Massive nitrogen super-saturation into CoCrMo Alloys for improvement of tribological performance

The cobalt-chromium-molybdenum (CoCrMo) superalloys have been utilized in the dental, knee, and hip arthroplasty applications because of their unique combination of high strength, high wear and corrosion resistance. A massive nitrogen supersaturation (MNS) process was proposed as a surface treatment to improve these strength, hardness and ductility, further needed for hip replacement and dental prosthesis. CoCrMo disc specimens were prepared for plasma immersion nitriding at 673 K for 21.6 ks by 50 Pa. The nitrogen solute uniformly distributed in the MNS-layer with the average content of 5 mass%. Higher surface hardness than 1550 HV was attained under application of 10 N. The maximum friction coefficient was halved before and after MNS and this low frictional state with μ< 0.45 was preserved although the sliding condition by 0.1 m/s.