Abstract:
This dissertation reports systematic work aimed at determining the plastic
deformation mechanisms that led to strains at fracture as high as 4.7% in WC-Co
alloys at 1000°C when subjected to 3-point bending tests. The three grades
investigated have a Co content of 15wt% and WC grain sizes of 1.3, 0.35 and
0.3
μ
m respectively and were received after they were tested in bending.
Fractography, macrostructural and microstructural investigations were carried out
in attempts to identify the mechanisms leading to the large strains. Techniques
used included light microscopy, scanning electron microscopy (SEM), field
emission scanning electron microscopy (FESEM), energy dispersive spectroscopy
(EDS) and quantitative image analysis.
Through comparisons of the results from the three grades at various temperatures,
it was possible to establish that the large strain at 1000°C are mainly due to
cracking and cobalt drift. During the fractographic investigations it was found that
the grades which contained VC as a grain refiner exhibited steps on the WC grains
and that fracture propagated preferentially along the stepped WC grain
boundaries.
