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. 2024 Feb 13;17(4):870.
doi: 10.3390/ma17040870.

Tribological Properties of a Sliding Joint with an a-C:H:W Coating under Lubrication Conditions with PAO8 Oil and the Addition of 2% MoS2 Nanoparticles

Krystian Hadło  1 , Janusz Lubas  1 , Wojciech Szczypinski-Sala  2 , Agnieszka Tomala  3 , Dariusz Konieczny  1
Affiliations

Tribological Properties of a Sliding Joint with an a-C:H:W Coating under Lubrication Conditions with PAO8 Oil and the Addition of 2% MoS2 Nanoparticles

Krystian Hadło et al. Materials (Basel). .

Abstract

One of the promising methods for improving the durability and reliability of friction joints in combustion engines is the use of thin and hard coatings, including coatings based on amorphous DLC. The a-C:H:W coating was produced using the commercial PVD method. The tested tribological joints were made of AISI 4337 steel and SAE-48 bearing alloy (conformal contact) and AISI 4337 steel and valve shims (non-conformal contact). The contact area was lubricated with SAE 5W40 engine oil and PAO8 oil + 2 wt.% MoS2 nanoparticles. The objective of this work is to explore the influence of PAO8 + MoS2 on the tribological properties of a sliding joint with an a-C:H:W coating and the change in the properties of the oils. In the conformal contact, the lubrication of the a-C:H:W coating with PAO8 + MoS2 caused a significant increase in the friction resistance (than in) as compared to the joints with a quenching and tempering surface layer and lubricated SAE 5W40, while in the non-conformal contact, the lubrication of the a-C:H:W coating with PAO8 + MoS2 caused a decrease in the friction resistance and temperature of the contact area. The joints with the a-C:H:W coating were characterized by higher wear of the SAE-48 bearing alloy, as compared to the joints with the surface layer without coating (lubricated with SAE 5W40 oil-11-fold increase, PAO8 + MoS2-46-fold increase). The wear of valve shims with the a-C:H:W coating was significantly lower as compared to the wear of the commercial version of the valve shims (the difference between joints lubricated with SAE 5W40 oil and PAO8 + MoS2 was 12%, 36% and 29% for unit pressures of 10, 15 and 20 MPa). Lubrication of the a-C:H:W coating with PAO8 oil + MoS2 protected the sliding joints against seizing in non-conformal contact.

Keywords: DLC; MoS2; coating; engine oil; friction; surface layer; wear.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Elements of the tested joint: (a) ring specimen, (b) counterpart with SAE-48 bearing alloy (conformal contact), (c) counterpart—valve shims (non-conformal contact).
Figure 2
Figure 2
SEM cross—section a-C:H:W coating.
Figure 3
Figure 3
Photo of dispersed nanoparticles 50 h after homogenization.
Figure 4
Figure 4
Simplified scheme of the block-on-ring tester (a), the sliding joints—ring and block (b) and the joint in machine T-05 (c); n—rotational speed, P—load, T—resistive force.
Figure 5
Figure 5
Moment of friction during start-up in joints with conformal contact: (a) SAE 5W40, (b) PAO8 + MoS2.
Figure 6
Figure 6
Friction force vs. unit pressure at the end of the test in joints with conformal contact: (a) SAE 5W40, (b) PAO8 + MoS2.
Figure 7
Figure 7
Temperature in contact area vs. unit pressure at the end of the test in joints with conformal contact: (a) SAE 5W40, (b) PAO8 + MoS2.
Figure 8
Figure 8
Mass wear of the SAE-48 alloy during lubricated with: (a) 5W40, (b) PAO8 + MoS2.
Figure 9
Figure 9
Moment of friction during start-up in joints with non-conformal contact: (a) SAE 5W40, (b) PAO8 + MoS2.
Figure 10
Figure 10
Friction force vs. unit pressure at the end of the test in joints with non-conformal contact lubricated with (a) SAE 5W40 and (b) PAO8 + MoS2 (* seizure of sliding joint).
Figure 11
Figure 11
Temperature in contact area vs. unit pressure at the end of the test at joints with non-conformal contact lubricated with (a) SAE 5W40 and (b) PAO8 + MoS2 (* seizure of sliding joint).
Figure 12
Figure 12
Wear scar on counterpart valve shims lubricated with (a) SAE 5W40 and (b) PAO8 + MoS2 (* seizure of sliding joint).
Figure 13
Figure 13
Scuffing load of lubricants: (a) SAE 5W40, (b) PAO8 + MoS2.
Figure 14
Figure 14
Pressure of seizure of lubricants: (a) SAE 5W40, (b) PAO8 + MoS2.
Figure 15
Figure 15
Wear scar on the valve shims after operation in a non-conformal contact (pressing force of 3000 N) lubricated with (a) SAE 5W40 and (b) PAO8 + MoS2 (10× magnification).
See this image and copyright information in PMC

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