Effect of Ar/N2 flow ratio on oxidation resistance and properties of TiAl(La)N coatings.

The TiAlN and TiAlLaN coatings were deposited on cemented carbides (YG8) and (111) silicon wafers by using a hybrid PVD coater. The composition, microstructure, mechanical properties and oxidation resistance of the coatings deposited at different nitrogen flow rates were evaluated. The concentration of titanium decreased when the N2 gas flow was increased during the deposition, and Al/Ti ratios of the coating were lower than that in the targets which is calculated to be Al/Ti=0.44. X-ray diffraction measurement showed that the lattice parameter of TiAlN coating increased from 4.22Å to 4.54Å when lanthanum is added and the position of (111) peak shifted to higher angles with the N2 flow ratio increases. Much more dense and finer grained morphology was observed when the Ar/N2 flow ratios ranged from 100/20 to 60/60. The hardness of TiAlN coating increased when lanthanum is added, while, the elastic modulus decreased at the same time. The TiAlLaN coating prepared at Ar/N2=90/30 had the maximum H/E ratio. No edge chipping was observed in the scratch track line of the coating which was deposited at the Ar/N2 flow ratio of 90/30, and it is supposed to be related to the H/E ratio. TiAlLaN coating deposited under Ar/N2=90/30 had the lowest percentage of oxidized layer, which shows the best oxidation resistance. [ABSTRACT FROM AUTHOR]