On the mechanism of secondary reaction zone formation in a coated nickel-based single-crystal superalloy containing ruthenium

The secondary reaction zone (SRZ) formation at the interface between CoNiCrAlY coating and experimental Ni-based single-crystal superalloy substrate with 1 wt.% Ru has been investigated. The γ′ grains nucleated epitaxially with grains in coated layer. Preferential formation of the SRZ was observed along the 〈1 1 0〉 directions. The factors affecting the SRZ kinetics are discussed in terms of the preferential dislocation gliding direction where recrystallization would be most active due to high strain energy and the supply of fast interdiffusion pathways.