Estudo da substituição parcial do ligante Co pelo Nb no metal duro preparado via MAE e sinterizado em forno convencional, alto vácuo e por pulso de plasma
Hard metal, also known as cemented carbide, is a widely used material in various applications such as turning, milling, and drilling. The most commonly used hard metal consists of a major hard phase of WC (tungsten carbide) and a minor metallic binder phase of Co (cobalt), usually making up less...
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| Format: | doctoralThesis |
| Sprache: | pt_BR |
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Universidade Federal do Rio Grande do Norte
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| Online Zugang: | https://repositorio.ufrn.br/handle/123456789/56508 |
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| Zusammenfassung: | Hard metal, also known as cemented carbide, is a widely used material in various
applications such as turning, milling, and drilling. The most commonly used hard
metal consists of a major hard phase of WC (tungsten carbide) and a minor metallic
binder phase of Co (cobalt), usually making up less than 25% by mass. However,
although the use of Co as a binder results in improved mechanical properties for the
cemented carbide, the scientific community has been seeking a partial or complete
substitute for this binder due to its toxicity and scarcity. In light of this, this research
aimed to evaluate the possibility of partially replacing Co with Nb (niobium). For this
purpose, composite powders of WC-10%Co, WC-2.5%Nb-7.5%Co, and WC-5%Nb5%Co were prepared using wet high-energy milling (HEM) for 2, 15, and 30 hours.
The milled powders were compacted at 250 MPa and subsequently sintered in a
conventional resistive furnace at 1450°C and 1550°C. The powders processed via 30-
hour WHEM were also sintered using two distinct routes to achieve better properties
for the hard metal. In the first route, the milled powders were compacted at 250 MPa
and sintered in high vacuum (10-4
torr) at a temperature of 1550°C. In the second route,
the powders were sintered using spark plasma sintering (SPS) at a temperature of
1300°C. The starting powders, milled powders, and sintered samples were
characterized using field emission scanning electron microscopy (FESEM), X-ray
diffraction (XRD), and energy-dispersive spectroscopy (EDS). Particle size
distribution measurements were also conducted for the powders. The density of the
sintered samples was determined using the Archimedes' method. Additionally,
Vickers microhardness measurements were carried out on the sintered samples. The
results revealed that the HEM process efficiently promotes phase homogenization and
particle size reduction, facilitating the sintering process of the composite powders.
The SPS technique for the 30-hour milled powders proved to be more effective in
enabling the partial substitution of Co with Nb, resulting in a relative density of
84.23% for the cemented carbide WC-5%Co-5%Nb with high microhardness and
without the formation of the η phase. |
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