Laser-shock-induced microstructural changes and a comparison with explosive-shock-induced phenomena in metals: Field-ion and electron microscopic studies

Annealed etched molybdenum and tungsten wires were field evaporated to perfection in a specially designed field-ion microscope through which a laser beam could be focused onto the perfect metal emission end form or along the wire shank. Irradiation utilizing a Q-switched laser at fluences between 22 and 35 J/cm2 produced residual effects ranging from increasing numbers of lattice vacancies and vacancy clusters to massive deformation, cavitation and spallation, and melting. The results of increasing vacancy concentration with increasing laser fluence for molybdenum and tungsten were compared to similar observations in explosively shock-loaded molybdenum in concluding that laser shocking can produce residual effects approximately up to several hundred kbar peak pressure. Laser irradiation of electron transparent molybdenum foils also confirmed the attendant features of laser irradiation including vaporization, melting, and shock-induced spallation by direct observations in the transmission electron microscope. Dislocation substructures identical to those observed following explosive shock loading of molybdenum were also observed in the laser-irradiated molybdenum foils.