VISCOUS BEHAVIOR AND GLASS-FORMATION IN FE78B13SI9 AMORPHOUS ALLOY

Using a rotational viscometer, the viscosity of molten Fe78B13Si9 alloy was measured over the temperature range 1165-1350-degrees-C. The temperature dependence of the viscosity of liquid alloy is adequately described by the Arrhenius equation. However, this expression cannot be directly extended to the undercooled liquid temperature region. In this paper a proper equation derived from the free volume theory is proposed to describe the viscosity-temperature behaviour of Fe78B13Si9 alloy in the temperature range of the undercooled liquid and above its melting point. Furthermore, the isothermal time temperature-transformation curve for crystallization is constructed based on the assumption of homogeneous nucleation and crystal growth, together with the temperature dependence of the viscosity. The critical cooling rate required to form a glass of Fe78B13Si9 alloy was calculated to be approximately 10(5)-degrees-C s-1.