Industry News | contents page | news | events | advertisers’ index | email | Pure and doped tungsten produced by Powder Injection Moulding for nuclear fusion power plants A research project carried out within the framework of the European Fusion Development Agreement has been investigating the production by Powder Injection Moulding of small prototype plates from pure tungsten (W) and doped tungsten for potential applications in future fusion power plants. The research project involves partners from the Institute of Applied Materials, Karlsruhe University of Technology (KIT), Germany; Department of Materials, University of Oxford, UK; Department of Materials, Imperial College London, UK; Max-Planck-Institut für Plasmaphysik, Garching, Germany; Plansee SE, Reutte, Austria and the Institute for Energy Research at Forschungsinstitut Jülich, Germany. The results of microstructure, mechanical, thermal and oxidation testing for pure W and doped W samples produced by PIM are outlined in the paper “Mechanical and Microstructural Investigations Powder W Particle size (FSSS) 1.0–2.0 μm of Tungsten and Doped Tungsten Materials Produced via Powder Injection Molding” by Steffen Antusch (KIT Karlsruhe) and research partners in the open access Journal of Nuclear Materials and Energy Nos. 3-4, July-August 2015, pp 22-31. Comparisons are made with similar materials produced by conventional swaging, rolling or forging plus machining. The authors stated in the paper that the PIM process using simply mixed powders and binder is seen as a cost effective alternative to more expensive mechanically alloyed W materials for the mass production of complex geometries having good thermal shock, thermal fatigue and oxidation performance. The PIM process can also be used to join W and W doped materials without the need for additional brazing or welding. The objective was therefore to develop Prepared composition Sintering Temperature (°C) Theoretical density (%T.D.) (PW1): Pure W 1800 < 96.0 (PW2): Pure W 2400 98.8 (PW3): Pure W 2600 99.0 Y2O3 < 1.50 μm (PO1): W-2Y2O3 (8.1 vol.%Y2O3) 2400 < 98.9 La2O3 < 2.50 μm (PO2): W-2La2O3 (5.7 vol.%La2O3) 2400 < 98.7 < 50 nm (PC1): W-1TiC (3.8 vol.%TiC) 2400 98.8 (PC2):W-2TaC (2.7 vol.%TaC) 2400 < 98.6 (PC3):W-8TaC (10.7 vol.%TaC) 2400 < 98.5 TiC TaC < 1.0 μm Table 1 Tungsten and doping powder compositions, particle sizes, sintering temperature and theoretical density after sintering. (From paper by S. Antusch et al, Journal of Nuclear Materials and Energy, No. 3-4, July-August 2015, pp 21-30) 28 Powder Injection Moulding International December 2015 new W materials for PIM production and to investigate their properties. As an alternative to using mechanical alloying to produce the doped W powders, the researchers used simple mixing of the pure W powders with oxide doping materials La2O3 and Y2O3, and carbide doping materials TiC and TaC. The doping materials are said to act as grain growth inhibitors. The particle sizes and compositions used in the tests are shown in Table 1. Following mixing the powders are dried at 80°C to remove moisture and then dry mixed with a polyolefine binder (50vol%) in a kneader to produce a homogeneous and agglomerate-free feedstock. Debinding the injection moulded parts removes the binder, impurities such as O and C and also releases the high residual stresses in the parts created by injection moulding. The parts are finally sintered in dry hydrogen for 2 hrs at temperatures shown in Table 1. The density after sintering was found to be as high as ~99% T.D, with a linear shrinkage during sintering of nearly 20%. The pure W samples sintered at 1800°C were found to have lower density <96% T.D., a small grain size and many pores indicating that this temperature was too low. The pure W sample sintered at 2600°C shows very large grains – a consequence of too high a sintering temperature. For all doped materials the embedded oxide and carbide particles are homogeneously embedded around the tungsten grain boundaries and act as grain growth inhibitor. It was reported that only the TaC doped materials showed agglomeration of the TaC particles in the several micrometre range. The best results (microstructure, density and mechanical testing) for pure W were found at sintering temperature of 2400°C. Fig. 1 compares the properties of pure PIM W with rolled W produced by Plansee. The rolled W was found to show a very high stress level, but in comparison to the pure PIM W less strain to failure indicating limited ductility in the rolled material. All © 2015 Inovar Communications Ltd Vol. 9 No. 4