CRYSTALLIZATION OF NI78B14SI8 STUDIED BY ADIABATIC CALORIMETRY - THERMODYNAMIC AND KINETIC ASPECTS

Thermodynamic and kinetic aspects of the crystallization of an Ni78B14Si8 metallic glass have been investigated by adiabatic calorimetry. The results are analyzed on the basis of a multiple-stage devitrification mechanism proposed to consist of (i) structural relaxation at low temperatures, (ii) primary crystallization of a nickel-silicon solid solution, (iii) formation of a fully crystalline but metastable mixture, and (iv) slow reactions in the fully crystalline phase which finally produces the stable three-phase mixture. A thermodynamic approach for rationalization and prediction of crystallization sequences is discussed. The heat capacities and thermodynamic properties for amorphous and crystallized (1/100)Ni78B14Si8 are reported. The difference in enthalpy of formation at 298.15 K between the quenched and annealed glass, and the annealed glass and a metastable crystalline mixture is 830 J mol-1 and 5470 J mol-1, respectively.