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Tungsten-Based Nanocomposites by Chemical Methods Tungsten-Based Nanocomposites by Chemical Methods Sverker Wahlberg Doctoral Thesis in Materials Chemistry Stockholm 2014 KTH Royal Institute of Technology SE-100 44 Stockholm, Sweden TRITA-ICT/MAP AVH Report 2014:20 KTH School of Information and ISSN 1653-7610 Communication Technology ISRN KTH/ICT-MAP/AVH-2014:20-SE SE-164 40, Kista, Sweden ISBN 978-91-7595-368-7 Akademisk avhandling som med tillstånd av KTH i Stockholm framlägges till offentlig granskning för avläggande av teknisk doktorsexamen torsdagen den 11 december kl 10.00 i sal 205, Electrum, KTH, Isafjordsgatan 22, Kista. © Sverker Wahlberg, 2014 Universitetsservice US-AB, Stockholm 2014 2 Abstract Tungsten based-materials find use in many different fields of engineering, particularly in applications where good temperature and/or erosion resistance is important. Nanostructuring of tungsten composites is expected to dramatically improve the materials’ properties and enhancing the performance in present applications but also enabling totally new possibilities. Nanostructured WC-Co materials have been the focus of researchers and engineers for over two decades. New fabrication methods have been developed. But, the fabrication of true nanograined WC-Co composites is still a challenge. Nanostructured tungsten-based materials for applications as plasma facing materials in fusion reactors have attracted a growing interest. This Thesis summarizes work on the development of chemical methods for the fabrication of two different types of nanostructured tungsten-based materials; WC-Co composites mainly for cutting tools applications and W-ODS materials with yttria particles, intended as plasma facing materials in fusion reactors. The approach has been to prepare powders in two steps: a) synthesis of uniform powder precursors containing ions of tungsten and cobalt or yttrium by precipitation from aqueous solutions and b) processing of the precursors into WC- or W-based nano-composite powders. Highly homogenous W- and Co- containing precursors for WC-Co composites were prepared via two different routes. Keggin-based precursors ((NH4)8[H2Co2W11O40]) were made from sodium tungstate or ammonium metatungstate and cobalt acetate. The powder composition corresponded to 5.2 % Co in the final WC-Co material. In a second approach, paratungstate- based precursors (Cox(NH4)10-2x[H2W12O42]) were prepared from ammonium paratungstate (APT) and cobalt hydroxide with different compositions corresponding to 3.7 to 9.7 % Co in WC-Co. Both precursors were processed and sintered into uniform microstructures with fine scale (<1μm). The processing of paratungstate-based precursors was also further investigated. WC-Co powders with grains size of less than 50 nm were obtained by decreasing processing temperatures and by applying gas phase carburization. W-ODS materials were fabricated starting from ammonium paratungstate and yttrium salts. Paratungstate-based precursors were prepared with different homogeneities and particle sizes. The degree of the chemical uniformity varied with the particle size from ca 1 to 30 μm. Tungsten trioxide hydrate-based precursors made from APT and yttrium salts under acidic conditions had higher uniformity and smaller particle size. The tungsten oxide crystallite size was decreased to a few nanometers. Yttrium was included either by doping or in a nanocomposite structure as yttrium oxalate. The nanocomposite precursor was found to be more reactive during hydrogen reduction, facilitating its conversion to pure W-Y2O3 nanopowder. The doped precursor were further processed to nanopowders and sintered to highly uniform W-1.2%Y2O3 composites. In summary, APT was converted to highly homogenous or uniform powder precursors of different compositions. The transformations were carried out in aqueous suspensions as a water- mediated process. These precursors were processed further in to nano-sized powders and sintered to highly uniform tungsten composites with fine microstructures. 3 Thesis Content This doctoral thesis summarizes work on chemical methods for the fabrication of WC-Co and W-Y2O3 composites. Parts of the text have been published earlier by the author in the licentiate thesis “Nanostructured Tungsten Materials by Chemical Methods” presented at KTH in Kista, Stockholm, 2011. Papers included in the Thesis I. S. Wahlberg, I. Grenthe and M. Muhammed, Nanostructured hard material composites by molecular engineering. 1. Synthesis from soluble tungstate salts, Nanostruct. Mater., 1997, 9, 105 II. Z. Zhang, S. Wahlberg, M. Wang and M. Muhammed, Processing of nanostructured WC-Co powder from precursor obtained by co-precipitation, Nanostruct. Mater., 1999, 12, 163 III. S. Wahlberg, M. A. Yar and M. Muhammed, Oxide dispersed tungsten powders from yttrium-doped ammonium paratungstates IV. M.A. Yar, S. Wahlberg, H. Bergqvist, H. G. Salem, M. Johnsson, M. Muhammed, Spark plasma sintering of tungsten-yttrium oxide composites from chemically synthesized nanopowders and microstructural characterization, J. Nucl. Mater., 2011, 412, 227 V. S. Wahlberg, M. A. Yar, M. O. Abuelnaga, H.G. Salem, M. Johnsson and M. Muhammed, Fabrication of nanostructured W-Y2O3 materials by chemical methods, J. Mater. Chem., 2012, 22, 12622 VI. M.A. Yar, S. Wahlberg, M.O. Abuelnaga, M. Johnsson, M. Muhammed, Processing and sintering of yttrium-doped tungsten oxide nanopowders to tungsten-based composites, J. Mater. Sci., 2014, 49, 5703 VII. S. Wahlberg, M.A. Yar and M. Muhammed, Solution chemical synthesis of W – Y2O3 nanocomposites Contributions of the author Paper I. Part in generation of ideas, performing all synthesis of precursors, writing the article Paper II Part in generation of ideas, performing all synthesis of precursors and part of processing, writing part of the article Paper III Generating ideas, performing all experimental work apart from SEM, writing the article. Paper IV Generating ideas on materials fabrication, preparing precursors, writing part of the article Paper V Generating ideas, performing powder fabrication and characterizations apart from SEM and TEM, writing parts of the article 4 Paper VI Generating ideas, writing part of the article. Paper VII Generating ideas, performing powder fabrication and characterizations apart from SEM, writing the article Patents related to the thesis M. Muhammed, S. Wahlberg and I. Grenthe, Method of preparing powders for hard materials, Swedish Patent SE9402081, 1995 I. Grenthe, M. Muhammed and S. Wahlberg, Method of preparing powders for hard materials from cobalt salts and soluble tungstate salts, Swedish Patent SE9403954, 1996 S. Wahlberg, M. Muhammed and I. Grenthe, Method of preparing powders for hard materials from APT and soluble cobalt salts, Swedish Patent SE9402548, 1996 M. Muhammed, I. Grenthe and S. Wahlberg, Method of preparing multicarbide powders for hard materials, Swedish Patent SE9402555, 1996 Other related publications not included in the thesis M. A. Yar, S. Wahlberg, H. Bergqvist, H. G. Salem, M. Johnsson and M. Muhammed, Chemically produced nanostructured ODS-lanthanum oxide-tungsten composites sintered by spark plasma, J. Nucl. Mater., 2011, 408, 129 5 Abbreviations and symbols ODS oxide dispersion strengthened SPD severe plastic deformation APT ammonium paratungstate AMT ammonium metatungstate TBO tungsten blue oxide CVT chemical vapor transport MM mechanical milling MA mechanical alloying HIP hot isostatic pressing TTH tungsten trioxide hydrate SPS spark plasma sintering ICP inductively coupled plasma XRD X-ray diffraction SEM scanning electron microscope EDX energy-dispersive X-ray spectroscopy TEM transmission electron microscope TGA thermal gravimetric analysis FTIR Fourier transform infrared spectroscopy EGA evolved gas analysis Hv50 hardness K1c fracture toughness CoAPT cobalt ammonium paratungstate mM mmole/L YAPT yttrium ammonium paratungstate WO3_HCl TTH powder synthesized from APT and HCl WO3_HNO3 TTH powder synthesized from APT and HNO3 WO3_YNO3 TTH powder doped with yttrium WO3_YOx composite powder of TTH and yttrium oxalate TG thermogravimetry DTG derivative thermogravimetry BSE back-scattered electrons 6 Contents Abstract .......................................................................................................................................................... 3 Thesis Content .............................................................................................................................................. 4 Papers included in the Thesis ..................................................................................................................... 4 Contributions of the author ........................................................................................................................ 4 Patents related to the thesis ........................................................................................................................ 5 Other related publications not included in the thesis ............................................................................. 5 Abbreviations and symbols ......................................................................................................................... 6 1 Introduction ......................................................................................................................................... 9 1.1 Tungsten Materials – Properties and Applications ................................................................. 9 1.2 Nanostructured Cemented Carbides .....................................................................................
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