Control of microstructure and orientation distribution in Ni–Al-based ( β/ γ′) two phase alloys by thermomechanical processing

Abstract

Microstructure and orientation distribution of two phase Ni–Al( β)/Ni 3Al( γ′) alloys obtained by thermomechanical processing were examined using electron back-scatter diffraction pattern technique. Cylindrical specimens were hot-compressed in the β phase region and subsequently annealed in the ( β/ γ′) two phase region. After the hot deformation, equiaxed β grains surrounded by high angle boundaries were homogeneously formed due to dynamic recrystallisation under adequate condition. Moreover, strong 〈1 1 1〉 fibre texture parallel to the compressive axis developed in the β phase because of the lattice rotation during hot deformation. After annealing in the two phase region, γ′ phase transformed from β phase with 〈1 1 1〉 β fibre texture satisfying the Kurdjumov–Sachs relationship and resulting in the formation of 〈1 1 0〉 γ′ fibre texture. Film-shaped γ′ phase preferentially often precipitated along the β grain boundaries and a large number of ( β/ γ′) boundaries were partially coherent. This thermomechanical processing was effective in controlling the crystallography of γ′ along the β grain boundaries.