Wear and apatite growth behaviours of Zn doped diamond-like carbon coatings on β 21S Ti alloy

Zn-doped DLC coatings have been deposited on titanium 6 21S Ti alloy by a combination of plasma enhanced chemical vapor deposition (PECVD) and magnetron sputtering. The metal concentrations and thickness of the coatings have been varied by changing the parameters of the bi-polar pulsed power supply and the argon/methane gas composition. The coating thicknesses were observed to vary from 25 to 390 nm. The Zn-DLC coated titanium alloy has been characterized with FESEM, EDAX, AFM, water contact angle, Raman spectroscopy, and X-ray photoelectron spectroscopy and their nanohardness, wear resistance, and apatite growth behaviour have also been investigated. FESEM images demonstrate that with the increase in concentration of Zn, more clusters are observed which leads to roughening of the coatings. The variation of VI, ratio with Zn concentration has been obtained from Raman spectroscopy studies. The hardness of the coating with 210 nm thickness is 14.8 ± 2.5 GPa and Young's modulus is 377 ± 49.8 GPa. Water contact angle measurements show that with increase in Zn concentration coatings are turned to be hydrophobic in nature. A low coefficient of friction of 0.1-0.2 at 5 N load was observed from reciprocating wear studies in the coated substrate compared to uncoated substrate indicating better wear resistance behaviour of the Zn-DLC coated substrate. EDS and XPS studies show the formation of calcium phosphate phase over Zn-DLC coated substrate confirming the apatite growth. (author)