Composite Materials for Nuclear Applications: Tungsten
Sponsored by: TMS Structural Materials Division, TMS: Composite Materials Committee, TMS: Nuclear Materials Committee
Program Organizers: Anne Campbell, Oak Ridge National Laboratory; Dong Liu, University of Oxford; Rick Ubic, Boise State University; Lauren Garrison, Commonwealth Fusion Systems; Peng Xu, Idaho National Laboratory; Johann (Hans) Riesch, Max Planck Institute for Plasma Physics
Wednesday 8:30 AM
March 17, 2021
Room: RM 52
Location: TMS2021 Virtual
Session Chair: Lauren Garrison, Oak Ridge National Laboratory; Johann Riesch, Max Planck Institute for Plasma Physics
8:30 AM Invited
Tungsten-based High and Medium Entropy Alloys and Composites for Nuclear Applications: Owais Waseem1; Ho Jin Ryu2; 1MIT PSFC; 2KAIST, Korea
Tungsten-based alloys and composites have been studied for fusion plasma facing materials in order to improve the physical properties of pure tungsten under extreme environments. Recently, the concept of high entropy alloys or concentrated solid solution alloys was proposed for the irradiation resistant matrix materials. High entropy alloy based composites were designed, fabricated by using powder metallurgy processing in order to characterize the thermal properties, mechanical properties, irradiation resistance and oxidation properties. The effects of the composition of the high and medium entropy alloys and the configuration of pure tungsten-based reinforcement have been analyzed.
9:00 AM Invited
Tungsten Fibre-reinforced Copper – A High-Conductivity, High-Strength Composite Material for Plasma-facing Component Applications: Alexander Von Mueller1; Bernd Böswirth1; Henri Greuner1; Rudolf Neu1; Udo Siefken2; Eliseo Visca3; Jeong-Ha You1; 1Max-Planck-Institut für Plasmaphysik; 2Louis Renner GmbH; 3ENEA Frascati
In future deuterium-tritium magnetic confinement fusion reactors plasma-facing components (PFCs) have to sustain intense particle, heat and neutron fluxes. This is especially true for PFCs in the divertor region where materials with high thermal conductivity have to be applied in order that steady-state heat fluxes in the range of 10-20 MW/m2 can be exhausted reliably. Currently favoured heat sink materials with regard to highly loaded PFCs are copper alloys mainly due to their high conductivity. However, the deterioration of the mechanical properties of such materials under fusion neutron irradiation - embrittlement at lower and softening at elevated operating temperatures - represents a significant issue. Against this background, development work regarding tungsten fibre-reinforced copper (Wf-Cu) composite materials was pursued during recent years. In this context, the contribution will summarise topical results with respect to the performed research activities, including high heat flux tests of Wf-Cu within tungsten monoblock type PFC mock-ups.
9:30 AM Invited
W2C-reinforced Tungsten: A Promising Candidate for DEMO Divertor Material: Petra Jenus1; Aljaz Iveković1; Matej Kocen1; Anze Abram1; Andreja Sestan1; Andrei Galatanu2; Magdalena Galatanu2; Sandra Tarancón3; Elena Tejado3; Jose Ygnacio Pastor3; Marius Wirtz4; Gerald Pintsuk5; Sasa Novak1; 1Jožef Stefan Institute; 2National Institute of Materials Physics; 3Universidad Politécnica de Madrid; 4Institute for Energy and Climate Reseach, Forschungszentrum Juelich GmbH, ; 5Institute for Energy and Climate Reseach, Forschungszentrum Juelich GmbH,
Tungsten is considered as the material of choice for the divertor application of fusion power plants due to its intrinsic thermo-physical properties. However, one main drawback is the recrystallization induced reduction of its mechanical properties at elevated temperatures. Therefore, the aim of the conducted research was to improve the material properties to be able to sustain plasma-facing conditions, especially to be able to resist high thermal loads imposed on the divertor during operation. The reinforcement of tungsten by incorporation of carbide nanoparticles, resulted in a material with a stable microstructure and promising high-temperature behaviour.WC nanoparticles were used as a source for the in-situ formation of W2C inclusions in the W matrix during the thermal treatment of powder mixtures with a field assisted sintering technique (FAST). In addition to thorough microstructural and phase analysis, thermo-mechanical properties at room and elevated temperature, as well as high-heat-flux tests, will be presented.
10:00 AM
Solving the Brittleness Problem of Tungsten - Tungsten Fibre-reinforced Tungsten Composites: Johann Riesch1; Jan Coenen2; Bailey Curzadd1; Maximilian Fuhr1; Lauren Garisson3; Hanns Gietl3; Henri Greuner1; Till Höschen1; Yiran Mao2; Wolfgang Pantleon4; Leonard Raumann2; Daniel Schwalenberg2; Thomas Schwarz-Selinger1; Dmitry Terentyev5; Rudolf Neu1; 1Max Planck Institute für Plasma Physics; 2Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung – Plasmaphysik, Partner of the Trilateral Euregio Cluster (TEC); 3Oak Ridge National Laboratory; 4Technical University of Denmark; 5Belgian Nuclear Research
Due to its unique property combination tungsten materials are the preferred choice for high-heat-flux-loaded areas in future fusion power plants. However, tungsten has a high brittle to ductile transition temperature and is prone to operational embrittlement due to high temperature and/or fast neutron irradiation. Tungsten fibre-reinforced tungsten composites utilize extrinsic mechanisms to improve the fracture toughness and thus mitigate this drawback.In this contribution, we will present the main characteristics and properties of this new composite material. Drawn potassium-doped W wire is used as ductile, high strength fibrous reinforcement. Engineered fibre-matrix interfaces ensure the desired composite behaviour. The tungsten matrix is formed around woven long fibres or randomly orientated short fibres by chemical vapour deposition or powder metallurgy, respectively. A review will be given of the material’s development, starting from the first ideas up to recent high heat flux tests and investigations after neutron irradiation.
10:20 AM
Opportunities for Nanostructured Tungsten Alloys in Composite Fusion Materials: Jason Trelewicz1; Nicholas Olynik1; Wenbo Wang1; David Sprouster1; Chad Parish2; 1Stony Brook University; 2Oak Ridge National Laboratory
Tungsten has emerged as the primary armor material for plasma facing components (PFCs) due to its attractive properties, resistance to sputtering, and chemical compatibility with tritium. Recognizing that embrittlement and thermal conductivity degradation from neutron loading are potentially insurmountable issues for tungsten, advanced tungsten-based alloys and composites are being explored as engineered materials for PFCs. However, in tungsten/tungsten composites, the matrix will still inherently be limited by the same issues plaguing bulk tungsten. In this presentation, we discuss opportunities for nanostructured tungsten alloys designed specifically for the fusion environment as a stable matrix phase of tungsten-based composites. Guided by thermodynamic models of dopant distributions, a ternary system is identified for enhancing stability and manufacturability. Alloys are synthesized via powder metallurgical processing and analyzed using synchrotron x-ray diffraction and small angle x-ray scattering experiments. The benefits of microstructures containing desirable nanoscale compositional heterogeneities are finally discussed for nanostructured tungsten-based composite PFCs.
10:40 AM
Conformal Tungsten Coatings for Cermet Nuclear Fuel Elements: Jonathan Johnson1; Ryan Wilkerson2; Stephen DiPietro3; Scott O'Dell4; Gregory Thompson1; 1University of Alabama; 2NASA Marshall Space Flight Center; 3Exothermics Inc; 4Plasma Processes LLC
Nuclear thermal propulsion (NTP) is being explored for deep space applications as it can reduce total trip time for interstellar travel. One of the concerns for NTP nuclear fuels is the particle-to-particle contact in the cermet creating ‘hot spots’ and promoting additional fissile fuel loss. A mitigation strategy to eliminating these contact points is to provide conformal coatings over the individual fuel particles to promote separation in the final cermet. In this presentation, sputtering is utilized to provide tungsten coatings onto surrogate fuels. The coatings created a 'powdery' morphology that is contributed to repeated coating-to-coating adhesion and subsequent fracture. The coated powders were sintered to determine the coatings effectiveness in promoting particle isolation in the microstructure of the cermet. The use of multiple PVD sputtering targets is also addressed in creating secondary phases that can serve as hydrogen traps.
11:00 AM
Coupled Primary and Secondary Recrystallization in Single Tungsten Fiber-reinforced Tungsten Composites: Umberto Ciucani1; Lea Haus1; Maximilian Fuhr2; Hanns Gietl3; Johann Riesch2; Wolfgang Pantleon1; 1Technical University of Denmark; 2Max-Planck-Institute for Plasma Physics; 3Oak Ridge National Laboratory
Tungsten fiber-reinforced tungsten composites with a tungsten matrix reinforced by heavily drawn tungsten fibers are developed for application in future fusion reactors. During their time in service, the microstructure of the highly deformed fibers will unavoidably be altered by recrystallization occurring at the high operation temperatures, causing degradation of the mechanical properties. To investigate the thermal stability of tungsten fiber-reinforced tungsten composites, pure tungsten has been deposited onto single potassium-doped tungsten wires with and without rare earth oxide interlayers. Specimens of single fiber composites were annealed at different temperatures between 1350 °C and 1400 °C for up to four weeks and investigated by means of electron backscatter diffraction. During annealing, the wires start to recrystallize. Without any interlayer, recrystallization nuclei formed in the wire grew into the surrounding matrix and continued growing there. Oxide interlayers prevented such continued growth, although abnormal growth of some grains occurred in the deposited tungsten.