Low energy isothermal plasma-immersion ion implantation of nitrogen for enhanced hardness of AISI 52100 ball bearing steel

Plasma immersion ion implantation (PIII) is an advanced, plasma-assisted surface engineering technique to enhance resistance to wear, corrosion, etc. The present study concerns PIII of nitrogen ions in AISI 52100 ball bearing steel at low energy (∼1 keV) to increase the hardness. The substrate temperature was independently varied up to 500°C with a heater to facilitate diffusion of the implanted ions during PIII. Microhardness measurements reveal a significant increase in hardness within the implanted zone or case extending up to approximately 40 μm following PIII carried out isothermally at a temperature between 300 and 500°C for 3–5 h. X-ray diffraction analysis indicates that PIII results in the formation of three varieties of iron-nitrides, which have also been detected by X-ray photoelectron spectroscopy (XPS). However, these nitrides are too fine to be resolved under the optical microscope. Auger electron spectroscopy (AES) shows that the nitrogen penetration depth is greater than the case depth, determined separately by a cross-sectional microstructural study and hardness measurements. Finally, a simple kinetic analysis reveals that nitrogen diffusivity in the present PIII study is an order of magnitude faster than the relevant diffusion rate of nitrogen in steel.