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

Abstract

The wear resistance of NiCr–Cr3C2 cermet coatings is highly dependent on the feature of 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 carbides and its effect on the tribological properties of as-sprayed coatings were systematically studied. The results suggested that a large number of carbides dissolved or diffused 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-sized network carbides and a high content of interface transition zone resulted in a lower friction coefficient (0.14) and wear rate (0.77 × 10−5 μm/N·s) under heavy load, 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 tracks of SAPS-coating. The wear debris of both coatings mainly consisted of Cr2O3 and NiCr2O4 accompanied by a small amount of free graphite.