Different Behavior between Edge and Screw Dislocations at the .GAMMA./.GAMMA.' Interface of Ni-Based Superalloy: A Molecular Dynamics Study

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  • Ｎｉ基超合金γ／γ′界面における刃状転位とらせん転位挙動の違い：分子動力学による検討
  • Niキ チョウゴウキン ガンマ ガンマ カイメン ニ オケル ハジョウ テンイ ト ラセン テンイ キョドウ ノ チガイ ブンシ ドウリキガク ニ ヨル ケントウ

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Different behaviors between the edge and screw dislocations in the γ/γ'microstructure of Ni-based superalloy are investigated by using molecular dynamics simulations. The simulations are implemented with a slab cell of Ni matrix involving an apex of a cuboidal Ni3A1 precipitate, that mimics a part of the idealized γ/γ' microstructure with about 3 million atoms. Mode II and III type displacements are applied on the cell to nucleate the edge and screw dislocations, respectively, and proceed them toward the precipitate. The edge dislocation decreases its velocity at the γ' precipitate, showing dislocation pinning there, then penetrates it under the force from the follow-on dislocation.The screw dislocation runs through the precipitate without slowdown by shrinking the with between its Shockley partials. Detail investigation of the stress distribution suggests that the constriction is due to interactions between the stress field around the precipitate and the partials : the stress causes repulsive Peach-Koehler force on the leading partial and attractive on the trailing since their edge components have opposite Burgers vectors. In addition to the fact that the strain energy of a screw dislocation is smaller than that of an edge, the constricted screw dislocation makes smaller atomic step on the γ' precipitate than the extended edge dislocation. Thus the screw dislocation easily penetrates the precipitate while the edge is pinned.

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