TiN-Ag as an antimicrobial and wear resistant coating

Nosocomial infections are a major clinical concern, posing great risks for patients and rising costs for health services providers. This work aims at developing a hard, wear resistant coating, whose antimicrobial properties shall prevent the transmission of infections. TiN coatings deposited by Physical Vapour Deposition, PVD, with different Ag contents have been studied, especially in relation to the hardness and adhesion, their microstructure and morphology. The antimicrobial activity of the surfaces has been assessed against Staphylococcus epidermidis at different time frames, one of the most troublesome source of infections in trauma and orthopaedic surgeries. The electro-tribology properties of different silver contest have been studied. Finally, the coatings have been deposited on surgical acetabular reamers and wear resistance tests have been carried out against synthetic composite bone (simulating cortical and cancellous bone). Results have shown a good coating adhesion on stainless steel (both quantitatively in the scratch tests and qualitatively in the tests against synthetic composite bone), while the hardness decreased with higher Ag percentages. Furthermore, coatings exhibited antimicrobial activity against S.epidermidis, limited silver release, a remarkable wear resistance (vs. uncoated surgical acetabular reamers), while the electrical contact resistance provided valuable information about the evolution of friction and the status of the coating. Therefore TiN-Ag coatings present promising features for reducing the risk of infections, monitoring and extending cutting edge life and quality, and thus limiting damage to living tissues, e.g. necrosis.This work was supported by the Economic Development Agency of the Basque Government under the following grants: Elkartek program, project Frontiers-V ref. KK-2019/00077 and BACTERICOAT project N. EXPT IG-2006/0000465, IT-2007/0000623, IT-2008/0000488

Facilitating TiB2 for filtered vacuum cathodic arc evaporation

TiB2 is well established as a superhard coating with a high melting point and a low coefficient of friction. The brittle nature of borides means they cannot be utilised with arc evaporation, which is commonly used for the synthesis of hard coatings as it provides a high deposition rate, fully ionised plasma and good adhesion. In this work, TiB2 conical cathodes with non-standard sintering additives (carbon and TiSi2) were produced, and the properties of the base material, such as grain structure, hardness, electrical resistivity and composition, were compared to those of monolithic TiB2. The dependence of the produced cathodes’ electrical resistivity on temperature was evaluated in a furnace with an argon atmosphere. Their arc–evaporation suitability was assessed in terms of arc mobility and stability by visual inspection and by measurements of plasma electrical potential. In addition, shaping the cathode into a cone allowed investigation of the influence of an axial magnetic field on the arc spot. The produced cathodes have a bulk hardness of 23–24 GPa. It has been found that adding 1 wt% of C ensured exceptional arc-spot stability and mobility, and requires lower arc current compared to monolithic TiB2. However, poor cathode utilization has been achieved due to the steady generation of cathode flakes. The TiB2 cathode containing 5 wt% of TiSi2 provided the best balance between arc-spot behaviour and cathode utilisation. Preventing cathode overheating has been identified as a main factor to allow high deposition rate (±1.2 µm/h) from TiB2-C and TiB2-TiSi2 cathodes

Comprehensive microstructural and optical characterization of the thermal stability of aluminum‑titanium oxynitride thin films after high temperature annealing in air

The thermal stability of two AlyTi1- y(OxN1-x) layers prepared by cathodic vacuum arc deposition with different oxygen content was studied after high temperature annealing of the samples in air. These layers were designed to be part of solar-selective coating (SSC) stacks. Compositional and microstructural characterization of the thin films was performed before and after the thermal treatment by elastic recoil detection (ERD), transmission electron microscopy, and Raman spectroscopy. AlyTi1- yN sample was stable after 2 h of annealing at 450 °C. Initial stages of the formation of a surface oxide layer after annealing at 650 °C were observed both by ERD and Raman analysis. Contrarily, no changes were found after 2 h annealing treatment either at 450 and 650 °C in the composition and microstructure of AlyTi1- y(OxN1-x) sample. In both samples, the formation of a surface anatase TiO2 film was reported after 2 h annealing at 800 °C. These compositional and microstructural changes were correlated with the optical properties determined by spectroscopic ellipsometry. A transition from metallic to dielectric behavior with increasing annealing temperature was observed. These results complete the durability studies on the designed SSC based on AlyTi1- y(OxN1-x) materials, confirming that these stacks withstand breakdown at 600 °C in air.H2020 RISE project “Framework of Innovation for Engineering of New Durable Solar Surfaces GA-645725Spanish Ministry of Science and Innovation project “Recubrimientos innovadores preparados por magnetron sputtering para absorción solar selectiva" PID2019-104256RB-I00Agencia Estatal de Investigacion (AEI) project “Entrenamiento avanzado en materiales para superficies solares duraderas EIN2020-112163 /AEI/10.13039/50110001103

Design of high-temperature solar-selective coatings based on aluminium titanium oxynitrides AlyTi1−y(OxN1−x). Part 1: Advanced microstructural characterization and optical simulation

Aluminium titanium oxynitrides were studied as candidate materials for high temperature absorbers in solar selective coatings due to their excellent stability and their tuneable optical behaviour. A set of individual AlyTi1−y(OxN1−x) layers with different oxygen content was prepared by cathodic vacuum arc (CVA) deposition. The composition, morphology, phase structure and microstructure of the films were characterized by elastic recoil detection (ERD), scanning and transmission electron microscopy and X-ray diffraction. An fcc phase structure is found in a broad compositional range of AlyTi1−y(OxN1−x). Simultaneously, sample microstructure and morphology undergo systematic changes from a columnar growth to the development of a heterogeneous structure with spherical nanoparticle inclusions when the oxygen concentration is increased. The optical properties were determined by spectroscopic ellipsometry and UV–Vis–NIR and FTIR spectrophotometry. A comprehensive analysis of the film properties allowed an accurate modelling of the optical constants of the AlyTi1−y(OxN1−x) in the whole wavelength range of solar interest (from 190 nm to 25 µm). It points to a transition from metallic to dielectric behaviour with increasing oxygen content. Consequently, it is demonstrated that the optical properties of these AlyTi1−y(OxN1−x) deposited films can be controlled in a wide range from metallic to dielectric character by adjusting the oxygen concentration, opening a huge range of possibilities for the design of solar selective coatings (SSC) based on this material. Complete SSC, including a TiN layer as IR reflector, were designed by applying optical simulations, obtaining excellent optical selective properties of α = 94.0% and εRT = 4.8%