Advanced Self-Passivating Alloys for an Application under Extreme Conditions

Abstract

Self-passivating Metal Alloys with Reduced Thermo-oxidation (SMART) are under development for the primary application as plasma-facing materials for the first wall in a fusion DEMOnstration power plant (DEMO). SMART materials must combine suppressed oxidation in case of an accident and an acceptable plasma performance during the regular operation of the future power plant. Modern SMART materials contain chromium as a passivating element, yttrium as an active element and a tungsten base matrix. An overview of the research and development program on SMART materials is presented and all major areas of the structured R&D are explained. Attaining desired performance under accident and regular plasma conditions are vital elements of an R&D program addressing the viability of the entire concept. An impressive more than 104-fold suppression of oxidation, accompanied with more than 40-fold suppression of sublimation of tungsten oxide, was attained during an experimentally reproduced accident event with a duration of 10 days. The sputtering resistance under DEMO-relevant plasma conditions of SMART materials and pure tungsten was identical for conditions corresponding to nearly 20 days of continuous DEMO operation. Fundamental understanding of physics processes undergone in the SMART material is gained via fundamental studies comprising dedicated modeling and experiments. The important role of yttrium, stabilizing the SMART alloy microstructure and improving self-passivating behavior, is under investigation. Activities toward industrial up-scale have begun, comprising the first mechanical alloying with an industrial partner and the sintering of a bulk SMART alloy sample with dimensions of 100 mm × 100 mm × 7 mm using an industrial facility. These achievements open the way to further expansion of the SMART technology toward its application in fusion and potentially in other renewable energy sources such as concentrated solar power stations.

Tooling in Spark Plasma Sintering Technology: Design, Optimization, and Application

“…The application of this die was the sintering of 100 × 100 × 7 mm 3 tiles from a tungsten alloy used for the protection of the first wall in a fusion reactor. [ 6 ] Beside the reduction of die loading, the split die enables the easy extraction of the sintered tiles from the tool. However, its application requires additional time and costs for die manufacturing and the tooling assembling/disassembling before and after sintering, thus complicating the exploitation.…”

“…Despite the problems mentioned above, the literature provides examples of FAST/SPS sintering of parts with various single‐level configurations, such as rectangular plates, hollow cylinders, and thin gears. [ 6,9,10 ]…”

Microstructures and Antioxidation of W Self-Passivating Alloys: Synergistic Effect of Yttrium and Milling Time

“…Following isothermal oxidation, a protective layer of Cr 2 O 3 with a thickness ranging from 100 to 300 nm was detected on the surface. The alloy film exhibited a low parabolic oxidation rate, which was over five orders of magnitude lower than that of pure tungsten at 1273 K [12][13][14]. Prado et al used a brazing technique to join a W-Cr-Y alloy to Eurofer steel with a 50 µm thick Cu interlayer, achieving high quality joints in terms of metallic continuity and strength [15].…”