TiN/NbN Nanoscale Multilayer Coatings Deposited by High Power Impulse Magnetron Sputtering to Protect Medical-Grade CoCrMo Alloys

• Published in: Coatings (Basel) Vol. 11; no. 7; p. 867
• Main Authors: Sugumaran, Arunprabhu Arunachalam, Purandare, Yashodhan, Shukla, Krishnanand, Khan, Imran, Ehiasarian, Arutiun, Hovsepian, Papken
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.07.2021
• Subjects: Biocompatibility; Bonding strength; Cobalt base alloys; Corrosion currents; Corrosion prevention; Corrosion resistance; Crack initiation; Debris; Direct current; Failure mechanisms; Impact tests; Inductively coupled plasma mass spectrometry; Ion beams; Leaching; Magnetron sputtering; Mass spectrometry; Multilayers; Niobium nitride; Pitting (corrosion); Protective coatings; Scratch tests; Sliding friction; Substrates; Transplants & implants; Wear particles; X ray analysis; United Kingdom > UK; United States > US; Austria
• ISSN: 2079-6412; 2079-6412
• DOI: 10.3390/coatings11070867

This study describes the performance of nanoscale multilayer TiN/NbN coatings deposited on CoCrMo medical-grade alloys by utilising novel mixed high power impulse magnetron sputtering (HIPIMS) and direct current unbalanced magnetron sputtering (UBM) technique in an industrial size vacuum coater. Scanning electron microscopy analysis showed that these coatings were extremely dense without any intercolumnar voids. The coating exhibited high hardness of 28 GPa, as well as low friction and wear coefficient of 0.7 and 1.4 × 10−14 m3·N−1·m−1, respectively, as compared to the bare material. Scratch tests revealed superior coating to substrate adhesion due to the HIPIMS etching prior to coating deposition. Energy-dispersive X-ray analysis of the wear debris generated during the impact test together with focused ion beam cross-section analysis in different locations of the impact crater revealed the coating failure mechanism and further confirmed the excellent coating to substrate bonding strength. Potentiodynamic polarisation tests in NaCl and Hank’s solutions revealed the clear passivation behaviour, several orders of magnitude lower corrosion currents, and high pitting potentials of the coating, which guarantee excellent protection to the base alloy in such aggressive environments. Inductively coupled plasma mass spectrometry analysis of Hank’s solution containing corrosion debris of the coated sample revealed that the leaching of harmful metal ions from the base material was reduced to below the detection limit of the technique, thus demonstrating the high barrier properties of the coating.