The development of a diamond-silicon carbide composite
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Date
2009-05-08T11:27:55Z
Authors
Mlungwane, Kekeletso
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Abstract
Two routes of diamond-SiC composite manufacture under ambient pressure were
followed, reaction-sintering and infiltration route. The reaction-sintered product is highly
porous and has a low hardness value of 11 GPa. The infiltrated product on the other hand
is fully dense, exhibits high hardness (> 35 GPa) and shows good wear properties under a
cutting speed of 100 m/min.
Medium to coarse-grained diamond preforms (D[v, 0.9] of 16 to 22 μm) have been
successfully infiltrated using molten silicon. The infiltration of fine-grained diamond
preforms (D[v, 0.9] = 2 μm) using molten silicon is limited by the blocking of the pores
as a result of the volume increase during the reaction of diamond with Si to form SiC.
The preforms were prepared using phenolic resin as a binder. With increasing resin
content the pore size increases, and the infiltration depth increases up to 10 wt% resin
content. Full infiltration has been achieved at 5 and 10 wt% resin in the coarse and
medium-grained preforms respectively. For the fine-grained diamond preforms, a
maximum infiltration depth of 2.5mm was obtained using 10 wt% resin content.
Reaction-choking is the predominant inhibitor to realization of full infiltration.
The investigation of the wetting behavior and the reaction to form SiC revealed that
diamond is well wetted by molten silicon reaching a contact angle of about 20o after its
melting. The rate of SiC formation is initially very fast and slows down with time once a
continuous product layer has formed.