Structure and wear behaviour of nanostructured and ultrafine HVOF spraying WC-17Co coatings

Nanostructured and ultrafine WC-17Co coatings have been prepared by means of the high velocity oxyfuel (HVOF) technique. The structures of the two feedstock powders were analysed. The wear resistances at the elevated temperature (600 degrees C) of the two coatings were compared using GCr15 steel as a counterpart in sliding wear tests. The results show that the WC particles are of nanosize, ranging from 50 to 500 nm. Finer subparticles of 2-5 nm are also found, composed of the nanosized WC particles. These subparticles can act as crystallising nuclei and make the grains much finer during the HVOF spraying process, which is beneficial to the formation of nanostructure in the coating. The wear resistance and fracture toughness of the nanostructured coatings at elevated temperatures are better than that of ultrafine coatings.