الفهرس 
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Abstract
Composite materials are attracting considerable interest worldwide
because of their superior mechanical and tribological properties. This study
aims to fabricate and characterize two series of composites; namely (WC-Co-
TaC-NbC) and (WC-Co-5wt. %Ni-TaC-NbC), with addition of Yttrium oxide
to be used as cutting tool materials. The composite materials were fabricated
by powder metallurgy technique (PM) on three stages.
Composites with 0, 2.5, 5, 7.5 and 10wt. % Yttrium Oxide were
fabricated using a mechanical mixing technique. Sintering was carried out in
a vacuum furnace for 1.5 hr at 1450°C. The sintered products have been
characterized by X-ray diffraction (XRD) and scanning electron microscope.
The effects of Yttrium Oxide percentage on the density, microstructure,
hardness, fracture toughness and compression strength have been investigated.
XRD tests have shown that composites with 0, 2.5, 5, 7.5 and 10wt. %
Yttrium Oxide have no new phases formed between Yttrium Oxide and WC.
On the other hand, 𝜂 phase was formed between WC and Co.
Microstructural investigations have shown that the addition of Yttrium
Oxide more than 2.5% increases the grain size of WC and decreases the
relative density. The composite containing 2.5% Yttrium Oxide showed the
highest hardness and compression resistivity. Fracture toughness and
Transverse rupture strength (TRS) increased linearly with the increase of
Yttrium Oxide. For the composites WC-Co-5wt%Ni with Y2O3 content from 0
to 10 wt.%, the XRD showed the formation of 𝜂 phase from the reaction of
WC with Co. Hardness value decreased with increasing Yttrium Oxide
addition due to the increase of porosity. The highest of the TRS and fracture
toughness value was pronounced at 2.5% Yttrium Oxide due to the decrease
of brittle phase content and increasing grain size. The composite containing
7.5% yttrium oxide showed the highest compression resistivity due to
decreasing grain size and increasing phase.