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Explosive shock and Q-switched laser exposure of metallic and ceramic materials have produced varied substructures and increased hardness that possibly emphasize the role of the attendant material structures and the nature of the defect substructures that are subsequently obtained. In metallic materials, Q-switched laser exposure is seen to result in extensive heating as well as shock wave passage effect, while the control of temperature in explosive detonation is seen to introduce shock effect and associated defect substructure. For example, explosive shock exposure of Al-Li 8090 alloy is seen to increase hardness, reduce activation energy for subsequent ageing, introduce precipitation, revealing the extensive role defect substructure plays in the ageing kinetics of this alloy. Shock loading of Molydenum at 150 kbar (for 2 μs) increases dislocation loop densities from 5x10/cm to 4x10/cm with 75% of the loop types analyzed being vacancy loops. Irradiations utilizing a Q-switched laser at also of Mo at fluences between 22 and 35 J/cm produced residual effects ranging from increasing numbers of lattice vacancies and vacancy clusters to massive deformation, cavitation, and spallation along with melting. Finally, explosive shock exposure, at various calculated pressures, of Al203, Al203+Zr02, Al203+SiC (whisker), Al203+Zr02+SiC (whisker), showed no significant difference in mechanical properties of hot-pressed Al203+Zr02 composites with regard to shock treatment. Improved mechanical properties were occasionally found in shock-treated and hot-pressed whisker-reinforced alumina, although a direct relationship with shock pressure was not observed. The manuscript summarizes these different studies in delineating the role of shock waves passage in the subsequent material processing. This is an overview of these research projects and fuller details can be found in the cited references. www.witpress.com, ISSN 1743-3509 (on-line) © 2006 WIT Press WIT Transactions on The Built Environment, Vol 87, Structures Under Shock and Impact IX 147 doi:10.2495/SU060151 1 Laser and shock exposure of metallic materials Essentially, all laser interactions with metals involve the absorption of all or a portion of the light energy and its conversion to heat with or without a change in phase of the surface material. For radiation from Q-switched lasers, the interaction with metals has been considerable in terms of the surface rising to the vaporization temperature and vaporization being initiated. As materials recoil against the surface, high-pressure stress waves (or shock waves) can be generated. This pressure pulse raises the boiling point of the underlying material which becomes superheated as more heat is conducted into the interior. In effect, the thermal expansion which follows the rapid absorption of radiant energy at the surface of an elastic solid can propagate a shock wave into the interior. An important feature which distinguishes Q-switched laser interaction from that of a CW laser is the extremely large temperature gradients and the time rates of change of temperature (>10°C/s) involved. Since the production of stress waves in solids using high-powered pulsed lasers is fundamentally a surface phenomenon, the magnitude of those stress waves can be modified by modifications in the target surface conditions. Laser-shock effects should be expected to be fundamentally different from those produced by plane shock waves generated by explosively driven flyer plates and the like because the laser generated shock waves will propagate from a small source region, the impinging laser beam spot, creating a radially attenuating stress pulse, while in conventional shock-loading case, the material is considered to be characterized by a uni-axial strain state which in most instances is not large and allows for a hydrostatic stress approximation [1].

Explosive shock and laser exposure of metallic and ceramic materials