Koenraad Bonny

Tribological Characteristics of WC-Ni and WC-Co Cemented Carbide in Dry Reciprocating Sliding Contact

Four WC-based cemented carbides produced by liquid phase sintering with different binder composition and similar carbide grain size were tested in order to evaluate their dry reciprocating sliding friction and wear behavior against WC-6 wt.%Co cemented carbide. The pin-on-flat wear experiments were executed on a Plint TE77 tribometer using normal contact loads of 15 N up to 35 N and a sliding velocity of 0.3 m/s. Analysis of the wear tracks revealed several wear mechanisms; i.e., polishing of WC grains, abrasion, adhesion, formation of wear debris layer, and removal of the surface binder from between the WC grains. Higher contact load increased the wear volume and slightly decreased the friction coefficient. The hardness as well as the type and the amount of binder phase were found to affect the wear resistance significantly. One WC-Ni alloy exhibited superior tribological characteristics compared to the other grades.

Influence of Surface Finishing and Binder Phase on Friction and Wear of WC Based Hardmetals

At present, cobalt is the most commonly used binder material in tungsten carbide based hardmetals. Current research on sliding wear performance of these cemented carbides, however, reveals promising results for nickel binder as well. Test samples of WC-Co and WC-Ni hardmetals have been machined and surface finished by wire-EDM and grinding. From comparative dry sliding pin-on-plate experiments on wire-EDM’ed, ground and polished grades, correlations are derived between wear volume loss and friction on the one hand and contact pressure, sliding distance, binder phase and microstructure on the other hand. The lowest wear levels are encountered with polished cemented carbides. The EDM induced surface modification turns out to deteriorate wear resistance, especially during the running-in stage of sliding. These findings are in agreement with Xray diffraction measurements of the residual stress level in the WC phase.

Reciprocating friction and wear behavior of WC-Co based cemented carbides manufactured by electro-discharge machining

Tungsten carbide based hardmetals with cobalt binder phase are widely used in engineering industries for their excellent mechanical properties and outstanding wear performance. Reciprocative sliding wear behaviour of a number of WC-Co based hardmetal grades was investigated using a small-scale pin-on-plate tribometer. Test samples were manufactured by electro-discharge machining (EDM) with various surface finishing regimes. SEM topographies and cross-section views of the cemented carbides were obtained both before and after dry friction tests, revealing distinctive wear mechanisms. The generated wear loss was quantified topographically using surface scanning equipment. Wear debris particles were collected and examined by EDX and TEM analysis. Based on experimental results, the execution of consecutive gradually finer EDM cutting steps was found to considerably enhance wear performance. Furthermore, a significant influence of contact load, sliding movement duration, application of lubricant and wear debris formation on wear rate and friction was established.

Edge Effects in Sliding Wear Behavior of ZrO2-WC Composites and WC-Co Cemented Carbides

A trend in the development of WC based cemented carbides and zirconia based ceramic composites is grain size refinement and more narrow grain size distributions of the starting powder, in order to accomplish higher hardness and abrasive wear resistance. The current work reports the results of dry sliding wear experiments on laboratory-made electrically conductive ZrO2-WC composites and commercially available WC-Co based cemented carbides, which have been manufactured and finished by rough cutting wire EDM with consecutive execution of gradually finer EDM regimes. Tribological data are obtained using a small-scale pin-on-plate test rig. Wear tracks are analyzed by surface scanning topography and scanning electron microscopy, revealing that the outer extensions of the wear tracks exhibit some differences in wear behavior compared to the central parts.

Self-Healing of a Soft Primer Coating Caused by Plasticization during Sliding against UHMWPE

Sliding of a soft primer coating at 150 MPa under flat-on-flat conditions reveals the capability of defects reparation, which cannot be simulated on a standardized laboratory test with concentrated contact and test conditions. The contributions of plasticization, softening and melting are discussed.

Influence of secondary electro-conductive phases on sliding wear performance of zirconia based ceramic composites

Zirconia-based ceramic composites such as ZrO2-WC, ZrO2-TiCN and ZrO2-TiN, are suitable for wire-EDM, due to their sufficiently electro-conductive secondary phases inside. Thus, the material removal technique of EDM to shape complex geometry materials economically and with high accuracy, irrespective of mechanical properties, could be successfully employed on these ceramics. Samples of these ZrO2-based ceramics were developed in laboratory and manufactured and surface finished by wire-EDM. Reciprocative dry sliding pin-on-plate experiments revealed that the ZrO2-WC composite exhibits better tribological characteristics in comparison with the composites of ZrO2-TiCN and ZrO2-TiN. Furthermore, topographies and cross-sectional views of worn surfaces were analyzed by SEM, revealing that the secondary phase inside the investigated composites governs the wear mechanism.

Heating Effects in WC-Co Cemented Carbides as a Result of Reciprocative Dry Sliding Friction

WC-Co based cemented carbides are widely used in technical applications, in which they are exposed to complex thermo-mechanical loadings. Previous research work has demonstrated that these materials exhibit a lifetime-limiting fatigue sensitivity at room temperature. This investigation is focused on the influence of heating as a result of friction of pin-on-plate tribocouples. WC-Co samples have been manufactured and surface finished by wire-EDM and grinding. Reciprocative dry friction experiments are performed under various loading conditions and sliding velocities. Correlations are established between the bulk temperature rise of the test samples and the imposed test conditions, material properties, surface conditions and coefficient of friction. Topographies and cross-section views of the tested samples were examined by SEM, revealing temperature dependent wear mechanisms, including binder phase modification.