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ve 1 Microstructural Characterization of Cu-W Functionally Graded Materials
Dragana Jankovic Ilic, Lisette Granberg , Frank Miicklich
Saarland University, Department of Materials Science, Functional Materials, Germany
Abstract
High-thermal conductivity of copper and low-thermal expansion coefficient of tungsten makes Cu-
W functionally graded materials (FGM) attractive candidates for the application in fusion reactors
as heat sink , as laser beam targets or as diamond tools.
Three and six-layer Cu-W samples have been manufactured from W and Cu powders by hot
pressing. Due to the difference in the sintering behaviour, the consolidation had to be adopted to the
amount of Cu and W in each individual layer.
Electron beam tests on the 3 and the 6 layer compositions of Cu-W FGM have been performed to
investigate the effect of thermal shock induced surface modification. Due to formation of a liquid
phase in W layer the most critical erosion mechanism is associated with instabilities in the molten
pre layer.
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1.Introduction
Functionally graded materials have properties which continuously change through the
material. This property gradient is usually caused by a gradient in chemical composition or
microstructure. Due to its potential for high-thermal conductivity and low-thermal expansion
coefficient, Cu-W FGMs show an excellent resistance to electric discharges and are therefore used
as contact materials in high power switches [1]. Because of the large reduction ability of thermal
stresses in interface region, Cu-W FGM are expected as system components used in the high
temperature range (gas turbine, heat sink in fusion reactor, laser beam target, etc). Particularly, the
beam target (where the front surface is heated by high temperature heat source and the back surface
is cooled by water), is required to have both the heat resistance properties at the heating side and the
good thermal conductivity for the enhancement of cooling property [2]. In the International
ns Thermonuclear Experimental Reactor (ITER) parts of the baffle, as well as the upper regions of the
inner and outer vertical targets of the divertor will be armored with W [3]. In such condition the
Cu-W bond is exposed to repeated thermal shock leading to accumulation of plastic strains and
fracture at the bonded interface.
ww N gr The first graded tungsten-copper composites have been manufactured by Takahashi et.al
A erkennbar, [4]. They have produced tungsten performs with graded porosity by stacking, sintering and capsule-
entstanden sind. free hot isostatic pressing. The most widely used production method is preparing a sintered skeleton
with the desired density, and than infiltration with Cu [1,3]. It has been shown that addition of a
small amount of Fe, Co, Ni can help in wetting copper and tungsten surfaces and improving the
au. Bei dessen infiltration efficiency [5]. Centrifugal Powder Forming is a method which offers the possibility for
ı Materials als the development of gradient with different concentration limits, different exponents of gradient
function, and for pore structure gradient [6]. Electrochemical processing is novel production route
based on the position dependent electrochemical reaction of porous performs [7].
Differences in thermal expansion between these two metals (CTEw=4,6 ppm/°C, CTEcu=16,6
ing ppm/°C), makes it difficult to produce the material with high density. Different thermal and
{heir mechanical properties also produce high residual stresses , which tend to develop close to the
72 (199) interface. As a consequence delamination, spallation and crack propagation occur.
; The aim of the present work is to investigate microstructural changes in Cu-W FGM
material caused by plasma disruption. Special attention was focused on influence of different
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