*Krishnanand Shukla1, Yashodhan P. Purandare1, Daniel A. L. Loch1, Arunprabhu A. Sugumaran1, Imran Khan2, Arutiun. P. Ehiasarian1, Papken. Eh Hovsepian1
1Sheffield Hallam University, Sheffield, United Kingdom; 2Zimmer-Biomet UK Limited, Swindon, United Kingdom
CoCrMo alloy, although an acceptable choice for metal-on-metal prosthetic implants, requires improvements in mechanical and tribological properties. In this work HIPIMS discharge has been utilized to perform low pressure plasma nitriding (HLPN). XRD studies revealed the formation of a compound layer consisting a desirable mixture of Co2-3N and Co4N phases and (111):(200)[43:57] texture. The achieved case depth of 2.5µm (4 hrs process time) was higher than obtained by a conventional plasma nitriding process (CPN) (2.1µm in 18 hours). Surface hardness of 23GPa was higher than obtained by CPN (20GPa) and compared to the bare alloy (7.9GPa). Consequently, a significant improvement in dry sliding wear resistance (KC=1.18×10-15m3N-1m-1) and lower friction coefficient (µ=0.6) could be achieved as compared to the untreated specimens ((KC=6.0×10-14m3N-1m-1) and µ=0.8). H/E and H3/E2 values of 0.078 and 0.135 respectively indicated that our HLPN process enhances toughness, impact load damping capability and endurance limit of the alloy, as confirmed also through impact load fatigue tests. Further, potentiodynamic polaristion tests (Hank’s solution) showed a significant improvement in corrosion resistance; Ecorr value of -218 mV was much nobler compared to untreated alloy (Ecorr=-775 mV). Achieved properties combined with the significant reduction in process time make HLPN a powerful technique for production.