Friction and wear behaviour of WC–Co–Cr3C2–VC cemented carbides obtained from nanocrystalline mixtures

doi:10.1016/j.wear.2011.07.012

Wear

Volume 272, Issue 1, 3 October 2011, Pages 62-68

https://doi.org/10.1016/j.wear.2011.07.012 Get rights and content

Abstract

The effect of adding Cr₃C_2, VC or a mixture of both as a grain growth inhibitors to cemented carbides obtained from WC–12 wt.%Co nanocrystalline mixtures on the behaviour of friction and dry sliding wear have been studied. All the wear tests were performed on a tribometer with ball on disc configuration, using a WC–6 wt.%Co ball as a counterpart with normal contact loads of 40 and 60 N, sliding distance of 2000 m and a sliding speed of 0.1 m/s. A significant reduction in the wear rates was observed by the effect of the aforementioned additives, in particular for the VC, which showed an increase in the wear resistance of the order of 90%. The analysis of wear and surface damage were correlated to the observed behaviour.

Highlights

► Tribological behaviour of WC-12Co-Cr₃C₂-VC cemented carbides has been studied. ► It has been proven that the presence of inhibitors reduces friction coefficient values. ► An important reduction in wear rates with the addition of inhibitors has been found. ► The addition of VC has allowed to increase wear resistance by more than 90%. ► A possible surface damage sequence has been established.

Introduction

WC–Co cemented carbides are universally used in many industrial applications such as: high-speed machining [1], drilling [2], mining [3], woodworking [4], cutting [5], [6], forming and machining of metals [7], [8]. This wide range of applications is due to its special combination of properties: high hardness, toughness, resistance to compression deformation and wear resistance [9]. The improvement in the toughness–hardness relationship of the submicron and ultrafine grades [10], [11], [12], with the need for micrometer dimensions and rounded shapes tools, has led to its introduction and rapid expansion in the market for special applications as microdrilling for printed circuit boards (PCBs) [12]. In this application, the use of ultrafine and near-nanostructured grades allows to increase the drilling precision and extend the tool lifetime due to the improvements in the wear resistance [12].

The wear behaviour of cemented carbides WC–Co is directly and mainly related to its chemical composition and microstructure [13]. For this reason and depending on each specific application, their properties can be tuned according to its cobalt content, size and quality of the starting powder, consolidation techniques and use of grain growth additive inhibitors [12], [14], [15], [16], [17]. The wear resistance of these materials generally increases by the reduction of cobalt content and by decreasing the grain size [16], [17], [18], [19], [20]. Therefore the use of nanostructured cemented carbides opens new possibilities in wear applications, either by increasing the useful lifetime or its applications in severe wear conditions.

Dry sliding wear in conventional grades of WC–Co has been studied in different laboratory conditions and tribosystem configurations [19], [20], [21], [22], [23], [24], [25], [26], however, the literature reported few studies in which the behaviour of either ultrafine or nanosized grades is evaluated. Jia and Fisher [19] are the only authors who study the wear behaviour of nanosized grain carbide. They concluded that the wear resistance of nanostructured WC–Co is higher than that of conventional grades in proportion to their hardness, but suggest that the most effective technique to increase sliding wear resistance is to reduce the cobalt content. Wear behaviour of nanostructured WC–Co coatings have been studied for numerous authors but its superiority compared to conventional coatings is not clear [27], [28], [29], [30], [31], [32].

In this context, more studies that contribute to a better understanding of a wear response of near-nanoscale cemented carbides are necessary. In this paper, the tribological behaviour of WC–12 wt.%Co cemented carbides obtained from nanocrystalline mixture with addition of grain growth inhibitors Cr₃C₂ and VC have been studied.

Section snippets

Experimental procedure

A commercial nanocrystalline mixture of WC–12Co developed by Inframat Advanced Materials, with a WC particle size in the range 40–80 nm was used as a raw base powder. For this issue, 1 wt.%Cr₃C₂, 1 wt.%VC or a mixture of 0.5 wt.%Cr₃C₂ + 0.5 wt.%VC was added to control the WC grain growth during processing. These mixtures were consolidated by conventional liquid phase vacuum sintering at 1400 °C for 30 min [15]. Sample designation, composition and properties of the cemented carbides studied are shown in

Friction coefficient

During wear tests, both imposed normal contact force (F_n) and the resulting friction tangential force (F_t) were continuously recorded, and accordingly the friction coefficient (μ) was determined as the ratio of F_t and F_n.

As shown in Fig. 2a, when using 40 N contact load, both N and NCr materials show an increasing friction coefficient in the first meters of sliding (stage 1) This behaviour extends up to 400 m and 200 m, respectively. This stage is associated with an abrupt removal of fragments of

Conclusions

The results obtained in this study point out the significant influence of grain growth inhibitors in the friction and wear behaviour of cemented carbides.

It has been proven that the presence of inhibitors significantly reduces friction coefficient value and limits the increase in this parameter when increasing the contact load.

A significant reduction in wear rates with the addition of inhibitors was found. This was especially noticeable for the case of VC, which allowed to increase wear

Acknowledgements

The authors would like to thank the Ministry of Education and Science, and the support received through the Projects MAT2006-12945-C03-02 and MAT2009-14144-C03-02, as well as the AECI for the realization of the doctoral thesis by L. Espinosa in the ITM of the UPV.

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Friction and wear behaviour of WC–Co–Cr3C2–VC cemented carbides obtained from nanocrystalline mixtures

Abstract

Highlights

Introduction

Section snippets

Experimental procedure

Friction coefficient

Conclusions

Acknowledgements

Int. J. Refract. Met. Hard Mater.

Int. J. Refract. Met. Hard Mater.

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Friction and wear behaviour of WC–Co–Cr₃C₂–VC cemented carbides obtained from nanocrystalline mixtures