Formation of deformation bands and precipitation of Ni3Al(γ′) phase in NiAl(β)-based single crystals by thermomechanical processing

Microstructure and crystal orientation distribution of two-phase NiAl(β)/Ni3Al(γ′) alloys obtained by thermomechanical processing were investigated. Cylindrical Ni-36 and 38 at.%Al alloy single crystals with various initial loading axes were hot-compressed at a high strain rate of 1.0 s−1 and subsequently annealed in the (β/γ′) two-phase region. After the hot deformation, relatively uniform subgrain structures were formed in initial 〈111〉β-oriented crystals, while a number of deformation bands perpendicular to the compressive axis developed in 〈100〉β-, 〈110〉β- and 〈123〉β-oriented crystals. Two types of deformation bands with different crystal orientations were alternately arranged against the compressive axis. After annealing in the (β/γ′) two-phase region, a film-shaped γ′ phase with peculiar variants of the Kurdjumov–Sachs orientation relationship preferentially precipitated along the boundary between the deformation bands, resulting in the formation of a (β/γ′) two-phase lamellar structure. Formation process of the deformation bands in β phase and the crystallography of γ′ precipitates along deformation bands were discussed.