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

The wear resistance of NiCr–Cr 3 C 2 cermet coatings is highly dependent on the feature of 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 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 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-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 Cr 2 O 3 and NiCr 2 O 4 accompanied by a small amount of free graphite. Image 1 • Structural evolution of carbides in SAPS-/HVOF-coating was comparatively studied. • Network carbides were helpful to improve the wear resistance of NiCr–Cr 3 C 2 coating. • SAPS-coating with large-sized network carbides showed a better wear resistance. [ABSTRACT FROM AUTHOR]