Encapsulated Zr-based bulk metallic glass with large plasticity

Copper (Cu) coatings were electroplated onto Zr57Al10Ni8Cu20Ti5 bulk metallic glass (BMG) in three different ways; laterally coated, two ends coated, and completely wrapped/encapsulated. The mechanical behavior of these three different types of specimen were investigated. The results show that, as compared to the poor ductility (∼2%) of the uncoated specimen, the side surface coated specimen exhibits a higher ductility of around 6.5% plastic strain before failure, under the effect of the lateral confinement by the Cu coating. Thanks to the elimination of friction between the platens and the specimen, the two ends coated specimen further demonstrates a larger plasticity of ∼13%. Most interestingly, the largest plastic strain of ∼20% was obtained in the completely encapsulated specimen. This drastic increase in plasticity is believed to originate from the changes of the frictional boundary conditions, the lateral confining stress and the deformation induced heterogeneous microstructure.