Ti/TiN/HA coating on Ti–6Al–4V for biomedical applications

Abstract

An unbalanced physical vapor deposition (PVD) magnetron sputtering technique was used to deposit a titanium/titanium nitride/hydroxyapatite (Ti/TiN/HA) multilayer coating on Ti–6Al–4V. The Taguchi optimization method with an orthogonal array of L9 was utilized to determine the optimal conditions of coating for better surface integrity. The effects of the temperature, DC bias voltage, nitrogen flow rate, and DC power on the adhesion strength, coefficient of friction, surface hardness, and surface roughness were investigated. In achieving the optimized coating parameters, the signal to noise (S/N) response analysis method was implemented. Confirmation tests were carried out to demonstrate the improvement using the best combination of parameters obtained from the optimization process. The surface hardness of the Ti/TiN coated and uncoated specimens was enhanced by 14% and 48%, respectively. The adhesion strength of the coating to the substrate, coefficient of friction, and surface roughness were improved by 5.1%, 43%, and 10.52%, respectively. Finally, hydroxyapatite was successfully deposited atop Ti/TiN coated Ti–6Al–4V using a PVD sputtering technique to improve the biocompatibility of the substrate. The presence of Ti/TiN interfacial thin layers between the HA layer and substrate enhanced the adhesion strength of the HA coating on the substrate by 44.57% compared to the HA-coated substrate without the interfacial layers.