GLASS-FORMATION IN BINARY AND TERNARY ZR BASED FE AND NI BEARING ALLOYS

Rapid solidification of the Zr76Fe24-xNix alloys (x = 0, 4, 8, 12, 16, 20 and 24) by melt spinning under different conditions has yielded fu lly amorphous as well as partially crystalline ribbons. The partially crystalline ribbons have been found to contain crystal aggregates comp rising a core of the beta-Zr phase surrounded by peripheral crystals o f the Zr-3(Fe,Ni) phase in alloys with x < 12. In alloys containing la rger amount of Ni (x greater than or equal to 12), both Zr3Ni and Zr-3 (Fe,Ni) crystals have been found to be present in the periphery. The nucleation of the core crystals and the peripheral crystals in the und ercooled melt has been examined by considering transient and steady st ate homogeneous and heterogeneous nucleation. The transient nucleation time and the steady state nucleation rate of crystals have been evalu ated. For this purpose, use has been made of molar free energy differe nce Delta G(c) between the liquid and the crystalline phases determine d from experimentally evaluated quantities. The growth of the crystals in the undercooled melt has been examined taking into account recales cence and heat removal during melt spinning. The glass forming ability of the alloys has been evaluated on the basis of the avoidance of cry stallization approach. A comparison has been made between the microstr uctures of the splat cooled and the melt spun alloys in order to under stand the process of solidification and the nature of phase transforma tion during post solidification cooling.