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 electrom agnetic levitation technique. The crystal growth velocities were measu red as a function of undercooling using a high speed photosensing devi ce for time-resolved measurements of temperature during recalescence. The structures of the as-solidified samples were investigated by optic al microscopy and X-ray diffraction. The results of the growth velocit y measurements were analysed within current theories of dendrite growt h with special emphasis placed on non-equilibrium solidification due t o disorder trapping during rapid solidification of intermetallic phase s. The structure investigations in combination with growth velocity me asurements allow for a detailed analysis with respect to the identific ation of primary phases solidified in the different alloys.