Room temperature pulsed laser deposited (Ti,Al)CxN1-x coatings -: chemical, structural, mechanical and tribological properties

The aim of the present work was the improvement of titanium-aluminium nitride (TiAlN) coating by the solid-solution hardening with carbon atoms leading to titanium-aluminium carbonitride (Ti,Al)CxN1-x coatings with varying carbon (x) and nitrogen contents. The request of low deposition temperatures which are indispensable for the coating of heat-sensitive materials like tool steels of high hardness and polymers was reached by the application of the room temperature pulsed laser deposition (PLD) technique. A Nd:YAG laser of 1064 nm wavelength operated at two different laser pulse energies was used in the ablation experiments of pure TiAl targets (50 at.% Al) in various C2H2-N-2 gas mixtures. The results reveal a strong dependency of the gas mixture on the C and N content of the coatings. Furthermore, the different pulse energies change the ratio of Ti/Al atoms in the grown coatings. The crystallization was influenced too by the pulse energy and, thus, the energy and distribution of the atoms, ions and clusters. For the hardness and elastic moduli, two distinct stages in dependency on the crystallinity were found: High carbon contents lead due to the formation of pure carbon precipitations, found in the Raman investigations, to the destruction of the crystallin structure and, thus, to up to 60% lower hardnesses and elastic moduli. A low friction behaviour was found for coatings of the higher Al contents deposited at lower laser pulse energies due to the formation of carbon rich transfer layers on both the coatings and the Al2O3 counterparts. (C) 2004 Elsevier B.V. All rights reserved.