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Abstract
For rock drilling applications, the cemented carbides containing hard WC grains in a ductile Co binder are commonly used as drill buttons. In considering the environmental and health aspects an alternate to Co-binder is pursued. In the present work, using standard scratch testing the friction and wear properties of the WC-20 vol% Ni grade is studied and compared to that of WC-20 vol% Co grade. The deformation and wear characteristics of the cemented carbide grades are evaluated and correlated to the microstructural changes during scratch testing. Also, the electrochemical impedance spectroscopy (EIS) behavior of the as-polished and scratch-tested cemented carbides was studied at the open circuit potential condition of simulated mine water (SMW) for 1 h. The obtained polarization resistance and charge transfer resistance values from the EIS analysis are correlated to the corrosion resistance of the samples. In both as-polished and scratch-tested conditions the WC-Ni grade exhibited higher polarization resistance values indicating high corrosion resistance than the WC-Co. In comparison to the as-polished sample, both the scratch-tested cemented carbides exhibited higher corrosion activity in particular within the scratch-induced tribo-layer. Severe corrosion and complete removal of the tribo-layer was observed for the WC-Co grade when exposed to SMW for 15 h. Site-specific scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX) analysis were carried out to get insight into the corrosion behavior of as-polished and scratch-tested cemented carbides.
Highlights
Cemented carbides are produced through the powder metallurgy route by consolidating a hard refractory phase of tungsten carbide (WC) with a soft metal (Co) binder phase and depending on the application, the microstructure, properties of these composites shall be tailored [1]
This study has emphasized the effect of the modified composition and microstructure of the tribo-layer in the scratched area that has resulted in a higher corrosion activity for both the cemented carbide grades
With the aim to increase the understanding of the combined effects of mechanical and corrosion degradation of two different cemented carbide grades, scratch testing followed by corrosion testing and detailed posttest surface characterization using scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX) have been performed
Summary
Cemented carbides are produced through the powder metallurgy route by consolidating a hard refractory phase of tungsten carbide (WC) with a soft metal (Co) binder phase and depending on the application, the microstructure, properties of these composites shall be tailored [1]. Apart from several applications in many industries, WC-Co cemented carbide is been used as tool inserts in geo-engineering projects, due to its high hardness, strength, toughness, and high wear resistance [2]. The failure of the WC-Co drill buttons or drill inserts is the key limitation during the geo-engineering applications such as rock drilling, mineral cutting, and oil-gas drilling, and tunneling. To improve the mechanical and corrosion properties of the cemented carbides, researchers have consid ered replacing the Co binders with simple Fe or Ni metal [8,9]. To verify the wear and corrosion resistance of the newer grade cemented carbides in the field testing conditions of a rock drilling application could be often complicated and expensive. To characterize the corrosion properties of cemented carbides, electrochemical experiments were conducted in various corrosive environments, including H2SO4 [11,15,16,17], HCl [10], NaCl [12,18], NaOH [10], Na2SO4 [12], simulated
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