The effect of structure and chemistry on the strength of FeCrAl(Y)/sapphire interfaces: I. Structure and chemistry of interfaces

FeCrAl/Al2O3 and FeCrAlY/Al2O3 interfaces were formed by sputter deposition of alloy thin films on A-plane sapphire substrates. The microstructure of both Y-containing and Y-free films consisted of single-phase BCC columnar grains of fairly uniform composition across the film thickness. Both films exhibited a high degree of 〈110〉 texture along the growth direction normal to the interface with no preferred in-plane orientation. In both cases, a thin amorphous layer was observed at the interface in the as-deposited state. Annealing the films for 16 h at 850 °C improved the crystalline quality of the film/substrate interface and led to grain growth within the films. The annealing did not lead to any significant changes in the film composition in the Y-free film. In the Y-containing film, yttrium oxide precipitates formed in the near interface region, depleting the adjacent alloy matrix of Y completely; accompanied by a significant enhancement of Al in the film, very close to the interface.