Nucleation and growth in surface-melted crystalline and amorphous Fe40Ni40P14B6 alloys

The well-known glass-forming alloy Fe40Ni40P14B6 was surface melted by an electron beam traversing its surface at various velocities in an identical manner for both the crystalline and the amorphous state of the alloy. Cross-sectional optical metallography and numerical heat-flow analysis were used to show that (1) crystallization of the amorphous state does not occur during treatment around or in the regrown layer at the highest processing speeds, a behavior consistent with an extrapolation of isothermal nucleation and growth measurements; (2) initial resolidification of the molten layer is always crystalline when the melt pool contacts underlying crystalline material where nucleation is immediate; and (3) solidification front velocities greater than 5 +/- 0. 5 cm/s exceed the maximum kinetic limit for growth of the crystalline phase and amorphous layers are formed, a result consistent with the eutectic nature of the alloy. Inconsistencies with the work of previous investigators of this system are discussed.