Comparison of oxidation resistance of Al–Ti and Al–Ni intermetallic formed in situ by thermal spraying

A pure Al coating and an Al/Ni composite coating were deposited on the surface of a pure Ti substrate by thermal spraying. To enable the in situ reaction between the coatings and the substrate, the specimens were heated to 800 °C. Furthermore, the high-temperature oxidation resistance and the protection mechanism of the Ti–Al and Ni–Al intermetallic compounds were compared. The results showed that after heating to 800 °C, the diffusion region of the Al/Ti specimen mainly comprised the TiAl₃ phase, and the thickness of the diffusion region first increased and then decreased as the reaction time was extended. The diffusion region of the Al/Ni/Ti specimen consisted of the Ni₂Al₃ and NiAl phases after heating to 800 °C, and the thickness of the Al/Ni diffusion layer showed parabolic growth as the reaction time was extended. After the oxidation treatment (800 °C for 100 h), oxygen diffused not only into the Al/Ti diffusion region, but also into the Ti substrate. For the NiAl intermetallic coating, no elemental Ti was found on the surface of the specimen and no oxygen was found in the Ti substrate after the oxidation treatment. The NiAl intermetallic coating had better oxidation resistance than the TiAl₃ intermetallic coating. (paper)