Kinetics of Structural Relaxation in Some Metallic Glasses

摘要

Amorphous metals or metallic glasses are metallic alloys in the solid statewithout (translational) long range order. When the obtained product is annealed at temperatures between 400 and 600 K atomic rearrangements in the amorphous state occur, which process is generally called structural relaxation. The thesis deals with the kinetics of structural relaxation in amorphous Fe40Ni40B20 and Pd40Ni40P20. In chapter 2 several models for the kinetics of structural relaxation are described, of which the most important is the mixed model. In this mixed model structural relaxation is considered to consist of two sub-processes: Chemical Short Range Ordering (CSRO) and Topological Short Range Ordering (TSRO). In chapter 3 the set-ups for the various experimental techniques which were used for the measurements (Young's modulus, electrical resistivity, Differential Scanning Calorimetry (DSC) and anelastic strain) are described. In chapter 4 a successful attempt to observe the transition from CSRO to TSRO is described. In chapter 5 the effect of defects on the kinetics of chemical ordering in, mainly, amorphous Fe40Ni40B20 has been studied. It is generally assumed that these defects control both diffusion and viscous flow. All experiments clearly show that the ordering kinetics slows down when the concentration of defects decreases. However, the rate is not controlled by flow defects, but by diffusion defects. In the last chapter, chapter 6, structural relaxation in amorphous Pd40Ni40P20 has been described in terms of the mixed model.