A high-resolution-electron-microscopy study of a γ/γ′-α directionally solidified eutectic alloy - Part I The as-solidified state

The microstructure of a γ/γ′-α directionally solidified (DS) eutectic alloy with a nominal composition of Ni-30.26Mo-6.08Al-1.43V (wt%) was investigated by means of high-resolution electron microscopy (HREM) and analytical electron microscopy. The α-fibres exhibited a typical morphology with a rectangular cross-section and they displayed the Bain orientation relationship (OR) with the γ′/γ matrix; that is, [001]α∥[001]γ′ and (110)α∥(010)γ′. Misfit dislocations and lattice strain fields existed at the α/γ′ interface for different habit planes; that is, (110)α∥(010)γ′ and (100)α∥(110)γ′ were analysed. EDAX (Energy dispersive X-ray) analysis showed that the composition of the γ-phase was approximately Ni4(Mo, Al, V); it contained 90° rotational domains of Ni3(Mo, Al, V) with a DO22 structure and Ni2(Mo, Al, V) with a Pt2Mo structure.