We investigate the thermal behavior of the friction property of ultra-thin perfluoropolyether (PFPE) lubricant film on diamond-like carbon (DLC) overcoats of magnetic disks. We use a newly developed pin-on-disk tester with laser irradiation heating. Results show that the friction coefficient of a lubricated DLC surface with Z-tetraol decreased with increased temperature, while for lubricated disks with Z-03, it gradually decreased at around 120°C and increased over 120°C. This minimal point may indicate the transition temperature. The friction coefficient of both lubricant films on the DLC surface varied with the kinematic viscosity of the lubricant materials, and decreasing the kinematic viscosity decreased the friction coefficient.
This study investigated how the surface roughness of steel disks coated with a Si-containing diamond-like carbon (DLC-Si) film affects the dependence of the friction characteristics, in an oil-lubricated condition via the use of friction experiments and numerical analyses using mixed lubrication models. This study clearly demonstrated that a DLC-Si film with a surface roughness of RzJIS = 3 to 4 μm was an effective means of suppressing frictional vibration caused by stick-slip. In addition to finding that the surface roughness of steel disks coated with DLC-Si film could be used as a design guideline for the sliding surface of an electromagnetic clutch to provide excellent μ-v characteristics, it was also found that providing the mating plate with micro grooves that have a depth of 10 μm and a pitch of about 100 μm was an effective means of improving the friction characteristics. The results of this study suggested that the surface roughness and the micro grooves maintain solid contact even if the formation of oil film is enhanced as the sliding velocity increases, since these results in boundary lubrication.
Fuel economy is a major challenge for the automotive industry. A key way to improve lubricant fuel efficiency is by using polymers as viscosity index improvers to maximise the viscosity index of the lubricants. The viscosity index of automotive lubricants has an upper limit of around 250 because usage of high treat rates can lead to shear stability and flash point issues. To overcome this, the concept of two phase lubricants was reported in former literature but the practical application had not been examined. In this paper, the practical application with an additional ability to control viscosity and separation temperature simultaneously of a two phase lubricant is reported. It is possible to formulate a two phase lubricant with mineral or synthetic base oil and polyalkylene glycol to achieve viscosity index of 500 and keeping the properties of shear stability and flash point on a competitive level as of commercial single phase lubricants. Also, there is little evidence of issues with the lubrication properties. It was shown that additions of Di-isononyl adipate acting as a control element simultaneously control the viscosity and separating temperature of the two phase lubricants.