Comparison between the RCF Performance of TiN- and TiO2-Laser Coated Ti64 Bearings

Abstract

The present work is a comparison between the rolling contact fatigue (RCF) of laser processed titanium bearings by using a scanning Nd:YAG Q-sw laser. TiN and TiO2 layers were produced on Ti6Al4V (Ti64) in a closed chamber in nitrogen and air atmosphere, respectively. The average thickness of the layers was 2 m in case of TiN and 0.8 m in case of TiO2. Both non-coated and coated bearings were RCF tested in under-water conditions and it was found that laser processing greatly improved their wear resistance and load capacity. Almost 50-fold and 20-fold increase in the wear resistance of the TiN and TiO2-coated bearings was observed after 7.7x106 cycles at a load of 150 N and 600 rpm. The mechanism responsible for this improvement is thought to be the 3-body-contact between the bearing elements and the small TiN and TiO2 debris, coming from the worn coating layers. The maximum load capability of the non-coated, TiN-coated and TiO2-coated bearings were 150 N, 200 N and 600 N. It is concluded that the higher load capacity of the TiO2 compared to the TiN coatings is due to its lower coefficient of friction.