ABRASION RESISTANCE OF NANOSTRUCTURED AND CONVENTIONAL CEMENTED CARBIDES

The abrasion resistance of nanostructured WC-Co composites, synthesize d by a novel spray conversion method, is determined and compared with that of conventional materials. Scratching by diamond indenter and abr asion by hard (diamond), soft (zirconia) and intermediate (SiC) abrasi ves was investigated. The size of the scratch formed by the diamond is simply related to the hardness of the composite. Plastic deformation, fracture and fragmentation of the WC grains increase with their size. Nanoscale composites show purely ductile scratch formation. Nanocompo sites possess an abrasion resistance approximately double that of the most resistant conventional material: this is a higher gain than the i ncrease in hardness which is at most 23%. This large gain is due to a specific grain size effect on abrasion resistance in the case of diamo nd and SiC abrasive and to a very rapid increase of abrasion resistanc e with hardness in the case of the softer (SiC and ZrO2) abrasives. Th e observation of the abraded surfaces of conventional composites repro duced the known mechanisms: plastic deformation and fracture of WC gra ins by hard abrasives; removal of binder phase and fall-out of WC by s oft abrasives. Magnetic fields from the ferromagnetic Co prevent the o bservation of abrasion mechanisms in the very fine-structured nanocomp osites.