Atomistic simulation of yield and plastic deformation in bulk nanostructured metals

バルクナノメタルの降伏挙動と塑性変形に関する原子シミュレーション

都留 智仁   ; 青柳 吉輝*; 加治 芳行  ; 下川 智嗣*

Tsuru, Tomohito; Aoyagi, Yoshiteru*; Kaji, Yoshiyuki; Shimokawa, Tomotsugu*

バルクナノメタルなどの結晶粒がきわめて小さい金属では、通常の強化機構を越えて降伏応力は著しく上昇する。また、粗大粒金属と比べて引張・圧縮異方性や、繰り返し変形による異方性が観察される。バウシンガー効果などの繰り返し変形による異方性は多くの微細粒材料に共通であり、引張・圧縮異方性は一部の金属にのみに見られるが、これらの要因は明らかになっていない。そこで、本研究では、複数の結晶粒と転位源を有する三次元多結晶モデルを用いた原子シミュレーションによって、変形時の内部構造の変化から特異な機械特性と材料によって異なる塑性異方性について検討を行った。

The influence of dislocation density on yield strength, which is a key factor in the anomalous deformation behavior in ultrafine-grained (UFG) metals, was investigated by huge scale atomistic simulations. Polycrystalline models with intragulanular Frank-Read sources were constructed to elucidate the relationship between the inter- and intra-granular plastic deformation processes and the mechanical properties. Then the uniaxial tension and compression were applied to the polycrystalline copper. Consequently it was found that Frank-Read sources were activated prior to intergranular dislocation emission, and the yield event of the whole system seems to occur when some dislocation sources activated. The yield stress is strongly influenced by the number of intragranular dislocation sources, i.e., dislocation density. Additionally, the Bauschinger effect of UFG metals is caused by the change in dislocation density in the process of forward and backward deformation.