Features of Metal Destruction under Pulsed Laser and Beam-Plasma Exposure

Abstract

The features of the destructive effect on metal materials have been studied at high pressures generated in two similar conditions, namely, upon irradiation of the target samples with pulsed laser radiation and beam-plasma flows created in plasma focus (PF) installations. In both cases, similar parameters of radiation-heat treatment were set: power density q ~ 1010–1011 W/cm2 and pulse duration τ ~ 10–100 ns. It has been shown that the double exposure to laser radiation of vanadium and molybdenum thin samples with the thickness of 0.3 and 0.1 mm, respectively, leads to formation of molten zones in the materials that have deep craters inside. The craters extend over the entire thickness of the samples, on the back side of which the recesses end up with holes with diameters of ~0.1 mm for V and 0.2 mm for Mo. In a tungsten sample 0.2 mm thick, the depth of the craters in the molten zone is smaller than its thickness, but there are microcracks on the back of the sample. On the basis of numerical estimates of the process under study, it has been suggested that the observed effects are associated with the creation of high pressure zones of ~1–10 GPa in the irradiated targets, localized in microregions of radius r ~ 0.1 mm. In these zones, the high pressure behavior of the solid phase of the target materials with the tensile strength magnitude σB ≤ 1 GPa (V, Mo, W) is similar to the behavior of liquid. The pseudo-liquid phase of the material is displaced from the center of the crater, where the pressure is maximal, to its peripheral region of low pressure with the subsequent release of matter from the target through the irradiated surface at speed of ~103 m/s. In experiments using the PF, the mechanism responsible for the formation of craters when a powerful pulsed laser radiation is applied to the target is not realized owing to the different nature of the distribution of the absorbed energy density in the surface layer of the irradiated sample. The region in which the energy is absorbed during the implantation of particles into the material is determined mainly by the average energy and the diameter of the ion beam (Еi ≈ 100 keV, d ~ 2–10 mm) and exceeds the corresponding impact region obtained under laser irradiation by one to two orders of magnitude.