Effects of Ti_(0.5)Al_(0.5)N coatings on the protecting against oxidation for titanium alloys

Ti_(0.5)Al_(0.5)N coatings were deposited on TC11 (Ti-6.5Al-3.5Mo-1 .5Zr-0.3Si) and silicon substrates using a cathode arc ion-plating system. The microstructure, composition, phase structure, and oxidation-resistance of the alloys and nitride coatings were investigated by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, Auger electron spectroscopy, and thermal analyzer. The results show that the oxidation resistance of the titanium alloy is relatively limited; the compound structures of Ti mixed with A1 oxides are formed during the heating process. The phases of the Ti_(0.5)Al_(0.5)N coatings are composed of a TiN solid solution phase. The oxidation kinetics obeys the parabolic law. During the oxidation process, the selective oxidation of Al occurs, thus protecting the underlying coating and substrate.