Zr-based Bulk Amorphous Alloys At Room Temperature Compression And Dynamic Characteristics

Bulk metallic glasses are a family of unique metastable materials and the earliest reports date back to the studies of Zr-based multi-component systems in the 1990's. The size limit in the formation of an amorphous solid thereafter has been broken through, and this opened a window for their applications as structural engineering materials. This, subsequently, has activated the research on their mechanical properties. Note that the Zr-based bulk metallic glasses manifest large forming abilities and thermal stabilities, in this thesis, we performed the studies on their mechanical properties. Zr65Al7.5Ni10Cu17.5 bulk metallic glass with 3mm in diameter were prepared by means of suction-casting method. The deformation and fracture behaviors under monaxial compression have been carried out on an Instron Univeral-Testing Machine at room temperature. We found: the samples experience elastic and plastic deformation processes before fracture, and the elastic strain is very large, it is about 2%. Shear bands along 45? angle with respect to the loading direction are observed in the cylinder of the deformed samples. The plastic deformation manifests a viscous flow behavior, and no work hardening is found during the plastic deformation process. Cracks form in the region where shear deformation is larger. As the plastic deformation accumulates in the origins of the cracks, fracture comes up and occurs in a very short time. The final fracture is mainly ascribed to the accumulation of the flow and the stress. To study the structure-property interrelation, the dynamical characteristics of storage modulus (G1), loss modulus (G1) and internal friction (G'/ G') of three Zr-Al-Ni bulk metallic glasses were examined by the method of DMA. These samples are electronic concentration (e/a)-constant phases and their show different dynamical mechanical behaviors at room temperature. Zr63Ni18 5Al18 5 alloy has the largest value of G' At the heat rate of 10C/min and the frequency of 5Hz, atomic relaxation occurs at about 300C in all the three samples. The peak temperature of G" and G"/ G' tends to elevated temperature with Zr concentration, while the intensity of the peaks showing a decreasing tendency. Combining the results with the XRD analysis, we pointed out that the onset temperature of crystallization locates at the starting point of the G' curve. The peak temperatures of G" and G"/ G' cannot be regarded as the onset temperature of crystallization. In addition, the variation tendency of G" and G"/ G' with respect to temperature, will provide information on the difference in local atomic structure of these e/a-constant bulk metallic glasses.