Physical and mechanical properties of bilayer cemented tungsten carbide and steel fabricated through die compaction process
In this study, a bimaterial of cemented tungsten carbide (WC) and steel was fabricated via die compaction process as it combines the hardness of WC and toughness of steel used for making machine tools. Major challenges related to this study is in two folds; firstly, the cobalt (Co) commonly used...
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| Format: | Thesis |
| Language: | English |
| Published: |
2016
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/67080/1/FK%202016%20150%20IR.pdf |
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| Summary: | In this study, a bimaterial of cemented tungsten carbide (WC) and steel was fabricated
via die compaction process as it combines the hardness of WC and toughness of steel
used for making machine tools. Major challenges related to this study is in two folds;
firstly, the cobalt (Co) commonly used as WC binder has been reported to be scarce in
supply and toxic making the International Agency for Research on Cancer (IARC)
classify sintered WC–Co hard metals as carcinogenic and harmful to humans.
Secondly, microstructural analysis has revealed the formation of detrimental phase (eta
carbide) in co-sintered tungsten carbide and steel bilayer resulting in the deterioration
of properties of this bilayer. Therefore, there is a need to replace cobalt with iron (Fe)
as the binder, and also control the carbon (C) content in Fe as part of the composition
in order to suppress eta carbide formation. WC–Fe–C and Fe–W–C bimaterial was
fabricated with varying carbon content of Fe part composition (Fe–6W–xC, x = 0.2,
0.4, 0.6 and 0.8 wt.%). Sintering temperature was varied (1280oC, 1290oC &1295oC)
to control the sintering kinetics and limit mismatch between layers that commonly
occur in bilayer compacts. Microstructural analysis revealed significant reduction of
the eta carbide phase with increasing carbon content as the bilayer specimen, MC–0.8
with the highest carbon addition (0.8 wt.%) sintered at 1280oC was observed to have
vestigial trace of eta carbide phase when compared to other samples. An improved
density results (6.1%) with increased carbon level resulting in stronger interfacial bond
was observed in bilayer samples sintered at 1280oC, while weak interfacial bond owing
to shrinkage mismatch was observed in samples sintered at 1295oC. Hardness values
increased with increasing carbon addition at all sintering temperatures (At 1280oC,
MC–0.2 = 132.80 & 692.93 kgfmm-2 while MC–0.8 = 150.97 & 735.70 kgfmm-2 for
Fe and WC parts respectively) which was attributed to the reduction of eta carbide
formation. Through diametral compression test, bilayer samples sintered at 1280oC
were found to possess higher values of tensile strength which significantly increased
from 45.10 MPa to 55.75 MPa with increase in carbon content. |
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