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

A physical vapour deposition diffusion barrier coating, based on amorp hous alumina, offers the possibility to reduce the interdiffusion betw een the MCrAlY overlay and the Ni-base material occurring at elevated temperatures. The barrier function depends on the high temperature sta bilization of the dense, amorphous structure. The coating contains nit rogen against the crystallization of alumina phases. Owing to the fact that todays MCrAlYs need diffusion bonding for a satisfactory adhesio n, 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 te sts in which the barrier function of the alumina based coating was pro ved. The bonding effect of the chosen X element is explained. The infl uence of a deposition parameter variation on the formation of the reac tive bonding zone is investigated. With this diffusion barrier, the te mperature level of the first stage turbine blade could be increased up to 1100 degrees C in the MCrAlY-Ni-base interface.