Abstract
Nanocrystalline coatings have a high potential for various engineering applications, e.g. against wear of rolls in the paper fabrication and as corrosion protection. Using vacuum plasma spray (VPS) and high velocity oxy‐fuel (HVOF) spray techniques, coating materials are exposed to high flame temperatures only for less than a millisecond. Therefore, high‐energy milled powders can be used as feedstock material without losing its nanocrystalline microstructure during the thermal spray process. In this way, homogeneous, dense nanocrystalline coatings can be produced, which show enhanced hardness, thus obtaining promising superior wear resistance. In the present study, (Ti,Mo)(C,N)‐45vol.%NiCo nanocrystalline coatings were prepared by VPS‐ and HVOF‐spraying of high‐energy milled powders. Abrasive wear tests JIS H 8615 with varying number of strokes and scratch tests with a Vickers indenter were applied to produce wear traces on the polished surfaces of the nanocrystalline coatings. Abrasive wear behaviour was analyzed by investigating the surface morphologies with optical microscopy (OM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Experimental results indicate that the VPS‐coating has higher abrasive wear resistance than the HVOF‐coating according to the JIS H8615 test. The abrasive wear mechanism of VPS‐sprayed nanocrystalline coatings can be delineated as cutting plus ploughing. For HVOF‐sprayed nanocrystalline coatings the abrasive wear mechanism can be described as cutting plus material delamination.