Rolling contact fatigue in high vacuum using ion plated nickel-copper-silver solid lubrication

Abstract

Ion plated, nickel-copper-silver coated steel ball bearings that were tested in rolling contact fatigue (RCF) experiments in high vacuum are presented in this article. ANSI T5 ball bearings were coated with approximately 10 nm of nickel-copper followed by 100 nm of silver using a dc ion plating process. The balls were then tested for RCF in vacuum in the 10−7 Torr range at 130 Hz rotational speed and at 4.1 GPa Hertzian contact stress. The significance of this work is in the extension of RCF testing to an ultrahigh vacuum (UHV) application using silver as a lubricant instead of oil. The effects of pressure and voltage on the ion plating process were also investigated using scanning electron microscopy and RCF life testing in UHV. Test results with a ball size of 5/16 in. in UHV show that deposition at voltages greater than 2.5 kV shortens the RCF life and introduces a unique failure mode. Voltage and pressure fluctuations during the deposition process result in significant thickness monitor measurement errors as well. A regulator control scheme that minimizes the process pressure overshoot is also simulated.

Influence of process parameters on rolling-contact-fatigue life of ion plated nickel–copper–silver lubrication

“…DoE test 12 used a process voltage of 3.5 kV, which is over twice that of test 3 and is well over the 0.7 kV range used by Chan and Chason. 10 Auger results of Fig. Iron and the other constituents from the stainless steel fixture used to support the balls inside the chamber will be present throughout the coating for process voltages above 2.5 kV.…”

“…The probe tip radius used for all measurements was 0.195 mm. 10 Using energy dispersive analysis and scanning electron microscopy (SEM), Danyluk and Dhingra 10 found trace amounts of stainless steel components in deposition tests above 2.5 kV, suggesting that metal atoms from the steel fixture inside the chamber are being sputtered off and deposited along with the nickel-copper-silver coating. In contrast, processes in the collisional-sheath regime are problematic in that one has no reliable method to account for electron-neutral collisions within the sheath.…”

“…10 Specifically, how does increased process voltage affect film composition, stress, and RCF life? 10 Specifically, how does increased process voltage affect film composition, stress, and RCF life?…”

“…We validated our MATLAB code by reproducing the results of Chan and Chason 1 for defect concentration and stress to within 5% of their results. 10. The evolution of argon ion concentration C Ar z; t ð Þ for DoE run 3 is presented in Fig.…”

Rolling Contact Fatigue in Ultra High Vacuum

“…For contact stress of 2.41 GPa, they report slower spall growth in ANSI M50 compared with either ANSI M50NiL or ANSI 52100 due to material composition and processing. Danyluk and Dhingra (2011) observe two types of failures related to RCF testing in ultra-high vacuum: coating depletion and surface spall. Solid film nickel-copper-silver lubrication was applied to ball bearings over a range of process voltage and pressure using a physical vapor deposition ion plating process.…”