MODIFICATIONS PRODUCED BY GERMANIUM IN MO SI2 COATINGS ON MOLYBDENUM

Molydenum disilicide coatings can afford a good protection against H.T . oxidation to molybdenum substrates. Their main use limitation is the ir sensitivity to thermal cycling, due to the mismatch between expansi on coefficients of silica and the intermetallic substrate and to inter diffusion between coating and molybdenum substrate which leads to Mo5S i3 formation, a compound very sensitive to H.T. oxidation. Alloying of MoSi2 with germanium can have a beneficial influence from these two p oints of view. Germanium increases the resistance of the silica protec tive film to thermal cycling; it also lowers the diffusion rate in the MoSi2/Mo system.