Fatigue life and mechanical behaviors of bearing steel by nitrogen plasma immersion ion implantation

Rolling contact fatigue (RCF) performance and mechanical characteristics of nitrogen plasma immersion ion implantation (PIII) on AISI521 00 bearing steel surface has been investigated using a conventional three ball-on-rod rig. Testing investigations include optical microscopy (OM), friction and wear behavior, rolling contact fatigue life, and nano-indentation measurements. Results indicate that the rolling elements failed at the surface or near-surface layer. Moreover, an appreciable amount of surface wear was observed on the surface of the rolling elements after RCF tests. The maximum microhardness of treated samples is nearly twice as that of substrate. The friction coefficient of the treated samples is decreased from 0.90 to 0.15. The L-10 life of the treated specimens increase by 99.6% and L-50 life enhance by 236.3% at a Hertzian stress level of 5.1 GPa and 90% confidence level, respectively. OM morphology results indicate that the surface roughness, processing parameters, and inner defects play an important role in surface and near-surface initiated RCF. This improvement of fatigue and mechanical performance is attributed to form a combination of nitrides phase structure and residual compressive stress during the nitrogen-PIII process. (C) 2006 Elsevier B.V. All rights reserved.