Antusch, S.

Commin, L.

Mueller, M.

Piotter, V.

Weingärtner, T.

KITopen

Two component tungsten powder injection molding – An effective massproduction process qq Paper presented at the 2nd IAEA-EC Topical Meeting on Development of New Structural Materials for Advanced Fission and Fusion Reactor Systems, 16–20 April 2012, Joint Research Centre of the European Commission, Ispra (Italy), ⇑ Corresponding author. Tel.: +49 721 608 22553; fax: +49 721 608 22095.E-mail address: steffen.antusch@kit.edu (S. Antusch).Steffen Antusch ⇑, Lorelei Commin, Marcus Mueller, Volker Piotter, Tobias WeingaertnerKarlsruhe Institute of Technology (KIT), Institute for Applied Materials, P.O. Box 3640, 76021 Karlsruhe, Germanya b s t r a c tTungsten and tungsten alloys are presently considered to be the most promising materials for plasmafacing components for future fusion power plants. The Karlsruhe Institute of Technology (KIT) divertordesign concept for the future DEMO power plant is based on modular He cooled finger units and thedevelopment of suitable mass production methods for such parts was needed.A time and cost effective near net shape forming process with the advantage of shape complexity,material utilization and high final density is Powder Injection Molding (PIM). This process allows alsothe joining of two different materials e.g. tungsten with a doped tungsten alloy, without brazing.The complete technological process of 2 Component powder injection molding for tungsten materialsand its application on producing real DEMO divertor parts, characterization results of the finished partse.g. microstructure, hardness, density and joining zone quality are discussed in this contribution.1. IntroductionPowder Injection Molding (PIM) is a fabrication process in powder metallurgy for shaping metals and ceramics near net shapeswith reasonably tight tolerance and good surface finishes [1 3].This process enables the mass production of low cost, high performance and complex geometries. Materials with high meltingpoints such as tungsten or tungsten alloys could be effectively fabricated with this process.The PIM process for tungsten, developed at Karlsruhe Instituteof Technology (KIT), comprises four stages: kneading or extrusionof suitable feedstocks (combination of powder and binder), injection molding of green parts, debinding and the heat treatment process. The properties of the successfully manufactured divertor parttile, consisting only of pure tungsten, were a high density >98%T.D., a hardness of 457 HV0.1 and a microstructure without cracksor porosity [4]. Additionally, the further development of this process allows the joining of different materials via 2 ComponentPIM. Through the high strength and thermal conductivity, thelow thermal expansion, low tritium inventory and low erosion rate,tungsten is an attractive material to be used in a wide range ofapplications in blanket first walls and divertor Plasma Facing Components (PFC) including plasma facing armor for future fusionpower plants [5]. The development of divertor design conceptsfor the future DEMO power reactor at the KIT comprises the development of materials and fabrication technologies. One promisingbut very complex concept is based on modular He cooled fingerunits. More than 250,000 single parts are needed for this wholedivertor system with aiming for a lifetime of 2 years [6]. The conventional fabrication of such parts by mechanical machining suchas turning and milling is very difficult, time and cost intensive.However 2 Component PIM as a special process allows the suitablemass production of divertor parts and the joining of two differentmaterials without brazing thus saving cost and time.2. Experimental2.1. Used powdersFor the preparation of the binary tungsten powder particlesystems two powders of pure tungsten, with an average grain sizedistribution in the range of 0.7 lm (W1) 1.7 lm (W2) Fisher SubSieve Size (FSSS) were used and mixtures of 50% W1 + 50% W2compounded. For the doped tungsten alloys Lanthanum Oxide(La2O3) powder (FSSS < 2.50 lm) and Yttrium Oxide (Y2O3) powder(FSSS < 1.50 lm) are used.2.2. Powder and feedstock preparationFor the powder preparation a planetary ball mill (Fritsch,Germany) was used and two different powder compositions wereprepared. For the composition of W 2La2O3, the binary tungstenpowder particle system was doped with 2 wt.% La2O3 powderFig. 1. The kneading curve of pure binary tungsten.Fig. 3. The used heat-treatment process.and for W 2Y2O3 with 2 wt.% Y2O3 powder. The details of the powder preparation are reported elsewhere [7].After heating at 80 C for removing moisture the powders aremixed to the so called feedstock with a 50 vol.% wax/thermoplasticbinder system in a kneader (Brabender, Germany) at 120 C. A typical kneading curve for pure binary tungsten is shown in Fig. 1.During the filling period, the torque increases through the additionof powder and binder. After the kneading period, follows the steady period with a homogenous torque the feedstock is ready forfurther processing. The finished granulated feedstock must behomogenous and free from agglomeration.2.3. Producing of 2 Component PIM divertor mockupsTo replicate the divertor mockup a new fully automatic PIM toolwas developed (see Fig. 2). This tool allows the fabrication of thetungsten tile and the tungsten alloy thimble in one step, withoutadditional brazing. The injection molding was carried out on anFERROMATIK MILACRON K50 injection molding machine (FERROMATIK MILACRON, Germany) at a feedstock temperature of160 C and a mold temperature of 50 60 C. After injection molding the so called green parts were debinded: at first, solventdebinding in n Hexane is performed for 48 h at 50 C followed bya thermal debinding step for 1/2 h at 550 C in dry H2 atmosphere.During the debinding step not only the binder and the impuritiesFig. 2. The new fully automatic 2-Component(mainly O and C) are removed, but also the high residual stressesgenerated during injection molding are released. The subsequentheat treatment process (see Fig. 3) consists of pre sintering in asinter furnace (MUT, Germany) at 1800 C in dry H2 for 2 h to reachclosed porosity (which is necessary for the HIP cycle) and compaction is achieved by a suitable HIP cycle (Dieffenbacher, Germany)up to 2100 C under 250 MPa and argon atmosphere for 3 h.Fig. 4 shows the difference of the microstructure (fracture surface)of a pure binary tungsten part after pre sintering and as finishedpart (after pre sintering and HIP). The theoretical density afterpre sintering is >95% T.D. and for the finished part >98% T.D. TheHIP cycle generates parts with high density and low porosity.The finished 2 Component PIM divertor mockups after heat treatment are shown in Fig. 5. The shrinkage of the finished parts afterthe heat treatment process is nearly 20%.2.4. Characterization methodsThe metallographic analyses of the surfaces and the quality ofthe joining zone were examined with a scanning electron microscope (SEM, Zeiss SUPRA™55). Auger electron spectroscopy (AES)with an Auger Nanoprobe PHI 680 (Physical Electronics, USA)was used to characterize the interface between tungsten and thetungsten alloys. The density was measured with a He pyknometricPIM tool to replicate the divertor mockup.Fig. 4. SEM images of the fracture surface: only pre-sintering pure binary W (left) and pre-sintering + HIP pure binary W (right).Fig. 5. Green part with gating system (left) and finished parts after heat-treatment (middle + right).Fig. 6. Analyses of the joining zone quality via SEM and AES for the mockup combination W + W-2La2O3.analyzer and for the Vickers hardness on the polishedsurface of the samples a Shimadzu HMV 2000 hardness testerare used.3. Microstructure and interface characteristics of the finished 2-Component PIM divertor mockupsMetallographic investigations reveal that the material connection of the two component powder injection molding combinations W + W 2La2O3 and W + W 2Y2O3 are successful (see Figs. 6and 7). No cracks or gaps in the seam of the joining zone betweenthe W tile and the W alloy thimble are visible. The Auger electronmeasurements (Figs. 6 and 7, right) show the elemental concentration of tungsten across the interface of the finished parts. In bothfigures, the color of the W matrix is shown in red and the colorof the embedded particles (La2O3 respectively Y2O3) is black. Forboth material combinations a solid bond of the material interfacewas achieved.Fig. 7. Analyses of the joining zone quality via SEM and AES for the mockup combination W + W2Y2O3.Table 1Results of density, hardness and grain size of the finished parts after heat-treatment.Material Theoretical density (% TD) Vickers-hardness (HV0.1) Grain size (lm)W 98.6–99.0 457 5–7W-2La2O3 96.5–97.2 586 >3W-2Y2O3 96.3–97.1 617 <3The resulting microstructure (metallographic section) of thefinished mockups is also shown. The embedded spherical particles(La2O3 respectively Y2O3) in the tungsten matrix are marked bywhite arrows. Pure PIM tungsten parts achieve a density of 98.699% T.D., a Vickers hardness of 457 HV0.1 and a grain size between5 and 7 lm. The grain size for the material composition W 2La2O3is smaller, with an average value of 3 lm and the relative density isover 97% T.D. and the Vickers hardness 586 HV0.1. Once again isthe grain size smaller for W 2Y2O3 with values below 3 lm. Thesecomposition achieves also a density of over 97% T.D. but theVickers hardness is 617 HV0.1 and still higher than forW 2La2O3. Density, hardness and grain size results for the finishedparts after heat treatment are summarized in Table 1. For bothdoped materials the embedded particles act as grain growth inhibitor and generate a small grain size in comparison to pure PIMtungsten. The effect of the grain boundary strengthening is alsoseen in the results of the Vickers hardness. These results are verysignificant for W 2Y2O3.4. Conclusions and outlookThe motivation for this work was the investigation of a suitablemanufacturing method for divertor components consisting of different tungsten materials. Based on the previous results of thetungsten PIM divertor part tile, the experience and the knowledgeof the material development and pretests of basic two componentPIM parts was transferred to produce real divertor components viapowder injection molding. A newly developed fully automatic twocomponent powder injection molding tool allows the replication offusion relevant components such as the tungsten tile and the tungsten alloy thimble in one step without additional brazing. Themicrostructure of the finished samples, and the quality of thejoining zone, were characterized and found to be worthwhile forfurther investigations. This is a promising outcome to further enhance the use of mass production PIM parts for the DEMO fusionreactor.Further steps will be the investigation of material properties bymechanical characterization and via high heat flux tests.AcknowledgementsThis work, supported by the European Communities under thecontract of association between EURATOM, KIT, was carried outwithin the framework of the European Fusion Development Agreement. The views and opinions expressed herein do not necessarilyreflect those of the European Commission.The authors are grateful to all colleagues from the KIT, especially Mr. Heinz Walter and Mr. Sascha Enke for the support andfruitful discussions.References[1] R.M. German, Metal Injection Molding, Metal Powder Industries Fed., PrincetonN.J., 2011. ISBN 978-0-9819496-6-6.[2] T. Müller, V. Piotter, K. Plewa, M. Guttmann, H.-J. Ritzhaupt-Kleissl, J. Hausselt,Microsystem Technologies 16 (8) (2012) 1419–1423.[3] T. Hanemann, R. Heldele, T. Mueller, J. Hausselt, International Journal of AppliedCeramic Technology 8 (4) (2010) 865–872.[4] S. Antusch, P. Norajitra, V. Piotter, H.-J. Ritzhaupt-Kleissl, L. Spatafora, FusionEngineering and Design 86 (2011) 1575–1578.[5] K. Hesch, J. Aktaa, S. Antusch, L.V. Boccaccini, C. Day, D. Demange, W.H. Fietz, G.Gantenbein, A. Möslang, P. Norajitra, M. Rieth, Fusion Science and Technology61 (2012) 64–69.[6] M. Rieth, S.L. Dudarev, S.M. Gonzalez de Vicente, J. Aktaa, T. Ahlgren, S. Antusch,D.E.J. Armstrong, et al., Journal of Nuclear Materials 432 (2013) 482–500.[7] S. Antusch, M. Müller, P. Norajitra, G. Pintsuk, V. Piotter, H.-J. Ritzhaupt-Kleissl,T. Weingärtner, Fusion Science and Technology 62 (2012) 110–115.

Two component tungsten powder injection molding - An effective mass production process

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Two component tungsten powder injection molding - An effective mass production process

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