Experimental characterization and atomistic modeling of interfacial void formation and detachment in short pulse laser processing of metal surfaces covered by solid transparent overlayers
- 329 Downloads
The short pulse laser interaction with metal surfaces covered by solid transparent overlayers is investigated in experiments and atomistic simulations, with a particular aim of revealing the mechanisms responsible for structural modification of the metal–overlayer interfacial regions. Experimental characterization of Al–silica targets modified by single-pulse laser irradiation with the pulse duration of 10 ps reveals the transitions from the generation of extended interfacial voids with internal nanoscale surface roughness to the partial detachment of the overlayer from the metal substrate, and to the cracking/chipping or complete removal of the overlayer as the laser fluence increases. The mechanisms responsible for the appearance, growth, and percolation of the interfacial voids leading to the detachment of the overlayer from the metal substrate are investigated in a large-scale atomistic simulation. The results of the simulation demonstrate that the processes of nucleation and growth of the interfacial voids are driven by the dynamic relaxation of laser-induced stresses proceeding simultaneously with rapid phase transformations and temperature variation in the interfacial region. The growth and coalescence of the interfacial voids results in the formation of liquid bridges connecting the overlayer and the metal substrate, whereas solidification of the transient liquid structures produced by the breakup of the liquid bridges may be responsible for the formation of the nanoscale roughness of the interfacial voids observed in experiments. Computational analysis of the effect of preexisting interfacial voids reveals a complex dynamic picture of the initial expansion and subsequent compaction of the surface region of the metal substrate and suggests a possible scenario for the formation of voids below the metal–overlayer interface.
KeywordsMetal Substrate Laser Fluence Liquid Bridge Melting Front Laser Shock Peening
Financial support for this work was provided by the National Science Foundation (NSF) through Grant CMMI-1301298, the Air Force Office of Scientific Research through Grant FA9550-10-1-0541, and Electro Scientific Industries, Inc. Computational support was provided by the Oak Ridge Leadership Computing Facility (Project MAT048) and NSF through the Extreme Science and Engineering Discovery Environment (Project TG-DMR110090). The authors at ESI thank Motoaki Honda of University of Oregon for kind assistance with SEM measurements.
- 15.J. Cagnoux, F. Longy, Spallation and shock-wave behaviour of some ceramics. J. Phys. Colloq. 49(C3), C3–3 (1988)Google Scholar
- 32.B. Rethfeld, K. Sokolowski-Tinten, D. von der Linde, S.I. Anisimov, Ultrafast thermal melting of laser-excited solids by homogeneous nucleation. Phys. Rev. B 65, 092103 (2002)Google Scholar