Investigation Of Microstructure And Oxidation Resistance Of The (Ti,Al)N/TiN Coatings On The Ultra Supercritical Steam Turbine Blades

In order to improve the operation temperature and stability of the ultra supercritical steam turbine blade and prolong its service life, the (Ti,Al)N/TiN coatings were deposited on the 1Cr11MoNiW1VNbN steel by pulsed bias arc ion plating at low temperature. Isothermal oxidation tests of the (Ti,Al)N/TiN coatings were carried out at 700℃in air for 1000 hours, with the cycle oxidation tests carried out at 700℃for 200 cycles. The microstructure, mechanical property and oxidation mechanism of the coatings were studied systematically by means of SEM, EDS, XRD and microhardness tester. The study offered theoretic guidance and technical support for the protection of steam turbine blades.The (Ti,Al)N/TiN coatings were composed of TiN layer and (Tio.7Alo.3)N layer. The phase structure of the coatings was B1 type (which was also called NaCl type) with plane (200) preferred orientation. The coatings were smooth and dense as well as bonding strongly with the substrate. The results showed that the intermediate layer TiN increased the adhesion by decreasing the stress between the coatings and substrate. And the coatings showed a very high micro hardness Hv2829.8 which inferred that the coatings had great resistance to particle erosion. The results of the high temperature tests indicated that the oxide film which contained mainly TiO2 and Al2O3 on the coatings was dense after 1000 hours'oxidation at 700℃. No significant change was found on the thickness of the coatings. The macroparticle formed in deposition had no influence on the oxidation resistance of the coatings. With the processing of the oxidation, the micro hardness of the coatings fell slightly. The oxide layer of the coatings was always in compressive stress, which benefited the adhesion between the coatings and substrate. The results of cycle oxidation tests indicated that the coatings had great thermal fatigue resistance without cracks or spalling. This study showed that the (Ti,Al)N/TiN coatings had excellent comprehensive performance, the coatings could meet the project requirement of the protection of the ultra supercritical steam turbine blade.