Titanium Aluminum Nitride Coatings Research Articles

Electrochemical characteristics of steel coated with TiN and TiAlN coatings

The corrosion protection characteristics of titanium nitride (TiN) and titanium–aluminum nitride (TiAlN) coatings produced on cemented carbon steel targets were investigated in aqueous sodium chloride solution. All coatings were produced by cathodic arc plasma deposition. The results indicated that it was possible to follow the corrosion behavior of the coated systems over a period of 300–900 h of immersion. It was found that the TiN and TiAlN coatings had a lower corrosion rate (current density), about three orders of magnitude lower than the untreated steel substrates. The metal substrate was actually passive in these experimental conditions, and exhibited an electrochemical impedance response that could be described by means of the same equivalent circuit than for the coating. Nevertheless, the analysis of the impedance parameters allowed for direct information concerning the enhancement of the corrosion resistance of the coated system as compared to the passive uncoated metal substrate to be extracted. The major corrosion mechanism for the coated samples arises from electrolyte penetration in the pores of the deposits, which may eventually lead to the development of localized forms of corrosion.

Titanium–aluminum–nitride coatings for satellite temperature control

Intense solar irradiation, radiative cooling to outer space, and internal heat generation determine the equilibrium temperature of a spacecraft. The balance between the solar absorption and thermal emittance of the surface is therefore crucial, in particular for autonomous parts directly exposed to the solar radiation and thermally insulated from the main thermal mass of the spacecraft. The material composition but also the coating thickness are found to influence the equilibrium temperature of an object in space. In this paper we report on a systematic search for a suitable composition and thickness of Ti x Al y N z alloy coatings prepared by reactive, unbalanced magnetron sputtering from targets consisting of differently sized titanium and aluminum sectors. The films were deposited on glass, glassy carbon, aluminum sheet metal, and on sputtered aluminum and Ti x Al (1− x) films on glass. The stoichiometry and sheet resistance of the films was determined with Rutherford backscattering and four-point probe measurements respectively. Reflectance spectra for the visible and infrared spectral ranges were used to obtain average solar absorptance and thermal emittance values used in model calculations of the equilibrium temperature. Neglecting internal heat contributions, the lowest calculated equilibrium temperature in orbit around the Earth, 32.5°C, was obtained for a 505-nm-thick Ti 0.14Al 0.47N 0.40-film.

Thermodynamic Modeling of the Ti-Al-N System and Application to the Simulation of CVD Processes of the (Ti,Al)N Metastable Phase

Owing to its numerous technological applications in the fields of integrated circuits and protective coatings, the TiAlN system has aroused increasing interest. The purpose of this paper is to propose a thermodynamic model and simulate its processing conditions. The calculation and optimization of the TiAlN ternary phase diagram was performed as the first step to modeling two competitive CVD processes used for the processing of titanium aluminum nitride coatings: low pressure chemical vapor deposition (LPCVD) and metal-organic chemical vapor deposition (MOCVD). Thermodynamic simulations of the processes have been used to investigate the effect of varying operating parameters and to predict the nature of the phases present at equilibrium. Calculations were then made on the TiAlNClHAr and TiAlNCHAr chemical systems, corresponding to the two CVD processes.

The mechanical and tribological properties of titanium aluminium nitride coatings formed in a four magnetron closed-field sputtering system

Titanium aluminium nitride coatings have been deposited onto rotating tool steel substrates of three different roughnesses using four unbalanced rectangular planar magnetrons arranged in a closed field configuration. Three of the magnetrons were fitted with titanium targets and the fourth with aluminium. By varying the magnetron powers and the speed of substrate rotation, coatings of chosen composition can be deposited as either multilayers or homogeneous alloys. The composition and morphology of the films have been investigated using X-ray diffraction and scanning electron microscopy, and their mechanical properties have been characterised by scratch testing and microhardness measurement. The tribological properties have been established by pin on disc testing against hemispherical tungsten carbide pins, using relocation profilometry to provide accurate measurements of wear depths less than the original surface roughness. Good correlation of the mechanical and tribological properties is reported.

Tribological characterisation of hard carbon films produced by the pulsed vacuum arc discharge method

Hard diamond-like carbon (DLC) films were deposited on silicon and high-speed steel substrates using a pulsed vacuum arc discharge method. The plasma plume was focused on the substrate using a direct electromagnetic coil. Several methods were used for coating characterisation. The film composition was analysed using Rutherford backscattering spectroscopy and forward recoil spectroscopy. About 0.5 at.% oxygen and about 1 at.% hydrogen was detected in the film. The tribological properties of the carbon films were studied using pin-on-disc tests. The counterface materials employed were alumina and hardened steel (AISI 52100 and M50) pins, which were slid against the coated substrates. The friction coefficient was measured and the wear surfaces were studied. The sliding speed was in the range 0.02–0.6 m/s and the load in the range 5–20 N. The tests were carried out in air with a relative humidity of 50±2% and at a temperature of 24±3 °C. The test results show that the DLC coatings produced for this study generally had a coefficient of friction (μ) of about 0.2. The lowest value measured was μ=0.14. The wear resistance of the coatings was good, provided that the adhesion to the substrate was sufficient. The comparative tests with titanium nitride and titanium aluminium nitride coatings showed that DLC films are considerably more wear resistant than titanium-based coatings.