Microstructural evolution of carbides and its effect on tribological properties of SAPS or HVOF sprayed NiCr-Cr3C2 coatings

The wear resistance of NiCr-Cr3C2 cermet coatings is highly dependent on the feature of hard carbides. In the present work, NiCr-Cr3C2 coatings were deposited by two typical high-velocity spraying methods including supersonic atmospheric plasma spraying (SAPS) and high velocity oxygen-fuel (HVOF) spraying. The microstructural evolution of hard carbides and its effect on the tribological properties of as-sprayed coatings were systematically studied. The results suggested that a large number of hard carbides dissolved with molten metal binder and then precipitated as the form of Cr23C6 from supersaturated molten metal binder, leading to the formation of interface transition zone and network carbides. Compared with HVOF-coating, although SAPS-coating had slightly higher porosity and lower hardness, a large number of large-size network carbides and a high content of interface transition zone resulted in a lower friction coefficient (0.14) and wear rate (0.77¡Á10-5 ¦Ìm/N¡¤s), owning to the high temperature and reducing atmosphere of supersonic plasma jet. The main wear mechanism of SAPS-/HVOF-coating was associated with abrasive and slight adhesive wear, and a small amount of?delamination was also observed on the wear track of SAPS-coating. Keywords: Carbides; Supersonic atmospheric plasma spraying; High velocity oxygen-fuel spraying; Tribological properties