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DAAD-PPP-PROCOL_57394123 Self-lubricant and bactericidal TiAlN(Ag)

PPP-PROCOL_57394123_Logo

Projektbearbeiter: Diego Grisales Pareja

Surgical and dental instrumentation is usually manufactured with martensitic stain-less steel such as AISI 420 and AISI 440. These steels are common in this industry due to their biocompatibility and high hardness after heat treatment processes, ap-proximately 50 HRC. However, corrosion and wear phenomena lead to the reduction of tools life span. These phenomena occur on surgical instrumentation, not only due to usage in medical treatments but also during sterilisation processes in auto-claves and acid solutions. Different surface pre-treatments have been used in order to improve the performance and durability of these instruments. Among them, plas-ma nitriding and the deposition of hard nitrides, such as ZrN, TiN, TaN and TiAlN, are worth highlighting. Protective coatings are deposited by different techniques like chemical vapour deposition CVD, Arc-PVD, Direct Current Magnetron Sputtering DCMS, Plasma Assited phisycal vapour deposition PACVD and recently gaining ground, High Power Impulse Magnetron Sputtering process HiPIMS. Nitride coat-ings present a relatively high hardness (20 – 35 GPa), high corrosion resistance and low friction coefficient. One of the problems to overcome in the manufacturing of surgical and dental instrumentation is the possibility of the infection of patients due to the utilisation of contaminated instruments in surgical rooms, dental centres and recovery rooms. In the search for a solution to bacteria contamination problem, sev-eral authors have proposed the addition of silver, a proved antibacterial metal, to the surface of the instruments.

During this project, the deposition of the hard coating TiAlN coatings doped with Ag nanoparticles by means of DCMS and HiPIMS is proposed. Although TiAlN is a hard and wear resistance material, the addition of soft and ductile Ag into the structure could act negatively in the properties of the compound material. Silver has almost not solubility in TiAlN and has no affinity to nitrogen, allowing the deposition of me-tallic nanoparticles distributed in the ceramic matrix. Consequently, the amount, dis-tribution, density and size of the Ag nanoparticles are of vital importance in the bac-tericide and structural behaviour of the TiAlN(Ag) coating. Additionally, a post depo-sition heat treatment is necessary to guarantee the availability of silver on the sur-face of the instrument and promote the bactericidal effect. This as consequence of the diffusion of the silver nanoparticles throughout the coating imperfections and limits of grain creating nanowires that act as a dispenser of silver.

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Figure 1: (a) Positioning of nanoparticles of Ag in between the columns and voids of the TiAlN matrix; (b) Nanowires of Ag originated after a post treatment or during service.

However, the optimisation of the bactericidal effect and tribomechanical properties of the TiAlN(Ag) coatings cannot act in detriment of the corrosion resistance of these. For this reason, it is necessary to control and evaluate the electrochemical behav-iour of the coating systems developed in this project. The main objective of this pro-ject is to Develop a nanocomposite coating of TiAlN(Ag) that possess high hardness and excellent wear and corrosion resistance, all these combined with an appropriate bactericidal effect, for the purpose of further applications on surgical and dental in-strumentation.

PPP-PROCOL_57394123_Abbildung_2

Figure 2:TiAlN coating deposited by hybrid (DCMS/HiPIMS) technology doped with 25 at.% Ag at room temperature (left) and after heat treatment at 200 and 400°C.