Microscopic mechanisms of melting, resolidification and photomechanical damage/spallation occurring under extreme superheating/undercooling/deformation rate conditions realized in short pulse laser processing are investigated in a computational study performed with a hybrid atomistic-continuum model [1]. The model combines classical molecular dynamics method with a continuum description of the laser excitation and subsequent relaxation of the conduction band electrons.
The kinetics and mechanisms of melting are investigated in simulations of laser interaction with free-standing Ni and Au films [1] and bulk targets [3]. Two competing melting mechanisms, homogeneous nucleation of liquid regions inside the crystalline material and propagation of melting front(s) from external surface(s), are found to be strongly affected by the dynamics of the relaxation of the laser-induced stresses.
The evolution of photomechanical damage is investigated in large-scale simulations of laser spallation of Ni targets, where an ejection of a thin liquid layer is observed. Photomechanical damage is found to take place in two stages, the initial stage of void nucleation and growth followed by the void coarsening, coalescence and percolation [3].
[1] D. S. Ivanov and L. V. Zhigilei, Phys. Rev. B 68, 064114, 2003.
[2] D. S. Ivanov and L. V. Zhigilei, Phys. Rev. Lett. 91, 105701, 2003.
[3] E. Leveugle, D. S. Ivanov, and L. V. Zhigilei, Appl. Phys. A, in press.
Animated sequences of snapshots from molecular dynamics simulations of laser melting and spallation can be found at
http://www.faculty.virginia.edu/CompMat/melting/animations/
http://www.faculty.virginia.edu/CompMat/spallation/animations/
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