Interactions between high temperature deformation and crystallization in zirconium based bulk metallic glasses
Résumé
High temperature deformation of a ZrTiCuNiBe bulk metallic glass (BMG) is investigated by compression tests in the supercooled liquid region. When temperature is decreased or strain rate is increased, the amorphous alloy exhibits the usual Newtonian – non Newtonian behavior transition. Owing to appropriate heat treatments, partially crystallized alloys are produced, the associated microstructures are characterized and the volume fractions of crystal are measured. The interaction between high temperature deformation and crystallization is investigated by appropriate mechanical tests. According to the mechanical measurements, partial crystallization is responsible for an important increase of the flow stress and a promotion of the non-Newtonian behaviour. The deformation does not change significantly the volume fraction of crystal, the crystal composition neither the size. The flow stress increase with crystallization is analyzed under different hypotheses. It comes out that the flow stress increase can not be interpreted through a composition change in the residual amorphous matrix neither by the reinforcement due to hard crystallites nor by connections between crystals. It finally seems that the effect is rather due to the nanometric size of the crystals.
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