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

Abstract The wear resistance of NiCr–Cr 3 C 2 cermet coatings is highly dependent on the feature of hard carbides. In the present work, NiCr–Cr 3 C 2 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 or diffused with molten metal binder and then precipitated as the form of Cr 23 C 6 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 × 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 track of SAPS-coating. The wear debris of both coatings mainly consisted of Cr 2 O 3 and NiCr 2 O 4 accompanied by a small amount of free graphite.