Microstructural control of tungsten plates: impacts of potassium concentration and multi-pass rolling on thermal stability

This study systematically investigates the synergistic mechanisms of potassium (K) concentrations (50 ppm vs. 100 ppm) and rolling passes (three passes vs. four passes) on the thermal stability of tungsten-potassium (KW) alloys. The KW alloys were prepared via powder metallurgy and subjected to multi-pass rolling with a total deformation of 65%. The results demonstrate that the alloy doped with 100 ppm K exhibits superior thermal stability after annealing at 1350°C, attributed to the pinning effect of K bubbles at grain boundaries. This significantly inhibits grain coarsening and reduces the migration rate of recrystallized grain boundaries. Compared to four-pass rolling, three-pass rolling under the same deformation level produces a more uniform strain distribution. This not only maintains a high dislocation density but also alleviates local stress concentration, thereby promoting the formation of a homogeneous subgrain structure after annealing. The synergistic effect of 100 ppm K doping and three-pass rolling elevates the recrystallization temperature of the KW alloy to above 1350°C, approximately 100°C higher than that achieved by conventi1onal processes. This “K bubble-strain synergy” strategy optimizes grain size (Hall-Petch effect), dislocation configuration, and bubble stability, significantly enhancing the alloy’s resistance to high-temperature damage. The findings provide new insights for the design of plasma-facing materials (PFMs) in fusion reactors.