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

Abstract

Strength and reliability of WC-Co cemented carbides (hardmetals) are dependent on effective fracture toughness as well as on nature, size and distribution of processing flaws. Regarding toughness, they exhibit a crack growth resistance (R-curve) behavior, derived from the development of a multiligament bridging zone at the crack wake. Accordingly, successful implementation of fracture mechanics requires consideration of tangency criterion, between applied stress intensity factor and R-curve, in addition to fractographic inspection. It is the aim of this study to evaluate the strength behavior of a series of experimental WC-Co grades on the basis of R-curve failure criteria. Results indicate that microstructural effects on the strength of hardmetals may be satisfactorily rationalized following the referred criterion.The analysis includes consideration of nature and distribution of fracture origins, found to be more diverse and wider respectively for the harder fine-grained grades. This experimental evidence, together with the fact that these hardmetals exhibit steeper rising R-curves than tougher coarse-grained ones, leads to lower reliability for the former. This investigation documents and validates the great relevance of R-curve behavior for optimizing the mechanical performance of WC-Co cemented carbides on the basis of microstructural design.

Effect of substrate pre‐treatment on the low cycle fatigue performance of tungsten carbide‐cobalt coated additive manufactured 316 L substrates

“…As obtained from Vickers indentation tests, the tungsten carbide‐cobalt coatings sprayed onto the differently pre‐treated 316 L substrates show a fracture toughness K IC of approximately 2.5 MPa √m±0.4 MPa √m. With regard to these results, it is obvious that the fracture toughness K IC is remarkable low compared with either those observed for high velocity oxy‐fuel (HVOF) sprayed tungsten carbide‐cobalt coatings or tungsten carbide‐cobalt cemented carbides [20, 21]. The degree of decarburization in high velocity oxy‐fuel (HVOF)‐sprayed tungsten carbide‐cobalt coatings has a decisive influence on the fracture toughness K IC [22].…”

A Review on Fatigue Mechanisms and Approaches for Hard metals

“…The performance of these metal binder phase depends on usage, performance criterion was to determine and analyseimpactful of fatigue strength leading to rupture and Fatigue crack growth (FCG) [10], [14].Fatigue strength explains number of times the applied stress loading will eventually cause fracture of material. The cemented carbide fatigue crack growth is linearly increases on threshold of cemented mean carbide grain size and mechanism of crack deflection ismore effective action for fatigue growth mechanisms [39] therefore coarsed hard metals are normally sensitive to fatigue behavior rather than binder mean free path which has fine-graded materials [23], [24]. From this observation, it is clear that individual deliberation of collective effects about altering binder content of carbide grain size is very important for the existence of different approaches between monotonic loading properties as considered for comparison [40].…”

“…This clearly identify the origin and propagation of cracks in work roll and identify critical zone where there is application of multiaxial principlesloading [33], [39]. Here,different analysis is doneand results compared to the measurements obtained from analysis of component failure.…”

“…It is important that presence of finer grains increases hardness. Therefore monitoring of crack propagation during fatigue loading is done by Fractography where theoretical models of crack growth behavior were evaluated [35], [39]. However, monitoring of fatigue crack growth (FCG) cannot be done by high-resolution under system described above without aspecial testing device [40].The testing of method of unnotched and notched using transverse rupture strengths at a given life (cycles) is used asestimatedmethod with three-point bending scheme [41], [10].…”

“…Tarragóa, et al (2017) investigated the dependence of effective fracture toughness based on estimateon of strength of WC-Co cemented carbides (hard metals) [39]. Authors opinion established that the strength behaviour of experimental done on WC-Co grades was based on R-curve critical failure [26], [39]. This is normally referred to as resistance to fatigue damage andexplains ability to absorb fracture energy by onset of failure.…”