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

Abstract

The corrosion behavior of cemented carbides with binders of different chemical nature (Co and Ni) and carbides with distinct mean grain size (ultrafine and coarse) was studied. The investigation also included corrosion media (acidic and neutral solutions containing chlorides and an alkaline solution) as experimental variables. Immersion tests were performed to induce corrosion damage in a controlled way. Electrochemical parameters were measured together with a detailed inspection of the corroded surfaces. Microstructural influence on the tolerance to corrosion damage was evaluated in terms of residual strength. Results pointed out that corrosion rates were lower in the alkaline solution. In contrast, acidic media led to higher corrosion rates, especially for cemented carbides with Co regardless the influence of carbide mean grain size. Corrosion damage resulted in strength degradation due to the formation of surface corrosion pits in acidic solution. In neutral and alkaline solutions, much less pronounced effects were determined. Focused Ion Beam (FIB)/ Field Emission Scanning Electron Microscopy (FESEM) results revealed differences in corrosion-induced damage scenario. In acidic solution, corrosion starts at binder pool centers and evolves towards binder/WC interfaces. Meanwhile, corrosion in alkaline solution is initially located at binder/WC interfaces, and subsequently expands into the ceramic particles, developing a microcrack network inside this phase.

Corrosion-induced changes on Hertzian contact damage in cemented carbides

“…The corrosion rate of the latter (≈ 1.7 μm/h) is about four times higher than those exhibited by the other two cemented carbides (≈ 0.4 μm/h). Such a finding is in complete agreement with previous works by different research groups [11,13,14,16,17,21,23,32,51]. On the other hand, replacing most of the Co with Ni within the binder does not seem to improve corrosion resistance.…”

Indentation and scratch testing of a WC-6%wtCo cemented carbide: Corrosion effects on load-bearing capability and induced damage

“…In general, these experimental results highlight the lessening effect of corrosion on load-bearing capability of the hardmetal, as well as the dependence of the measured mechanical response on the ratio between indentation and/or scratch depth (and associated plastic zone) and thickness of the corroded layer, as it will be discussed below. After being exposed to the 0.1M HCl solution, the microstructure assemblage of the corroded zone becomes loose and porous due to the dissolution of the metallic phase [18,19,21]. Thus, the corrosion affected zone may be effectively described as a porous film adhered to a substrate consisting of the non-corroded hardmetal (Figure 1).…”

“…Regarding the former, it is well-known that the original microstructural scenario is changed, through dissolution of different individual phases depending on acidic or basic nature of the media [9][10][11][12][13][14]. Concerning the latter, it is established that rupture, wear and fatigue resistance of corroded hardmetals decrease [5,10,[15][16][17][18][19][20][21]. One reason behind it is the pronounced stress rising effect of corrosion pits.…”

Effect of WC particle size on the microstructure and mechanical properties of Ni–Co coarse grain cemented carbide

“…It is obvious from Table 4 that the variation law of the self-corrosion current density of the alloy is 2# < 3# < 4# < 1# and the 2# specimen has the best corrosion resistance. The study shows that the corrosion rate of cemented carbide in NaCl solution is independent of the average grain size of WC, [26][27] and the corrosion resistance is related to the alloy element content, mean free path, and coherence. And from Table 2, it can be seen that the content of alloying elements in 1#−4# alloy is consistent, so the improvement of corrosion resistance of the alloy mainly depends on the reduction of the mean free path and the improvement of the coherence.…”

“…It has been pointed out that the corrosion mechanism of cemented carbide in NaCl solution is diffusion corrosion from the core of the bonded phase to the surrounding area. 27 The decrease in the mean free path reduces the contact area between WC grains and the bonded phase on the surface of the specimen, which decreases the corrosion rate of the bonded phase per unit of time. And the increase in the coherency can cut the connection between the surface layer and the internal bonding phase, which increases the residual amount of the bonding phase inside the alloy.…”