Some relevant issues related to the use of amorphous diamond coatings for medical applications

Amorphous diamond (AD) films (sp(3) bonding fraction 80%, thickness 200-1000 nm) have been deposited on CoCrMo alloy stainless steel AISI316 L, AISI420. Ti6Al4V alloy and alumina test samples and hip and knee joints using pulsed plasma accelerator method. By using high-energy plasma beams and proper intermediate layers, AD coatings with a high adhesion were produced. We have shown that these coatings are biocompatible, causing no local tissue reactions and offer good tribological characteristics, e.g. against ultra-high molecular weight polyethylene (UHMWPE). In this study, we concentrate on three relevant issues related to the applicability of AD coatings: (a) high adhesion of the coating to the implant surface and high quality, (b) high-quality surface finish and (c) good corrosion resistance in biological fluids. It should be emphasised that the tribochemical conditions, e.g. in a hip joint, are very severe, and even the best materials (CoCrMo alloys) used at the moment are dissolved or worn out at least 0.02-0.06 mm in 10 years (mean linear wear rate). The results show that in all the combinations studied, AD coating was able to improve the wear and corrosion resistance compared to the uncoated materials, In the best cases, the wear rate was decreased by a factor of 30-600. However, typically special procedures such as sputtering, high deposition energies, filtering of plasma beam, intermediate layers or laminated structures were necessary to optimise the performance. (C) 1998 Elsevier Science S.A.