The limited annealing treatment of the Zr55Cu30Al10Ni5 metallic glass below its glass transition temperature

Abstract

Annealing treatment below the glass transition temperature of Zr55Cu30Al10Ni5 bulk metallic glass (BMG) specimens are investigated. Every 10K temperature interval isothermal limited annealing treatment time will be selected to draw up time–temperature–transformation (T–T–T) curve. The apparent activation energy of crystallization is about 325±7kJ/mol, higher than the values of supercooled liquid region conditions. Surface hardness of the samples before and after the limited annealing treatment are tested by nanoindentation, where the spherical-like crystallization morphology indicate the higher standard deviation of surface hardness of the BMG after the limited annealing treatment. The crystallization kinetics of the Avrami exponent is 4 in accordance with spherical-like crystallization morphology. A short review on mathematical setting of the problem could distinctly give the differences of the different crystallization behaviors at different temperature regions. Avrami exponent is from 4 to 3, explaining the crystallization morphology is from spherical-like to dendritic, could be ascribed to the concepts of symmetry breaking.