RAPID SOLIDIFICATION OF UNDERCOOLED NICKEL-ALUMINUM MELTS

Melts of Ni100-xAlx of different compositions (x = 20.2, 25, 26.25 and 30.8) were undercooled up to 250 K by the application of the electromagnetic levitation technique. The crystal growth velocities were measured as a function of undercooling using a high speed photosensing device for time-resolved measurements of temperature during recalescence. The structures of the as-solidified samples were investigated by optical microscopy and X-ray diffraction. The results of the growth velocity measurements were analysed within current theories of dendrite growth with special emphasis placed on non-equilibrium solidification due to disorder trapping during rapid solidification of intermetallic phases. The structure investigations in combination with growth velocity measurements allow for a detailed analysis with respect to the identification of primary phases solidified in the different alloys.