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

Arunprabhu Arunachalam Sugumaran,Imran Khan,Yashodhan Purandare,Papken Hovsepian,Arutiun Ehiasarian,Krishnanand Shukla

doi:10.3390/coatings11070867

Abstract

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.

Highlights

CoCrMo alloys have been widely used for biomedical applications such as knee and hip replacement joints due to their excellent biocompatibility, mechanical, and corrosion properties
The reduction of Co, Cr, and Mo ion release from CoCrMo knee implant has been achieved by depositing CrN/NbN nanoscale multilayer structured coatings by high power impulse magnetron sputtering (HIPIMS) [9]
The aim of this work was to widen the scope of specialised protective coatings for medical-grade CoCrMo alloys by development and detailed investigation of the mechanical, tribological, and corrosion behaviour of TiN/NbN multilayer coatings utilising nanoscale multilayer/superlattice structure

Summary

Introduction

CoCrMo alloys have been widely used for biomedical applications such as knee and hip replacement joints due to their excellent biocompatibility, mechanical, and corrosion properties. It has been reported that the performance of these implants can be enhanced by depositing suitable monolithic or multilayer structured protective coatings. Neumann et al discussed the potential application of arc-deposited monolithically grown binary nitride based on biocompatible metals such as TiNbN coating for SS implants [7]. Hamelynck et al found a huge reduction of Cr ion release from CoCrMo hip component due to TiNbN coating deposited by physical vapour deposition [8]. The reduction of Co, Cr, and Mo ion release from CoCrMo knee implant has been achieved by depositing CrN/NbN nanoscale multilayer structured coatings by high power impulse magnetron sputtering (HIPIMS) [9]. To the best of the authors’ knowledge, the literature available on the surface engineering of CoCrMo alloys by HIPIMS is scarce

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