Microstructural influence on tolerance to corrosion-induced damage in hardmetals

Abstract

The influence of the microstructure on the tolerance of WC-Co cemented carbides to corrosion damage was studied by using residual strength as the critical design parameter. In doing so, samples were immersed in synthetic mine water solution for different times, and changes induced by corrosion exposure were assessed. A detailed 3D FIB/FESEM tomography characterization of corrosion damage-microstructure interactions is included. Results reveal that corrosion damage may result in relevant strength degradation on the basis of stress rising effects associated with the formation of surface corrosion pits. Thus, as immersion time increases strength gradually decreases. Fractographic examination reveals the formation of semi-elliptical and sharp corrosion pits for studied medium-and ultrafine-sized cemented carbides, respectively. The latter has a much more pronounced stress rising effect, and consequently higher strength losses were determined for ultrafine grades. Corrosion process consists of a selective attack of the binder that is dissolved in the corrosive media. Initially, it is located at centres of binder pools and as exposure time in the media increases, corrosion evolves consuming the rest of the pools which finally leaves an unsupported WC grain skeleton at the surface.

Corrosion-Induced Damage and Residual Strength of WC-Co,Ni Cemented Carbides: Influence of Microstructure and Corrosion Medium

“…Several studies have shown detrimental corrosion effects on the effective wear resistance of cemented carbides, as a result of synergic interactions among different degradation phenomena [13][14][15]. Similar correlations have been reported regarding residual strength, measured under either monotonic or cyclic loads [16][17][18][19][20][21]. However, most of these works have focused on either one particular hardmetal grade or a specific corrosive medium.…”

“…Table 1. Microstructural parameters, hardness and fracture toughness for the investigated cemented carbides [20,23,24]. Corrosion behavior was studied on the basis of the electrochemical response of the studied grades in three different solutions: acidic (0.1M HCl), neutral containing chlorides (0.1M NaCl), and alkaline (0.1M NaOH).…”

“…As reported in previous investigations, sharp corrosion pits are formed in ultrafine-sized cemented carbides as immersion time increases, which have a much more pronounced stress rising effect. Consequently, higher strength loss was expected for ultrafine grades [19,20].…”

Strength and reliability of WC-Co cemented carbides: Understanding microstructural effects on the basis of R-curve behavior and fractography

“…On the other hand, their extremely high Weibull modulus is principally related to their high toughness level, which imparts extremely high damage tolerance levels [22,42,43].…”

Focused ion beam tomography of WC-Co cemented carbides

“…In addition, possible defects in the material, either intrinsic to processing or induced under service (e.g. stable grown cracks [27,28] or corrosion pits [29,30]) will also be 3D in nature and will then interact with the microstructure in a non-planar way too.…”