Scaling Spark Plasma Sintered (SPS) Ultrafine Grain Tungsten for Advanced Nuclear Fusion Reactor Plasma-Facing Components
This project worked to address the lack of robust, reliable plasma facing material solutions for future nuclear fusion reactors. Tungsten is currently one of the top choices due to its high melting temperature, excellent thermal conductivity, and high sputter threshold. However, components produced via current manufacturing technologies suffer from embrittlement, recrystallization, and erosion from exposure to high heat and particle flux. This work utilizes spark plasma sintering of tungsten with ZrC to develop a fine-grain tungsten material solution with superior mechanical properties to monolithic tungsten. Refinement of processing parameters and initial powder mixtures was used to achieve this goal, with ZrC dispersion strengthening also aimed at maintaining microstructure and mechanical properties after severe thermal cycling. A variety of samples were produced in this work using both conventional and deformable punches. Maximum temperature, temperature ramp rate, and W powder size were the primary variables in the conventional setup, with pressure also being varied at lower temperatures with the deformable punch. The deformable punch was utilized as a potential means of achieving lower sintering temperatures and finer grain sizes taking advantage of shear flow within the sample. Grain size, density, and hardness were characterized. It was found that faster temperature ramp rates resulted in significantly larger grain sizes than slower ones. Neither maximum temperature nor ramp rate significantly impacted the density of samples created with traditional punches, however, the maximum temperature and pressure did significantly increase the hardness of samples created with deformable punches. For traditional punches, grain size and hardness were fairly consistent radially until from the center to near the edge, with poor densification occurring at the extreme edge. Large enough samples manufactured in this way could be machined down to produce uniform products, such as reactor wall tiles. Similar radial grain size behavior was observed in deformable punch samples at 500 MPa, though greater variability in both grain size and hardness was observed at 750 MPa likely due to greater shear deformation, which was clearly observed through optical microscopy. The effect of the initial tungsten powder size also played a significant role in hardness, with ~2x increase in the 50 nm samples compared to 500 nm samples with the same sintering conditions. Time-Domain Thermoreflectance was also attempted to measure thermal conductivity. This technique was chosen due to its high accuracy, however, the sensitivity to sample preparation proved difficult and analysis was unreliable. An alternative technique will be utilized in future work to determine whether thermal conductivity of this fine-grain dispersion-strengthened tungsten is affected by the inclusion of ZrC.
- Research Organization:
- Energy Driven Technologies LLC
- Sponsoring Organization:
- USDOE Office of Science (SC), Fusion Energy Sciences (FES)
- DOE Contract Number:
- SC0020690
- OSTI ID:
- 1807641
- Type / Phase:
- STTR (Phase I)
- Report Number(s):
- DOE-Editekk-20690
- Country of Publication:
- United States
- Language:
- English
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