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

Abstract

Articles you may be interested inKinetic model for dependence of thin film stress on growth rate, temperature, and microstructure J. Appl. Phys. 111, 083520 (2012); 10.1063/1.4704683Rolling contact fatigue in high vacuum using ion plated nickel-copper-silver solid lubricationThe rotation of ripple pattern and the shape of the collision cascade in ion sputtered thin metal films J. Appl. Phys.In this paper, we present a connection between argon ion flux, element-mixing, and rolling contact fatigue (RCF) life of a thin film nickel-copper-silver lubricant on ball bearings. The film is deposited on the balls using an ion plating process and tested for RCF in high vacuum. The ion flux is measured using a Langmuir probe and the plane stress within the film during deposition is calculated using a thin film model. Experiments reveal that there is an inverse relationship between ion flux and RCF life for most deposition voltage and pressure combinations tested, specifically, 15.5-18.5 mTorr and 1.5-3.5 kV. For voltages up to 2.5 kV, RCF life decreases as ion flux increases due to increased compressive stress within the film, reaching as high as 2.6 GPa. For voltages between 2.5 and 3.5 kV, interlayer mixing of nickel and copper with the silver layer reduces RCF life due to contamination, even as ion flux and corresponding film compressive stress are reduced. A Monte Carlo-based simulation tool, SRIM TM is used to track collision cascades of the argon ions and metal atoms within the coating layers. At process voltages above 2.5 kV we observe elemental mixing of copper and nickel with the silver layer using Auger electron spectroscopy of coated steel and Si 3 N 4 balls. The authors conclude that an ion flux greater than 5.0 Â 10 14 cm À2 s À1 leads to reduced RCF life due to high film stress. In addition, process voltages greater than 2.5 kV also reduce RCF life due to contamination and interlayer mixing of nickel and copper within the silver layer.

Rolling Contact Fatigue in Ultra High Vacuum

“…The results of Figures 3 and 4 suggest interlayer mixing and coating contamination during the deposition process which is likely to influence the lubrication properties of the film, and ultimately the RCF life. For more information concerning thin film diagnostics and deposition plasma diagnostics related to RCF life, see (Danyluk and Dhingra, 2012b). …”