Resumo:
Cemented carbide is a composite material consisting of hard ceramic particles
embedded in a ductile metal matrix, called the binder phase. These materials exhibit a
unique combination of mechanical properties, having several engineering applications.
Currently, cobalt is the binder that dominates the cemented carbide market due to better
mechanical properties. However, due to the high cost, scarcity and the search for
cemented carbides with greater corrosion resistance, an alternative binder phase has
been researched. Nickel is an exciting and promising candidate but, the mechanical
properties of WC-Ni cemented carbides are relatively inferior to those of WC-Co
cemented carbides. Thus the addition of alloying elements, such as molybdenum and
chromium, has been studied in order to promote the strengthening of the WC-Ni alloys
by using solid solution techniques. The aim of this work is to evaluate the corrosion
resistance of WC-NiMo, WC-NiCr and WC-Co cemented carbides, obtained by
conventional powder metallurgy. The sintered sample was characterized, , before and
after corrosive tests, by the analysis in optical microscopy (OM), scanning electron
microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS), X-ray diffraction
(XRD. Microhardness was measured by the Vickers microhardness method. The
corrosion resistance of the cemented carbides was investigated by open circuit potential,
potentiodynamic polarization, electrochemical impedance spectroscopy and static
immersing corrosion test, in a 3.5 wt.% NaCl solution. The WC-Ni cemented carbides
showed microstructures similar to those of conventional cemented carbides, WC-Co.
However, pores and binder islands were observed in the microstructures, which leads to
inferior mechanical properties, such as Vickers microhardness. The corrosion tests had
promising results, the WC-NiMo e WC-NiCr cemented carbide showed superior
corrosion resistance and higher passivation capacity than the WC-Co cemented carbide.
The WC-NiMo cemented carbide was the material with the best performance, as it
maintained good mechanical properties and presented the noblest corrosive behavior
among the studied materials.
