High temperature oxidation behaviour of mono-layer and bi-layer coatings

In the current work, the mono-layer Al–Cr–Ni coating and the bi-layer Al–Ni/Al–Cr coating were successfully synthesised on the Ti–6Al–4V alloy substrate by mechanical alloying. The effect of powder ratio was studied. The microstructure and phase composition of the two coatings were investigated. The mono-layer coating was composed of grey black composite structure. In the bi-layer coating, the Al–Cr outer layer exhibited a composite structure similar to the Al–Cr–Ni coating. The results showed the approximate thickness of Al–Cr–Ni coating was 140 μm, while that of bi-layer coating was more than 200 μm. Both coatings were well bonded to the substrate. After 850°C of cyclic oxidation for 100 h, cracks only occurred at the interface of the mono-layer coating, and no significant defects were found at the two interfaces of the bi-layer coating. The cyclic oxidation test results showed the bi-layer coatings exhibited more excellent oxidation resistance.