Effect of Pulsed Helium Ion and Helium Plasma Flows on Austenitic Chromium–Manganese Steel Preirradiated with Deuterium

Abstract

The effect of sequential action of pulsed helium ion and helium plasma flows on low-activated austenitic 25Cr12Mn20W chromium–manganese steel samples cut from a hexagonal pipe preirradiated with the deuterium ion and deuterium plasma flows in different modes at the Plasma Focus PF-1000 facility has been studied. Two deuterium irradiation modes have been implemented: a relatively soft mode with a power density of q ~ 10⁷–10⁸ W/cm² and a hard mode with q ~ 10⁹–10¹⁰ W/cm² with a pulse length of τ = 100 ns and number N = 4 of pulse discharges in both cases. It has been shown that the effect of the helium ion and helium plasma flows at the PF Vikhr facility with irradiation parameters of q ~ 10⁷–10⁸ W/cm², τ = 100 ns, and N = 15 on the inner surface of a steel pipe sample depends on the mode of its preirradiation with deuterium ion and deuterium plasma flows. In the relatively soft mode of pre-exposure to deuterium ion and deuterium plasma flows with a power density of q ~ 10⁷–10⁸ W/cm², the subsequent pulsed irradiation with helium causes slight changes in the damageability of the surface layer: smoothing of the wavelike surface relief, an increase in pore formation in the surface layer, appearance of microcracks in it, and formation of spherical particles consisting of basic and impurity elements of the steel composition. The presence of niobium deposited from the anode of the PF facility has also been observed. The impact of the helium ions and helium plasma flows on the inner surface of a steel pipe sample after its preirradiation with deuterium ion and deuterium plasma flows in the hard mode at q ~ 10⁹–10¹⁰ W/cm² increases the damageability of the surface layer. Implantation of helium into the material facilitates an increase in the number and size of open cavities (tens of microns) emerging in the surface layer at the stage of preirradiation of the pipe with deuterium, formation of numerous small (up to ~5 μm) bubbles and pores in it, and emergence of spherical particles of different phases on the irradiated surface. An increase in the damageability of the surface layer in the investigated steel sample after its subsequent pulsed irradiation with helium is accompanied by a significant increase in the intensity of erosion of the material as compared with the situation implemented in the softer mode of pre-irradiation of the sample. The enhanced erosion leads to a noticeable decrease in the content of niobium deposited onto the irradiated surface.