DIFFUSION BARRIER COATINGS WITH ACTIVE BONDING, DESIGNED FOR GAS-TURBINE BLADES

A physical vapour deposition diffusion barrier coating, based on amorphous alumina, offers the possibility to reduce the interdiffusion between the MCrAlY overlay and the Ni-base material occurring at elevated temperatures. The barrier function depends on the high temperature stabilization of the dense, amorphous structure. The coating contains nitrogen against the crystallization of alumina phases. Owing to the fact that todays MCrAlYs need diffusion bonding for a satisfactory adhesion, the barrier is deposited as X-Al-O-N, with X as a reactive element forming a diffusion bond layer with the Ni-base and MCrAlY during the first thermal treatment. The paper reviews several high temperature tests in which the barrier function of the alumina based coating was proved. The bonding effect of the chosen X element is explained. The influence of a deposition parameter variation on the formation of the reactive bonding zone is investigated. With this diffusion barrier, the temperature level of the first stage turbine blade could be increased up to 1100 degrees C in the MCrAlY-Ni-base interface.