EU-PWI TF meeting, Ljubljana November 2006 Studies of Plasma-Wall Interactions Association IPPLM / EURATOM, Poland Presented by Elzbieta Fortuna Association EURATOM-IPPLM Warsaw University of Technology

EU-PWI TF meeting, Ljubljana November 2006 Selected Research Areas Studies of material erosion and re-deposition on plasma-facing components from the TEXTOR tokamak Novel W-Cu composites Nanomaterials Outline

EU-PWI TF meeting, Ljubljana November 2006 Studies of material erosion and re-deposition on plasma-facing components from the TEXTOR tokamak Work programme: a) Characterization of erosion and re-deposition zones of various graphite PFCs b) Characterization of co-deposits, flakes and dust c) Characterization of plasma-induced damage in high Z metals used as limiters d) Searching for evidence of brittle destruction occurring on PFCs In cooperation with : Alfvén Laboratory, Royal Institute of Technology (KTH), (VR), Sweden Institut für Plasmaphysik, Forschungszentrum Jülich GmbH (FZJ), Germany

EU-PWI TF meeting, Ljubljana November 2006 Characterization of plasma-induced damage in tungsten coatings of graphite limiters Experimental VPS tungsten coatings with a PVD Re/W sandwich interlayer on graphite limiter blocks (EK 98) were studied after the experimental campaign in the TEXTOR tokamak). The limiters were exposed to a variety of plasma operation scenarios in the presence of either boronised or siliconised walls. During some discharges the heat loads to the limiter exceeded 20 MW/m 2 causing the surface temperature rise to above 3600 K (leading to overheating and damage of several limiter blocks). The examination was focused on: micro-structure of the interface layer chemical and phase composition of co-deposited films

EU-PWI TF meeting, Ljubljana November 2006 Structure of VPS-W coating and Re-W interface to carbon Initial structure SEM image of the initial structure of PVD interlayer and distribution of rhenium, tungsten and carbon TEM images of the Re-W layers interface

EU-PWI TF meeting, Ljubljana November 2006 Structure of VPS-W coating and Re-W interface to carbon Overheated part of a coating (σ) SEM image of the degenerated structure of PVD interlayer together with Re and C line scan 25 m Tile side Nano-hardness measurements results VPS tungsten H = 9 GPa W-Re zone H = 24 GPa (under maximum load 40 mN ) Re+W VPS tungsten

EU-PWI TF meeting, Ljubljana November 2006 Material mixing on plasma-facing surfaces XRD pattern showing the phase composition of the plasma-facing surface

EU-PWI TF meeting, Ljubljana November 2006 Conclusions 1. XRD study has proven the co-existence of several major phases in co-deposited films: metallic W, carbides (WC and W 2 C) and boride (W 2 B). Carbon, boron and silicon are the major plasma impurities in co-deposited films on top of the limiter. The content of deuterium ranges from 5x10 14 cm -2 in the overheated area to 1x10 18 cm -2 in carbon-rich films in the deposition zone. 2. In the overheated region the W-Re sandwich interlayer has been transformed into a brittle inter-metallic phase containing wt.% of W. Transverse cracks in the phase layer usually end at the W – Re/W interface. In some cases the cracks propagate along this interface causing delamination. Beneath W-Re layer several micron thick zone with increased carbon concentration were detected.

EU-PWI TF meeting, Ljubljana November 2006 Novel W-Cu composites The main goal of this project is to develop new, modern functionally graded W-Cu composites for application in fusion reactors (divertor). Such composites could be also of interest for electrical contacts, spark erosion electrodes and heat sink materials. Relevance of the project The plasma facing materials (PFM) foreseen for ITER are Be, CFC and tungsten. As a heat sink material the Cu alloy is proposed. The main problem in the development of W/Cu joints is the large difference in the coefficients of thermal expansion (CTE) ( Cu 4 W ) and elastic modulus (E Cu 0.2E W ). This difference generates large stresses at the W/Cu interfaces during manufacturing and/or during operation of PFCs. These stresses may lead to cracking, delamination and a reduced lifetime of the components. FGMs can reduce the thermal stresses and increase lifetime.

EU-PWI TF meeting, Ljubljana November 2006 The arc discharges that take place between the powder particles accelerate mass transport and enhance the process of activation of the powder surface by removing oxides and contaminants. Thanks to the use of capacitors as the source of electric energy, periodically repeated current pulses of a duration of several hundred microseconds and an amplitude of tens kiloamperes are used. The total sintering time is about ten minutes. This method utilizes a pulsed high electric current discharge to heat the powder subjected to pressing. The powder mixture is loaded into a graphite die, between two graphite punches. The powder is heated by the pulse high-current electric discharges generated by discharging of a 300 μF capacitor, charged to a maximum voltage of 10kV. Fabrication technique - Pulse Plasma Sintering

EU-PWI TF meeting, Ljubljana November 2006 Apparatus for pulse plasma sintering Parameters Impulse duration ( s) 600 Maximum pulsed current (kA) 60 Maximum discharge energy (kJ) 15 Maximum impulse frequency (Hz) 2 Maximum discharge voltage (kV) 10 Maximum sample diameter [mm] 50 This technique can be used for sintering of a wide range of materials e. g. metals (tungsten, titanium, iron and its alloys), ceramics (Al 2 O 3, TiN, TiB 2 ) metal- ceramics composites (WC-Co, NiAl-TiC, NiAl-Al 2 O 3 ) as well as for SHS (self propagating synthesis). It enables to receive sinters with density approaching 99% of theoretical in several minutes time Parameters of the pulse plasma sintering apparatus

EU-PWI TF meeting, Ljubljana November m 100 m5 m W-Cu composite/tungsten plate joint Composites microstructure W 75vol.%Cu W 50vol.%Cu

EU-PWI TF meeting, Ljubljana November 2006 PropertiesW-50vol.%CuW-75vol. %Cu Density [g/cm 3 ]13.9 [98.6%TD]11.3 [98.5% TD] Hardness HV UTS [MPa] CTE [1/K] at 500 o C 7x x10 -6 Composites properties

EU-PWI TF meeting, Ljubljana November 2006 Summary The Pulse Plasma Sintering might be a perspective technology for W-Cu composites manufacturing. The W-50vol.%Cu and W-75vol.%Cu composites have been successfully fabricated by this method by sintering at 900 o C for 300s. The results obtained in this study pave the way for sintering gradient composite materials. The first experiments, using the PPS devise to join the composite material to tungsten plate, show that this method could also be used for joining W-Cu and W elements.

EU-PWI TF meeting, Ljubljana November 2006 Application of hydrostatic extrusion for particle and grain size refinement in materials relevant to the fusion technologies The aim of the present project is to describe the thermal stability of fusion relevant materials such as EUROFER 97 processed by hydrostatic extrusion and to determine the factors responsible for thermal stability improvement. The results of the investigations will allow to optimize the material microstructure and the processing route. Eurofer 97

EU-PWI TF meeting, Ljubljana November 2006 Effect of hydrostatic extrusion on mechanical properties and thermal stability of Eurofer 97 Thermal stability of HE processed Eurofer 97 Microhardness vs. true strain

EU-PWI TF meeting, Ljubljana November 2006 Thank you for your kind attention