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

Corrosion-induced changes on Hertzian contact damage in cemented carbides

“…Concerning the specimens previously exposed to acidic media and then tested, Figure 10 clearly points out the lessening effects J o u r n a l P r e -p r o o f of corrosion on the resistance to nucleation and development of contact damage. This is quite clear in terms of both lower critical loads for the emergence of incipient cracks, and more severe damage evolution scenarios, in agreement with works published recently [31,32]. Regarding the former, it can be directly attributed to binder removal and the consequent loss of the main (intrinsic)…”

“…Indentation stress-strain response seems to significantly depend on the depth of the corrosion affected zone. From a physical viewpoint, the degraded load-bearing capability evidenced must be attributed to the generation of porous/binderless corroded layers after corrosive exposure [28][29][30][31], as shown in Figure 5. In this regard, based on recent findings reported by the authors for sharp indentation and scratch testing of corroded hardmetals [31], the degraded layer is not expected to play a significant role in the plastic yielding onset until its thickness reaches a certain value.…”

“…From a physical viewpoint, the degraded load-bearing capability evidenced must be attributed to the generation of porous/binderless corroded layers after corrosive exposure [28][29][30][31], as shown in Figure 5. In this regard, based on recent findings reported by the authors for sharp indentation and scratch testing of corroded hardmetals [31], the degraded layer is not expected to play a significant role in the plastic yielding onset until its thickness reaches a certain value. Within this context, considering the overlapping of indentation stress-strain curves in Figures 7b and 7c, it may be stated that corroded layers resulting from exposure to 72 hours for 6NiCrM and 6CoCrM grades are thin enough, such that whole quasi-plastic deformation is still controlled by the uncorroded substrate.…”

“…On one hand, leached binder J o u r n a l P r e -p r o o f leaves effective pores which may act as stress concentrators and crack precursors within binderless WC skeleton. On the other one, lack of binder implies that toughening mechanisms associated with ductile ligament reinforcement are now completely absent; and thus, energy required for subcritical crack propagation is effectively much lower than for the pristine condition [30][31][32]. Hence, induced microcracks may lead to catastrophic failure of the specimen as they propagate, interact and finally coalesce to form long cracks [31][32][33]50,52,69,70].…”

“…A quite interesting outcome from these studies is the detailed understanding acquired on the damage mechanisms at the micro-and nanometric dimensions: cracking, fragmentation and easy removal of WC grains under (sliding) contact, directly associated with the mechanically unsupported, contiguous and binderless/porous carbide network left after J o u r n a l P r e -p r o o f exposure to corrosive media of the studied hardmetals. However, similar information linking corrosion-induced damage and contact mechanical response at relatively higher length scales is quite limited [31,32]. To fill this lack of knowledge, the present study aims to evaluate the influence of corrosion-induced changes on the contact damage response of cemented carbides, by implementing spherical indentation tests.…”