Abstract: A multi-component diffusion coating has been developed to protect Mo-based alloysfrom high temperature environmental attack. Aluminum addition was made duringthe coating process to improve the oxidation resistance by developing hexagonal Mo(Si,Al)2 through the development of the halide activated pack cementation coating processon pure Mo substrate. The results show that Mo(Si, Al)2 formed as a main phase onthe surface and a little amount of Mo5Si3 also formed. The total thickness of coatingis tens of μm at 1373K. During the cyclic oxidation test at high temperature(at about1323K in air), mullite (3Al2O3@2SiO2) and some SiO2 formed. The addition of Alis beneficial for MoSi2 coating and the Al-doped coating exhibited only a small weightgain and protected the Mo substrate, while the MoSi2 coating without Al suffered asignificant weight loss, indicating a loss of volatile MoOs after cycles.

Key words: multi-component coating, Mo(Si, Al)2, halide activated pack ce-mentation,