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6309 |
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Microstructural evolution of carbides and effect on tribological properties of SAPS and HVOF sprayed NiCr-Cr3C2 coatings |
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Qi Liu* / Xi'an Jiaotong University, P.R. China Y Bai / Xi'an Jiaotong University, P.R. China G.Z. Ma/ Army Academy of Armored Forces, P.R. China M. Liu/ Army Academy of Armored Forces, P.R. China Y.W. Sun/ Xi'an Jiaotong University, P.R. China |
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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-speed 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 Cr23C6 from supersaturated molten metal binder resulting in the formation of interface transition zone and network carbides. Compared with HVOF-coating, although SAPS-coating had slightly higher porosity and lower hardness, the large number and size of network carbides and the high content of interface transition zone led to a lower friction coefficient (0.14) and wear rate (0.77 × 10-5 ¼m/N"s) under heavy load due to the high temperature and reducing atmosphere of supersonic plasma jet. The main wear mechanism of SAPS- or 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 Cr2O3 and NiCr2O4 accompanied by a small amount of free graphite. |