RESUMEN
Dynamic characteristics of femtosecond laser-generated shockwaves are investigated in ambient air. The experiments are performed using a 360-fs pulsed laser at a wavelength of 1.03 µm, with laser intensities up to 5 × 1014 W/cm2 (corresponding to about five times the air breakdown intensity threshold). Plasma and shockwave generation and propagation are visualized using a time-resolved transmission microscope. The maximum propagation velocity is in the order of Mach 30. By implementing a simple theoretical model, we find an initial pressure loading in the GPa range and shockwave pressure dropping down to MPa following propagation over few micrometers away from focus.
RESUMEN
With the advent of new steel grades, galvanic protection by zinc coating faces a new paradigm. Indeed, enrichment in strengthening elements prone to oxidation, such as Al, Mn, and Si, leads to the formation of oxide films that are poorly wet by zinc. We study herein routes for the improvement of adhesion at the model Zn/α-Al2O3 interface by the addition of metals. As a first step, with the help of ab initio results on the adsorption characteristics of transition metal adatoms at α-alumina surfaces, we establish and rationalize clear trends in both the behavior of metal-alumina interaction strength and the relative thermodynamic stability of configurations with weakly and strongly bound metal adatoms. The reasons for the enhanced binding strength of transition metals, such as Cr, maintained regardless of the precise alumina termination and the surface charge state are pointed out. On these grounds, possible improvements of adhesion under realistic conditions are discussed. It is predicted that enrichment in transition metals, such as Cr, may produce strongly adhesive interfaces that lead to cohesive cleavage.
