Cu, which is able to emit dislocations into grain under action of stress.展开更多
The effect of strain and drawing temperature on the evolution of microstructure and fiber textures of aluminum wiresdrawn at room temperature and cryogenic temperature was investigated by TEM and EBSD observations.The...The effect of strain and drawing temperature on the evolution of microstructure and fiber textures of aluminum wiresdrawn at room temperature and cryogenic temperature was investigated by TEM and EBSD observations.The results show that lowangle boundaries frequency increases and high angle boundaries frequency decreases with strain increasing when the strain is low.Athigh strain,most of grain and dislocation boundaries are parallel to the drawn direction and low angle boundaries frequencydecreases and high angle boundaries frequency increases with strain increasing.The decrease of deformation temperature leads tomicrostructure finer and low angle boundaries frequency increasing.Texture analysis indicates that volume fraction of complextexture component decreases with strain increasing and a mixture of?111?and?100?fiber texture forms at high strain.?111?is stableat low strains but?100?becomes stable at high strain.The decrease of temperature can enhance the stability of?111?orientation athigh strain.展开更多
The hot deformation of an Al-Cu-Mg alloy was studied in the two temperature ranges (room temperature-300℃ and 400℃-480℃). The rate-independent flow curves are typical of elasto-plastic response with significant wor...The hot deformation of an Al-Cu-Mg alloy was studied in the two temperature ranges (room temperature-300℃ and 400℃-480℃). The rate-independent flow curves are typical of elasto-plastic response with significant work hardening followed by strain softening below 300℃. Similar dislocation structures with high density tangled into grain interiors were observed by TEM, which suggests that the process of obstacles arresting mobile dislocations results in this macroscopically rate-independence. At 400-480℃, all rate dependent flow behaviors characterized by a continuous softening after an initial work hardening at a small plastic strain show large tensile elongations. Long dislocation segments around the second phases infer their good mobility to climb across obstacles. Grain boundary morphology observed by TEM suggests that the capacity of the grain boundaries to absorb the dislocations sensitively accounts for the rate-dependent mechanical properties.展开更多
Deformation twinning serves as an important mode of plastic dissipation processes in nanoscale body-centered cubic(BCC)metals,but its origin and spatio-temporal features are mysterious.Here,applying in situ tensile ex...Deformation twinning serves as an important mode of plastic dissipation processes in nanoscale body-centered cubic(BCC)metals,but its origin and spatio-temporal features are mysterious.Here,applying in situ tensile experiments,we report a strong size effect on mediating the twinning behaviors and twin boundary(TB)-dislocation interaction mechanisms in BCC iron(Fe)nanowires(NWs).There exists a critical diameter(d)of∼2.5 nm,above which the deformation twinning rather than dislocation slip dominates the plasticity.Unlike the traditional reflection TBs,the intermediate isosceles TBs are consis-tently observed as mediated by the 1/12<111>partial dislocations.Moreover,we uncover two distinct TB-related deformation mechanisms,including twin variant re-orientation and TB cracking for NWs with d<17 nm and d>17 nm,respectively.Further molecular dynamics and statics simulations provide the basic underlying mechanisms for size-dependent plasticity,which have been largely overlooked in previous experimental investigations.Our findings highlight the importance of grain size in mediating the deformation behaviors in Fe,serving as possible guidance for exploring single-crystalline and poly-crystalline Fe-based materials(e.g.steel)with optimized mechanical performance.展开更多
Clock rolling was developed to make defor- mation microstructure homogenize in high-purity Ta. The substructure of deformed Ta was revealed by electron back-scatter diffraction (EBSD) technique aided with triple foc...Clock rolling was developed to make defor- mation microstructure homogenize in high-purity Ta. The substructure of deformed Ta was revealed by electron back-scatter diffraction (EBSD) technique aided with triple focused ion beam (FIB). The results indicate that the triple FIB method can produce a mirror surface required by EBSD analysis. The clock rolling works well for the homogenization of deformed microstructure. Particularly, the local stored energy in { 111 } orientated grains is largely reduced by clock rolling, whereas it is enhanced in {100} orientated grains because of the occurrence of grain subdivision.展开更多
The effects of large strain and strain path reversal on the deformation microstructure evolution in austenite below the recrystallisation temperature were studied by hot torsion using a non-transforming Fe-30wt%Ni mod...The effects of large strain and strain path reversal on the deformation microstructure evolution in austenite below the recrystallisation temperature were studied by hot torsion using a non-transforming Fe-30wt%Ni model austenitic alloy.Results show that the high angle boundaries (HABs) can be generated by both microstructure mechanism through dislocation accumulation and texture mechanism via subgrain rotation.However,multiple strain path reversals lead to less well-developed HABs in the original grains compared to single reversal deformed to the same amount of total accumulative strain.This effect is attributed to the subgrain rotation mechanism being less effective at small strains.In comparison,the same hot torsion tests were conducted using a microalloyed steel at a temperature between Ae 3 and Ar 3.After single strain path reversal,substantial deformation-induced austenite-to-ferrite phase transformation was observed.Meanwhile,a test with multiple strain path reversals but with the same total strain produces much lower levels of strain-induced ferrite formation.This difference is correlated to the observations made in the Fe-30wt%Ni model alloy.It is believed that the different amount of strain-induced ferrite originated from the different levels of strain-induced HABs within the austenite which act as ferrite nucleation sites.展开更多
基金Supported by the National Natural Science Foundation of China(No.50371041 and No.50571049)
文摘In this paper we examine the effect on the determination of boundary length per unit area of the stepped nature of boundaries in orientation maps derived from electron back-scatter diffraction data.A correction factor is derived for isotropic microstructures.Two measures based on length per unit area for the determination of the cross-link boundary spacing in high strain deformation microstructures are then compared.A geometric method based on subtraction of the contribution to the length per area of the lamellar boundaries gives the best results,though in some cases a method based on boundary misorientation angles may be preferred.
文摘The observation on emitting dislocations from grain boundaries by TEM during Cu elongation has been performed. It is shown that there exists the 'ledge' at the grain boundaries in fee pure Cu, which is able to emit dislocations into grain under action of stress.
基金Projects(51471123,51171135)supported by the National Natural Science Foundation of ChinaProjects(2012K07-08,2013KJXX-61)supported by the Natural Science Foundation of Shaanxi Province,ChinaProject(2013JC14)supported by the Industrialization Program of Shaanxi Province,China
文摘The effect of strain and drawing temperature on the evolution of microstructure and fiber textures of aluminum wiresdrawn at room temperature and cryogenic temperature was investigated by TEM and EBSD observations.The results show that lowangle boundaries frequency increases and high angle boundaries frequency decreases with strain increasing when the strain is low.Athigh strain,most of grain and dislocation boundaries are parallel to the drawn direction and low angle boundaries frequencydecreases and high angle boundaries frequency increases with strain increasing.The decrease of deformation temperature leads tomicrostructure finer and low angle boundaries frequency increasing.Texture analysis indicates that volume fraction of complextexture component decreases with strain increasing and a mixture of?111?and?100?fiber texture forms at high strain.?111?is stableat low strains but?100?becomes stable at high strain.The decrease of temperature can enhance the stability of?111?orientation athigh strain.
文摘The hot deformation of an Al-Cu-Mg alloy was studied in the two temperature ranges (room temperature-300℃ and 400℃-480℃). The rate-independent flow curves are typical of elasto-plastic response with significant work hardening followed by strain softening below 300℃. Similar dislocation structures with high density tangled into grain interiors were observed by TEM, which suggests that the process of obstacles arresting mobile dislocations results in this macroscopically rate-independence. At 400-480℃, all rate dependent flow behaviors characterized by a continuous softening after an initial work hardening at a small plastic strain show large tensile elongations. Long dislocation segments around the second phases infer their good mobility to climb across obstacles. Grain boundary morphology observed by TEM suggests that the capacity of the grain boundaries to absorb the dislocations sensitively accounts for the rate-dependent mechanical properties.
基金supported by the National Natural Science Foundation of China (Nos.52071237,12074290,51871169,52101021,and 12104345)the Natural Science Foundation of Jiangsu Province (No.BK20191187)+1 种基金the Young Top-notch Talent Cultivation Program of Hubei Province,the Science and Technology Program of Shenzhen (No.JCYJ20190808150407522)the China Postdoctoral Science Foundation (No.2019M652685).
文摘Deformation twinning serves as an important mode of plastic dissipation processes in nanoscale body-centered cubic(BCC)metals,but its origin and spatio-temporal features are mysterious.Here,applying in situ tensile experiments,we report a strong size effect on mediating the twinning behaviors and twin boundary(TB)-dislocation interaction mechanisms in BCC iron(Fe)nanowires(NWs).There exists a critical diameter(d)of∼2.5 nm,above which the deformation twinning rather than dislocation slip dominates the plasticity.Unlike the traditional reflection TBs,the intermediate isosceles TBs are consis-tently observed as mediated by the 1/12<111>partial dislocations.Moreover,we uncover two distinct TB-related deformation mechanisms,including twin variant re-orientation and TB cracking for NWs with d<17 nm and d>17 nm,respectively.Further molecular dynamics and statics simulations provide the basic underlying mechanisms for size-dependent plasticity,which have been largely overlooked in previous experimental investigations.Our findings highlight the importance of grain size in mediating the deformation behaviors in Fe,serving as possible guidance for exploring single-crystalline and poly-crystalline Fe-based materials(e.g.steel)with optimized mechanical performance.
基金supported by the National Natural Science Foundation of China (No. 51301212)the Major National Science and Technology Projects of China (No. 2011ZX02705)+1 种基金the Chongqing Science and Technology Commission in China (No. 2012jjA50023)the Fundamental Research Funds for the Central Universities (No. CDJZR11130010)
文摘Clock rolling was developed to make defor- mation microstructure homogenize in high-purity Ta. The substructure of deformed Ta was revealed by electron back-scatter diffraction (EBSD) technique aided with triple focused ion beam (FIB). The results indicate that the triple FIB method can produce a mirror surface required by EBSD analysis. The clock rolling works well for the homogenization of deformed microstructure. Particularly, the local stored energy in { 111 } orientated grains is largely reduced by clock rolling, whereas it is enhanced in {100} orientated grains because of the occurrence of grain subdivision.
文摘The effects of large strain and strain path reversal on the deformation microstructure evolution in austenite below the recrystallisation temperature were studied by hot torsion using a non-transforming Fe-30wt%Ni model austenitic alloy.Results show that the high angle boundaries (HABs) can be generated by both microstructure mechanism through dislocation accumulation and texture mechanism via subgrain rotation.However,multiple strain path reversals lead to less well-developed HABs in the original grains compared to single reversal deformed to the same amount of total accumulative strain.This effect is attributed to the subgrain rotation mechanism being less effective at small strains.In comparison,the same hot torsion tests were conducted using a microalloyed steel at a temperature between Ae 3 and Ar 3.After single strain path reversal,substantial deformation-induced austenite-to-ferrite phase transformation was observed.Meanwhile,a test with multiple strain path reversals but with the same total strain produces much lower levels of strain-induced ferrite formation.This difference is correlated to the observations made in the Fe-30wt%Ni model alloy.It is believed that the different amount of strain-induced ferrite originated from the different levels of strain-induced HABs within the austenite which act as ferrite nucleation sites.