Mechanical behaviour of nanocomposites derived from zirconium based bulk amorphous alloys

摘要

The effects on mechanical properties of partial crystallization of a zirconium based bulk amorphous alloy (Vitl) are investigated. Nanocomposites are produced by appropriate heat treatments at temperatures higher than the glass transition temperature. Mechanical properties at room temperature are investigated by compression tests and hardness measurements including nanoindentation. The variation of the fracture stress with the degree of crystallinity is related to the nature, the size and the dispersion of the crystals in the amorphous phase. The variations of microstructure are estimated thanks to differential scanning calorimetry, X-ray diffraction and transmission electron microscopy. A significant connexion between crystals induces a decrease of the fracture stress whereas hardness continuously increases with crystallinity. From nanoindentation tests, Young's modulus and apparent yield stresses were roughly estimated and it is concluded that crystallization tends to increase the yield stress. Nevertheless, AFM observations of the imprints after indentation suggest that the mechanism of deformation can vary significantly with crystallization.