Atomistic simulation study of tensile deformation in bulk nanocrystalline bcc iron  

作　　者：YUAN FuPing 

机构地区：[1]State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China

出　　处：《Science China(Physics,Mechanics & Astronomy)》2012年第9期1657-1663,共7页中国科学：物理学、力学、天文学（英文版）

基　　金：supported by the National Basic Research Program of China (Grant Nos. 2012CB932203 and 2012CB937500);the National Natural Science Foundation of China (Grants No. 11002151,10721202and 11072243)

摘　　要：In the present work,the mechanical properties of bulk nanocrystalline(NC) bcc Fe under tensile deformation have been studied by molecular dynamics(MD) simulations.Average flow stress was found to decrease with grain refinement below 13.54 nm,indicating a breakdown in the Hall-Petch relation.A change from grain boundary(GB) mediated dislocation activities to GB activities may be a possible explanation of the breakdown in the Hall-Petch relation.The results also indicate that the average flow stress increases with increasing strain rates and decreasing temperatures.Stress induced phase transformations were observed during the tensile deformation of NC Fe,and such phase transformations were found to be reversible with respect to the applied stress.The maximum fraction of the cp atoms was also found to increase with increasing applied stress.Significant phase transformation occurred in the stacking fault zone due to dislocation activities for large grain size(13.54 nm),while significant phase transformation occurred in the GBs due to GB activities for small grain size(3.39 nm).At deformation temperature of 900 K and above,no apparent phase transformation occurred because all atoms at GBs and grain interior could easily rearrange their position by thermal activation to form local vacancies/disordered structures rather than ordered close packed(cp) structures.In the present work, the mechanical properties of bulk nanocrystalline （NC） bcc Fe under tensile deformation have been stud- ied by molecular dynamics （MD） simulations. Average flow stress was found to decrease with grain refinement below 13.54 nm, indicating a breakdown in the Hall-Petch relation. A change from grain boundary （GB） mediated dislocation activities to GB activities may be a possible explanation of the breakdown in the Hall-Petch relation. The results also indicate that the av- erage flow stress increases with increasing strain rates and decreasing temperatures. Stress induced phase transformations were observed during the tensile deformation of NC Fe, and such phase transformations were found to be reversible with respect to the applied stress. The maximum fraction of the cp atoms was also found to increase with increasing applied stress. Significant phase transformation occurred in the stacking fault zone due to dislocation activities for large grain size （13.54 nm）, while sig- nificant phase transformation occurred in the GBs due to GB activities for small grain size （3.39 nm）. At deformation temper- ature of 900 K and above, no apparent phase transformation occurred because all atoms at GBs and grain interior could easily rearrange their position by thermal activation to form local vacancies/disordered structures rather than ordered close packed （cp） structures.

关 键 词：molecular dynamics simulation phase transformation dislocation activities grain boundary diffusion IRON 

分 类 号：TQ340.651[化学工程—化纤工业] O346.1[理学—固体力学]