Influence of Pulsed Laser Radiation on the Morphology and Surface Properties of Tungsten Implanted with Helium Ions

Abstract

The effect of high-power pulsed laser radiation (LR) generated in the GOS 1001 setup in the Q-modulated mode (with a flux power density q equal to 1 × 10¹⁴ W/m², pulse duration t = 50 ns, and the number of pulses N from 1 to 8 in vacuum) on the structure and microhardness of the surface of tungsten samples in the initial state and after implantation of helium ions (energy of 30 keV, dose of 1.0 × 10²² m^–2, ion flux density of 4.8 × 10¹⁸ m^–2 s^–1, temperature ~500 K) was studied. It was found that the pulsed action of LR on tungsten in the specified mode leads to the appearance of a molten area with a directed splash of metal from the central zone and to the formation of a wavy surface containing drops, influxes, voids, and cracks after crystallization of the melt. The analysis performed by the numerical modeling showed that the observed nature of damage on the irradiated tungsten surface is associated with the occurrence of secondary plasma during the material evaporation, the pressure of which contributes to the melt splashing, but is insufficient to displace the melt with the formation of a crater, as is in the case with vanadium. It was found that, as a result of the combined effect of helium ions and pulsed laser radiation, the morphology of the material surface in the heat-affected zone (HAZ) located directly behind the parapet also changes, where, as it moves away from the center, the area of continuous melting is replaced by a zone in which pores and opened blisters are visible owing to the release of helium implanted in the samples. A slight decrease in the microhardness of the alloy after implantation of helium ions was noted. The microhardness in the molten areas by LR and in the areas adjacent to them also tends to decrease, which may be due to the annealing of original defects as the result of the thermal effect of laser pulses.