Effect of Oxygen on the Self-formation of Carbonaceous Tribo-layer with Carbon Nitride Coatings under a Nitrogen Atmosphere

Impact of Relative Humidity on the Formation of Low-Frictional Interface and its Continuity in Tribological Systems with Hydrogenated Carbon Nitride Coatings

“…The spectra showed a growth in the D peak and a shift in the G peak toward a higher wave shift compared with that of the initial CN x :H. This change in the Raman spectrum indicates different amorphous structure of the carbonaceous tribolayer from the initial coatings, indicating a transformation into a more graphitic structure. This spectral pro le is similar to that of low-frictional tribolayers with nanometer-scale thickness (less than 10 nm) previously reported in our studies, suggesting a comparable carbon structure [19,[22][23][24]. Similar to those earlier ndings, the carbonaceous tribolayer detected here is also exceedingly thin for optical microscopy detection, supporting its identity as the critical low-frictional tribolayer essential for reducing friction in CN x :H systems, with an inferred thickness of less than 10 nm [19,24].…”

“…7 under nitrogen atmospheres with low relative humidity could also be attributed to the desorption of hydrogen content from the friction surface of CN x :H. As discussed in Section 3.1, low friction continued up to 10,000 cycles even at < 0.2% RH, which represents a longer low-friction period compared with that observed in the nitrogen atmosphere at less than 0.2-0.25% RH (less than 5,000 cycles). This longer duration of low friction in the presence of higher oxygen concentrations may be due to the impact of oxygen on the structural changes of carbon [22,23,38]. However, the continuous formation of the low-frictional carbonaceous tribolayer was achieved even in nitrogen atmosphere with minimal oxygen concentration (< 300 ppm O 2 ), and the durability of low friction signi cantly enhanced within the optimal relative humidity range of 0.25-1.0% RH (Fig.…”

“…Carbon nitride (CN x , a-C:N) and hydrogenated carbon nitride (CN x :H, a-C:N:H) represent promising types of hard carbon coatings known for their excellent tribological properties in dry, lubrication-free environments [17,18]. Numerous studies have reported that CN x and CN x :H coatings consistently achieve a stable friction coe cient of less than 0.05 in dry environments such as nitrogen atmosphere [19][20][21][22][23][24][25][26][27][28]. A critical factor in achieving low friction within these tribological systems involves the formation of a low-frictional carbonaceous tribolayer on the mating surface.…”

“…This tribolayer, which has a nanometer-scale thickness (approximately 10 nm thickness or less) undetectable by optical microscopy [19,24], differs markedly from the thicker graphite-rich lms typically identi ed as low-shear tribo lms in DLC coatings [11][12][13][14][15][16]. Additionally, CN x :H coatings exhibit lower and more stable friction and a signi cantly reduced speci c wear rate of mating material (10 − 8 mm 3 /Nžm order or less) compared with CN x coatings across a broad spectrum of environmental conditions, including relative humidity (RH) and oxygen concentration [23]. On the friction surface of CN x coatings, the desorption of nitrogen atoms from the coating structure is considered to facilitate the transformation of the carbon structure [26,28].…”

Triboemission of hydrocarbon molecules from diamond-like carbon friction interface induces atomic-scale wear

“…The hydrogenated DLC coating on the silicon wafer is deposited using radio-frequency plasma-enhanced chemical vapor deposition with a mixture of CH 4 and N 2 gas. Details of the deposition parameters were reported previously ( 32 ). The total thickness of the hydrogenated DLC coating on the substrate is 1200 nm.…”