Abstract: Three kinds of aluminide coatings were fabricated by chemical vapor deposition（CVD）on the surface of the nickel-based superalloy substrates at the deposition pressure of 150, 200 and 250 mbar, respectively. The effect of deposition pressure on phase structure and high temperature oxidation behavior of the specimens with aluminide coating was systematically investigated. The phase structure, surface morphology and elemental composition of the three kinds of aluminide coatings were analyzed by XRD, SEM and EDS. The results indicate that the phase constituents of three kinds of aluminide coatings are detected to be β-NiAl. Two phases including of Ni_1.04Al_0.96 and Ni_1.1Al_0.9 are gained in the coating specimens prepared at the deposition pressure of 200 mbar. After the isothermal oxidation at 1100℃ for different dwelling times, the main phase β-NiAl transforms into γ′-Ni₃Al with formation of Al₂O₃. Differently, the peak intensity of γ′-Ni₃Al phase is the weakest for the specimens deposited at the pressure of 250 mbar. The oxidative weight gain rate of the three aluminide coatings is 0.037, 0.022 and 0.018g/（m²·h）, respectively. The oxidation weight gain of the coating specimens at the deposition pressure of 150 mbar is correspondingly larger than that of the other two coating specimens. The lower deposition pressure is, the more micropores on the surface of the coating exist,and the more easily microcracks appear on the thin film of the coating surface and further form into the spllation of oxide scale after high temperature oxidation. Based on the experimental results, the coating specimens prepared at deposition pressure of 250 mbar show the best surface microstructure,elemental content and high temperature oxidation resistance.

Key words: chemical vapor deposition, aluminide coating, deposition pressure, phase structure, high-temperature oxidation