DIFFUSION BARRIER DESIGN AGAINST RAPID INTERDIFFUSION OF MCRALY AND NI-BASE MATERIAL

A physical vapour deposition, diffusion barrier coating in the system Al-O-N offers the possibility to reduce the interdiffusion between the layers of MCrAlY and the Ni-base material. The barrier function depends on the high temperature stabilization of the amorphous structure. While amorphous Al-O undergoes modification at 1100-degrees-C from several crystalline substructures up to the alpha phase, Al-O-N remains in the amorphous structure at 1100-degrees-C. This coating acts successfully as a passive diffusion barrier, and was tested up to 400 h at 1100-degrees-C in annealing tests and up to 2500 cycles in a thermal fatigue test fig with 1115-degrees-C and 200-degrees-C as the high and low peak temperatures. The gradient-free transition step achieved in the clement analysis of the depth profiles, together with the inspection of the cross-sections, confirm the excellent barrier performance.