Diamond like carbon (DLC) coatings have been proven to be an excellent choice for wear reduction in many technical applications. However, for successful adaption to the orthopaedic field, layer performance, stability and adhesion in physiologically relevant setups are crucial and not consistently investigated. In vitro wear testing as well as adequate corrosion tests of interfaces and interlayers are of great importance to verify the long term stability of DLC coated load bearing implants in the human body. DLC coatings were deposited on articulating lumbar spinal disks made of CoCr28Mo6 biomedical implant alloy using a plasma-activated chemical vapor deposition (PACVD) process. As an adhesion promoting interlayer, tantalum films were deposited by magnetron sputtering. Wear tests of coated and uncoated implants were performed in physiological solution up to a maximum of 101 million articulation cycles with an amplitude of ±2° and −3/+6° in successive intervals at a preload of 1200 N. The implants were characterized by gravimetry, inductively coupled plasma optical emission spectrometry (ICP-OES) and cross section scanning electron microscopy (SEM) analysis. It is shown that DLC coated surfaces with uncontaminated tantalum interlayers perform very well and no corrosive or mechanical failure could be observed. This also holds true in tests featuring overload and third-body wear by cortical bone chips present in the bearing pairs. Regarding the interlayer tolerance towards interlayer contamination (oxygen), limits for initiation of potential failure modes were established. It was found that mechanical failure is the most critical aspect and this mode is hypothetically linked to the α-β tantalum phase switch induced by increasing oxygen levels as observed by X-ray diffraction (XRD). It is concluded that DLC coatings are a feasible candidate for near zero wear articulations on implants, potentially even surpassing the performance of ceramic vs. ceramic.

Ternary transition metal nitride coatings are promising for many applications as they can offer improved hardness and oxidation resistance compared to binary counterparts. A common challenge in the deposition of functional nitride thin films is oxygen contamination. Even low amounts of oxygen contamination can adversely affect the functional properties of the thin films. Here, we present a practical approach for the growth of virtually oxygen-free (Ti, Zr)N thin films. To cover the complete compositional range of (Ti,Zr)N coatings we employ combinatorial reactive co-sputtering. The depositions are carried out with or without applying a low-power radio-frequency (RF) bias voltage to the substrate holder to study the possibility of decelerating energetic oxygen ions and effectively reducing oxygen contamination in the growing film. High-throughput structural analysis and functional property mapping are used to elucidate the synthesis-property relationships. The structural analysis indicates solid solution formation over the entire compositional range, as evidenced by Vegardian lattice scaling, regardless of the applied RF substrate bias. Irrespective of the composition of the films, the application of RF substrate bias leads to a dramatic reduction of oxygen contamination, as demonstrated by X-ray photoelectron spectroscopy (XPS) depth-profile mapping. This is reflected in a significant improvement in the films' conductivity and hardness. We demonstrate that the reduction in oxygen contamination is intrinsic to the process and not due to changes in the microstructure. The approach presented here is applicable to both conductive and insulating substrates and provides a practical route to synthesize nitride thin films with improved purity that can be applied in standard sputter chambers and on many different material systems.