Deciphering the role of second phase precipitates on early-stage surface morphology development of dispersion-strengthened W alloys under low energy He irradiation

Abstract

Abstract Tungsten is the material of choice for plasma-facing components in the divertor region of future plasma-burning tokamak fusion reactors. However, under low energy helium irradiation at elevated temperatures, significant surface morphology changes are expected, including pores, blisters, and fuzz. Dispersion-strengthened tungsten materials with small additions of transition metal carbide dispersoids have been proposed as an alternative to pure tungsten, as they have shown enhanced thermomechanical properties and possible radiation damage tolerance. However, their response to low energy helium irradiation has yet to be fully elucidated. In this work, dispersion-strengthened tungsten alloys containing 1–10 wt.% tantalum carbide, titanium carbide, or zirconium carbide were exposed to 250 eV helium ions at 600 and 800 °C to a 1 × 1020 cm−2 fluence to understand the early-stage irradiation response to helium bombardment. At 600 °C, nanostructuring is only observed on titanium carbide particles. As the temperature is raised to 800 °C, pores and ripples were developed on tungsten grains for all samples; fiber-form structures and isolated tendril growth is observed only on titanium carbide particles. Minimal surface morphology changes were observed on tantalum carbide and zirconium carbide particles. X-ray photoelectron spectroscopy of the alloyed specimens post-irradiation at 800 °C indicates the formation of zirconium and titanium oxides on the surface. Potential thermodynamic, sputtering, and composition-based formation mechanisms behind the novel nanostructuring and chemistry changes of the complex materials are discussed.