Laser induced chemical vapour deposition of TiN coatings at atmospheric pressure

Abstract
Laser induced Chemical Vapour Deposition of a wide variety of materials has been studied extensively at reduced pressures. However, for this technique to be economically and industrially applicable, processes at atmospheric pressure are preferred. A model study was made on the substrate-coating system molybdenum-titaniumnitride focussing on the feasibility to deposit TiN films locally at atmospheric pressure. The results of this study turned out to be very promising. A Nd-YAG laser beam ([MATH] = 1064 nm), directed perpendicular to the substrate, is used to locally heat the substrate (pyrolytic atmospheric pressure Laser induced Chemical Vapour Deposition). The reactive atmosphere consists of TiCl₄, N₂ and H₂. The Laser Chemical Vapour Deposited nitride coating is characterized by SEM, EDAX, XRD, XPS, SAM and microhardness tests. The results show that the coatings are pure, polycrystalline, stoichiometric TiN with a hardness in the range 1900 to 2300 HV. The influence of laser irradiation parameters on the temperature distribution induced in molybdenum and on the deposit shape, spatial distribution and microstructure of TiN films has been studied. A fast laser spot pyrometer was built for the in-situ temperature measurements. Depending on the deposition conditions, different types of profiles, microstructures and distribution widths are observed. Two examples of atmospheric pressure Laser CVD deposited TiN films on 3D-objects are given.