Microstructure evolution of directionally solidified NiAl–28Cr–6Mo eutectic alloy under different withdrawal rates

The microstructure evolutions of directionally solidified NiAl–28Cr–6Mo eutectic alloy at withdrawal rates of 6–500 µm s⁻¹ and temperature gradients of 250 K cm⁻¹ were studied. The microstructure was composed of lamellar NiAl and Cr(Mo) phase, which had the crystallographic orientations of [111]NiAl∥[111]Cr(Mo) and (Formula presented.) NiAl∥ (Formula presented.) Cr(Mo) as well as the growth direction of <111>. With increasing withdrawal rate, the growth interface changed from planar to cellular and dendritic, the microstructure also transformed from planar eutectic to two-phase cellular eutectic and dendritic eutectic. The eutectic interlamellar spacing λ decreased according to the relationship of λ = 4.48V^−0.40, which indicated that the J–H model was applicable not only for the planar eutectic alloy but also for the cellular and dendritic eutectic alloys.