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

摘要

The microstructure evolutions of directionally solidified NiAl-28Cr-6Mo eutectic alloy at with-drawal rates of 6-500 mu m 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 parallel to[111]Cr(Mo) and NiAl parallel to 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 lambda decreased according to the relationship of lambda = 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.