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

Abstract 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 N 2 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 4.22 A to 4.54 A when lanthanum is added and the position of (111) peak shifted to higher angles with the N 2 flow ratio increases. Much more dense and finer grained morphology was observed when the Ar/N 2 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/N 2  = 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/N 2 flow ratio of 90/30, and it is supposed to be related to the H/E ratio. TiAlLaN coating deposited under Ar/N 2  = 90/30 had the lowest percentage of oxidized layer, which shows the best oxidation resistance.