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Processing of WCu graded materials from attritormilled WCuO mixtures is described.
The powder reduction steps are investigated by TG and XRD analyses and by microstructural
observations (SEM, TEM). Sintering of reduced powder with different compositions is analysed by
dilatometry. Sintering behaviour of the graded component processed by cocompaction of a
10/20/30wt%Cu multilayer material is briefly discussed. Liquid Cu migration is observed and
smoothes the composition gradient. Perspectives to control this migration are discussed.
WCu functionally graded materials offer the opportunity to combine a refractory Wrich phase
having a low thermal expansion coefficient and a high strength with a Curich phase having a high
thermal and electrical conductivity. A possible application is first wall assembly samples for the
future nuclear fusion experiment ITER [1]. Smooth transition from Wrich phase to Curich phase
would limit the thermomechanical stresses between W facing plasma and the Curich heat sink. In
case of electrical contacts a graded structure between the contact area and the bulk materials could
also be beneficial. Graded WCu structures can also be used as heat sinks for packaging
microelectronic devices, the composition in the Wrich part being adjusted to match the thermal
expansion coefficient of the semiconductor or ceramic material [2]. However, WCu powder
mixtures usually exhibit a poor sinterability, due to the weak chemical interaction between W and
Cu. Relatively high sintered densities could nevertheless be obtained starting from WCuO powder
mixtures, although the effect of the CuO reduction on sintering is still not clear [3].
WCuO powder mixtures with compositions corresponding to 10, 20 and 30wt% Cu in the reduced
mixture were prepared. CuO Aldrich 241741 powder consists of particles with a broad particle
size distribution (0.7100 ;m) and irregular shape whereas W Eurotunsgtene AW1106 powder has a
rather narrow primary particle size distribution (0.30.5 ;m), with agglomerates up to 100 ;m. A
first set of mixtures was processed through attritor milling for 3h in acetone media with tungsten
carbide balls. Dried powders were uniaxially compacted into cylindrical samples (=8 mm ; =68
mm) under 400 MPa. The powder reduction steps were characterized by thermogravimetric
analyses (TGA), dilatometry, XRD, SEM and TEM microstructural analyses. A second set of
mixtures was processed to improve the sintering ability. The milling conditions were first optimized
and powders were reduced at 350°C for 2h and granulated with 1wt% polyethylene glycol (PEG)
before uniaxial compaction. Green compacts were sintered at temperatures up to 1300°C under
He/H
2
reducing atmosphere (4vol% H
2
). Graded samples were processed by cocompacting and co
sintering stack of powder layers with different compositions.
Materials Science Forum Vols. 534-536 (2007) pp 1569-1572
Online available since 2007/Jan/15 at www.scientific.net
© (2007) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/MSF.534-536.1569
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,
www.ttp.net. (ID: 129.128.216.34, University of Alberta, Edmonton, Canada-08/10/14,15:32:26)