Effect Of Shock Wave On ZrTiCuNiBe Bulk Metallic Glass

In order to prepare homogeneous bulk metallic glass (BMG), gravity-drivenberyllium transport in ZrTiCuNiBe melt and its influence on glass formation isinvestigated by a long time holding of metallic melts at above its liquidus temperature.The purpose of this dissertation is that investigating damage characteristics and fracturemechanism of Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5BMG impacted by high-speed projectiles,formation mechanism of the BMG by shock-wave quenching, and short-range orderstructure and crystallization kinetics and phase evolution using many experimental ways.Furthermore, another purpose of the dissertation is to reveal effects of shock wave onBMG.Damage characteristics and fracture mechanism of the BMG under planar shockwave and spherical wave are studied by scanning electron microscopy after impact ofhigh-speed projectiles fired by a two-stage light gas gun. Glass forming ability andformation mechanism of the BMG is investigated by shock-wave quenching of hightemperature and high pressure caused by high-speed impact. Thermal-elasticity propertiesof BMGs prepared by water quenching and shock-wave quenching are investigated byultrasonic and density measurements. Glass transition and crystallization kinetics,short-range order structure and crystallization process of the two BMGs are investigatedby differential scanning calorimetry, synchrotron radiation X-ray diffraction and hightemperature in situ X-ray diffraction, respectively. Pressure effects on crystallizationprocess and crystallization temperature of the two BMGs under high temperature and highpressure are also studied by in situ synchrotron radiation X-ray diffraction.The results show that the upper part of a quenched Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 bulk alloyrod contains more beryllium atoms and is amorphous. But the lower part with lessberyllium atoms contains crystalline phases. The composition gradient is possibly due tothe gravity-driven transport of Be-rich clusters and unmelted tiny solid pieces in the alloymelt. Under the impact of planar flyer, radial symmetric cracks form on the shockedsurface of the Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 BMG target. Shear cracks/bands about 35o to theshocking direction are found in the layer subjacent to the shocked surface. Evidences ofcrystallization and melting (liquid droplet-like pit) due to high strain rate deformation arealso observed inside adiabatic shear cracks/bands. Under the impact of sphericalprojectiles, crater profiles and lamination cracks are presented in addition to the adiabaticshear cracks/bands. Under compressive or tensile stress, cracking of the BMG follows aprocess of nucleation, growth, and coalescence of micro-voids in shear bands, which werepossibly initiated by release and coalescence of excess free volumes. Compared withwater-quenched Zr41Ti14Cu12.5Ni10Be22.5 BMG, shock-wave-quenched BMG exhibitshigher glass transition temperature, crystallization temperature, crystallization peaktemperature, thermal stability, and bigger acoustic velocities and lower density.Shock-wave-quenched BMG has higher coordination numbers in the range of r 2.4-5.6? and lower numbers in the range of r ⁵.6-9.5 ? than those for a water-quenched one.The first coordination number, N=14.4 and 14.0, is estimated from a distance of 2.1-3.7 ?for shock-wave-quenched sample and water-quenched one, respectively. Undercontinuous heating conditions, shock-wave-quenched BMG possesses different phasesand different precipitation sequences form those for water-quenched and shock wavetreated ones, respectively. The differences in crystallization are probably attributed todifferent atomic configurations between the three BMGs treated by different ways. Atdifferent pressures, the BMGs prepared by shock-wave quenching and water quenchingexhibit the same primarily precipitated phase, yet the following crystallization sequencesare different. The onset temperature of crystallization is found to increase with pressurefor the two BMGs, but with a sudden drop at about 5.6 and 6.0 GPa for water-quenchedBMG and shock-wave-quenched one respectively, which correspond to differentcrystallization sequence at about 5.6 and 6.0 GPa in comparison with those at otherpressures for water-quenched BMG and shock-wave-quenched ones. These may beattributed to that the BMGs possess different atomic configurations at different pressures.