Molecular Dynamics Analyses of the Femtosecond Laser-induced Grain Boundary Spallation

飛秒雷射誘生晶界剝離之分子動力分析

賴新一(Hsin-Yi Lai) ； 黃培興(Pei-Hsing Huang)

《中國機械工程學刊》 28卷6期 (2007/12) Pp. 577-583

https://doi.org/10.29979/JCSME.200712.0004

摘要

先前以分子動力所模擬雷射誘生熔蝕之研究，大多集中在雷射與完美單晶材料之交互作用，由於忽略實際材料之晶界效應，模擬結果可能導致低估雷射熔蝕之產率與彈射團簇之尺寸分佈。本文應用Lennard-Jones分子動力模擬，首次嘗試研究飛秒脈衝雷射可能誘生之晶界剝離效應，模擬過程針對各種的雷射入射能量密度與吸收係數來描述晶界的結構演化與動力行為反應。模擬結果顯示，吸收係數越大，所誘生震波在靶材內傳播之能量密度越集中，因此，吸收係數足以影響晶界之結構是否發生剝離，並且可以進一步作為控制晶界剝離的重要機制之一。此外，透過估算晶界面剝離之能量，以及針對各種不同光學吸收係數所引發的臨界剝離能率之評估，可以更加了解雷射誘生晶界剝離之微觀機制，經由本文所使用之模型以及晶界效應之考量，可進一步用來提升預測多晶材料之雷射熔蝕深度和彈射團簇尺寸分佈的精確度。

並列摘要

The previous laser-induced ablation researches by using molecular dynamics (MD) simulation are almost focused on the laser interaction with perfect single-crystal matters. The result can therefore lead to underestimate the ablation yields and size distribution of ejecting clusters due to without including the effect of grain boundary. The present model by using standard Lennard-Jones (L-J) MD simulation is firstly attempted to study the possible spallation effect induced by femtosecond pulse laser at grain boundary for polycrystalline materials. Various laser incident energy densities and absorption coefficient are employed to characterize the dynamic behavior and structural evolution of grain boundary. The simulation results indicate that the absorption coefficient can be one of the dominant factors to influence the occurrence and mechanism of structural spallation at grain interface. The interfacial spallation energy is evaluated. The critical spallation thresholds for various absorption coefficients are also identified. The results provide better understanding for laser-induced spallation of grain interface. The model can be also enhanced to promote the accuracy of the prediction of laser-induced ablation depth and size distribution of ejecting clusters through taking into account the effect of grain boundary.

並列關鍵字

molecular dynamics ； pulse laser ； grain boundary ； spallation