The influence of size and distribution of graphite on the friction and wear behavior of Ni–graphite coatings

• The size of graphite particles affects the tribological property of Ni–graphite coatings.
• The average size of graphite particles is much finer in SAPS-coating.
• The fine graphite particles help to form a homogeneous and continuous tribofilm.

In this work, the METCO 307 (75 wt.% Ni + 25 wt.% graphite, M307) abradable seal coatings were deposited by conventional atmospheric plasma spraying system (APS) and high efficiency supersonic atmospheric plasma spraying system (SAPS), respectively. Comparative dry reciprocating sliding wear experiments on the as-sprayed coatings against a 440-C stainless steel ball were conducted on the CETR UMT-3 friction and wear tester. The results indicated that the average width and length of lubrication phase (graphite) were 3.54 ± 0.06 and 7.51 ± 0.13 μm in the SAPS-coating, which were lower than 4.15 ± 0.11 and 8.03 ± 0.09 μm in the APS-coating. The fine graphite phase improved the formation of homogeneous and continuous tribofilm during the reciprocating sliding friction process. The track depth of APS-coating increased from 0.093 to 0.161 mm, while that of SAPS-coating increased from 0.087 to 0.151 mm when the test temperature rose from 25 to 400 °C, indicating that the SAPS-coatings had a higher wear resistance.