Over the last 20 years Ti_1-xAl_xN coatings were the domain of PVD.

Published in 2008 the first cubic Ti_1-xAl_xN coatings containing high Al (x>0.8) were developed in a lab scale CVD system. Remarkable wear behavior and properties were reported. In 2011 a tool manufacturer succeeded to develop an in house CVD process to produce CVD Ti_1-xAl_xN coated inserts. They reported high Al-content (>70%), high hardness, a phase mixture of cubic and hexagonal and excellent cutting results.

We now report on Ti_1-xAl_xN results achieved with the first commercially available CVD systems SCT600 and SCT400 which can coat up to 15’000, respectively 8’000 pcs. ½”inserts per batch . The newly developed NH₃ module proved its capability to coat homogenously single phased cubic Ti_1-xAl_xN in medium temperatures and Al contents >70%. By varying the gas parameters phases of the Ti_1-xAl_xN coatings could be tailored (pure cubic, mixed cubic and hexagonal) while keeping the Al-content high. The coated samples were characterized in terms of structure, composition, physical and mechanical properties.

There is a significant need within a variety of applications for surfaces that exhibit and maintain high hydrophobicity, oleophobicity and good wear resistance with a corresponding low coefficient of friction after exposure to environments of high thermal stress in oxidative environments. Examples include areas such as fuel delivery and exhaust systems, and heat transfer systems. With modifications of a commercially available CVD process, a new material is being evaluated for the above characteristics, before and after exposure to 450°C in air. A variety of surface evaluation methods will be discussed, including the use of tensiometer and goniometer data for contact angle analysis, surface FT-IR microscopy and X-ray photoelectron spectroscopy for material composition analysis, potentiometric information for electrochemical and corrosion resistance analysis, and pin-on-disc data for wear resistance and friction coefficient evaluation. The method of deposition will also be discussed, as it allows for the deposition on to complex three-dimensional configurations, in bulk quantities, and on to parts of significant size.

A material that has proven useful in the harsh environment of metal cutting is aluminium oxide. Aluminum oxide shows great properties in wear resistance, toughness and deformation resistance at high temperatures. The most common phases of aluminium oxide usually obtained in the CVD process are α-Al2O3 and κ-Al2O3. The thermodynamically stable phase is α-Al2O3. If a cutting tool is coated with κ-Al2O3 the film may undergo phase transformation during the cutting process which could reduce the durability of the tool coating and therefore α-Al2O3 is the desired phase. Aluminum oxide is usually combined with layers of titanium carbonitrides. Ti(C,N) which has complementary wear properties to aluminum oxide making it widely used on metal cutting tools. It has proven to be a difficult task to deposit α-Al2O3 on Ti(C,N) with CVD as the phase obtained is mainly κ-Al2O3.

In this investigation phase selective growth of α-Al2O3 is demonstrated by thin interlayers of TiO2 deposited by atomic layer deposition.

Many studies attempted to optimize epitaxial growth of AlN on sapphire c-plane using AlCl3 and NH3 as precursors. The most promising way is to protect the sapphire surface with a controlled nucleation/nitridation layer grown at low temperature (below 1200°C) and low growth rate [1] prior the deposition at high temperature (typically 1500°C). Another solution is to control precisely the N/Al ratio in the gas phase during growth. Previous studies [2] concluded that the optimal N/Al ratio in gas phase for AlN epitaxial growth on various substrates was about 1.5. The main issue is that in all previous experiments, the N/Al ratio influence was investigated whereas growth rate and layer thickness also varied.

On the other hand, kinetic modeling of AlN growth rate is available [3], so that a study of the influence of N/Al ratio at constant thickness and constant growth rate is possible without any time-consuming growth rate calibration experiments. This study focuses on the influence of the N/Al ratio in gas phase at constant growth rate and thickness. The influence of layer thickness at constant growth rate and layer growth rate at constant thickness is also discussed. Finally, the addition of a protective by different ways (two steps growth or continuous growth) is studied.

This study leads to the synthesis of 5 µm AlN templates grown at 5 µm/h with a crystalline quality of 460 arcsec for the FWHM 0002 reflectivity, exhibiting no cracks on two inches sapphire wafers. The photoluminescence spectra and TEM interface image of some samples are also presented.

[1] M. Balaji, A. Claudel, V. Fellmann, I. Gélard, E. Blanquet, R. Boichot, A. Pierret, B. Attal-Trétout, A. Crisci, S. Coindeau, H. Roussel, D. Pique, K. Baskar, M. Pons, Journal of Alloys and Compounds 526 (2012) 103.

[2] A. Claudel, E. Blanquet, D. Chaussende, R. Boichot, B. Doisneau, G. Berthomé, A. Crisci, H. Mank, C. Moisson, D. Pique, M. Pons, Journal of Crystal Growth 335 (2011) 17.

[3] R. Boichot, A. Claudel, N. Baccar, A. Millet, E. Blanquet, M. Pons, Surface and coatings Technology, 205 (2010) 1294.