Glass formation in binary and ternary Zr based Fe and Ni bearing alloys

Abstract

Rapid solidification of the Zr₇₆Fe_24-xNi_x alloys (x = 8, 12, 16, 20 and 24) by melt spinning under different conditions has yielded fully amorphous as well as partially crystalline ribbons. The partially crystalline ribbons have been found to contain crystal aggregates comprising a core of the β-Zr phase surrounded by peripheral crystals of the Zr₃(Fe,Ni) phase in alloys with x < 12. In alloys containing larger amount of Ni (x ≥ 12), both Zr₂Ni and Zr₃(Fe,Ni) crystals have been found to be present in the periphery. The nucleation of the core crystals and the peripheral crystals in the undercooled melt has been examined by considering transient and steady state homogeneous and heterogeneous nucleation. The transient nucleation time and the steady state nucleation rate of crystals have been evaluated. For this purpose, use has been made of molar free energy difference ΔG_c between the liquid and the crystalline phases determined from experimentally evaluated quantities. The growth of the crystals in the undercooled melt has been examined taking into account recalescence and heat removal during melt spinning. The glass forming ability of the alloys has been evaluated on the basis of the avoidance of crystallization approach. A comparison has been made between the microstructures of the splat cooled and the melt spun alloys in order to understand the process of solidification and the nature of phase transformation during post solidification cooling.