Corrosion behaviour and adhesion properties of sputtered tantalum coating on Ti6Al4V substrate
Tantalum coating on Ti6Al4V substrate was prepared by sputtering and the mechanical and corrosion performance of the tantalum coating was investigated. In addition to the normal structure of a sole tantalum film on the substrate, a buffer layer of titanium was first deposited on the substrate in a hope to improve the film adhesion. XRD examination shows that the Ta coatings exhibit a α/β dual-phase structure. Both the sole Ta coating and the Ta coating with a Ti buffer layer increased the apparent hardness of the surface of the Ti6Al4V substrate significantly. The compressive residual stress of the Ta/Ti of the order of 0.9 GPa is noticeably reduced comparing to 1.2 GPa of the sole Ta coating, resulting in an improved adhesion between the coating-substrate interface. The hydrophobicity of the Ti6Al4V surface after Ta coating also increased, which is believed to help in protein absorption and enhance lubrication. The corrosion current density of the Ta coated Ti6Al4V decreased from 2.0 x 10− 8 to 3.4 x 10− 9 A·cm− 2 (at high scan rates) comparing to the uncoated Ti6Al4V substrate. The mechanisms of the improved corrosion current density by the Ta coating and the enhancement of mechanical bonding of the Ta coating by a Ti buffer layer are further discussed.