Materials for engineering, 3rd Edition - (Malestrom)

Composite materials 197
So
E
E
c
1
=
2/3
E1 + ( E2 – E1)
f
2/3 1/3
E + ( E – E ) f (1 – f )
1 2 1
[6.2]
Application to tungsten carbide/cobalt cutting tools
These so-called cemented carbide materials are used for high-speed metal
cutting tools and mining drills. The microstructure consists of tungsten
carbide (WC) particles in a matrix of cobalt (Co). The WC is a hard and
brittle phase, and Co is a ductile metal which is able to wet the carbide and
form a strong adhesive bond with it. The alloy is fabricated powder
metallurgically: a fine powder of mixed WC and Co being compacted and
sintered at high temperature.
The Young’s modulus of cobalt is 206.9 GPa and that of tungsten carbide
is 703.4 GPa. If a series of composites of differing volume fractions of
cuboidal WC particles is prepared and their Young’s moduli determined, the
results shown in Fig. 6.6 are obtained. The continuous line in Fig. 6.6 represents
the theoretical composite moduli according to equation [6.2]. It is evident
that the equation well describes the stiffness of the composite.
Application to polymers
The use of appropriate fillers of high modulus in polymers may give, in
600
E (GPa)
400
200
0 0.2 0.4 0.6 0.8 1.0
Fractional volume of cobalt, f
6.6 Young’s moduli of WC–Co composites of differing volume
fraction WC; the continuous line corresponds to equation [6.2].