Microstructural aspects on wear of cemented carbides

Sammanfattning: Cemented carbides are known to be very wear resistant and are therefore often usedin applications involving surface damage and wear. The work presented hereinvestigates the coupling between the microstructure and some fundamental wearand deformation mechanisms typical for cemented carbides. A model to calculate the indentation hardness of cemented-carbides from thecarbide grain size and Co-content has been developed. The model predicts thehardness with 85 % accuracy for compositions ranging from 0 to 40 % Co andcarbide grains between 0.07 to 5μm. The anisotropic nature of WC has been used to explain the abrasive wearmechanisms of WC single crystals and cemented carbides. The microstructure and tribological properties of binderless carbides havebeen examined in detail. It is shown that the wear properties are closely connected tothe choice of γ-phase and that the binderless carbides behave more like cemented carbides than ceramics. A descriptive model for mild abrasion of cemented carbides is proposed. Themodel explains why fairly different cemented carbides behave very similarly whenabraded mildly. The importance of the binder metal for the performance of cemented carbidesin applications involving combined corrosive and mechanical wear has beeninvestigated. The results show that the binder should be corrosion resistant in itselfbut also be able to control the behaviour of WC. Wear phenomena on cemented carbide face seals have been analysed withvarious analytical tools including focused ion beam and transmission electronmicroscopy. It is shown that it is possible to form a several micron thick nano-crystalline (WC-Co) tribofilm during dry operation.

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