Characterisation of wear properties of ultrafine-grained hardmetals using a special abrasive wheel test

Abstract

Three-body abrasive wear tests were carried out on super ultrafine-grained hardmetals (WC intercept length about 0.2 μm) with different Fe, Ni, Co binder systems, on hardmetals with Co binder and on standard materials with coarser WC grains. Apart from the standard materials, the hardmetals were all produced in laboratory scale from commercial nanocrystalline WC powders from different companies. The practical application of these hardmetals is in the field of cutting dry wood. The main purposes of this work were to characterise the wear properties of the produced grades and to derive predictions from laboratory wear tests regarding practical applications. Therefore a new wear test apparatus was built. The wear results showed a logarithmic correlation with hardness and a threshold to the low wear region, which was exceeded by some grades, at binder mean free paths of less than 40 nm. Moreover the laboratory wear results correlate well with results from field testing. A tribofilm was found on the worn surface and characterised by scanning electron microscope (SEM), AFM and TEM. In an analysis of the wear mechanisms the role of this tribofilm must be considered.