On the vibration-enhanced thermoplastic formability in bulk metallic glasses

Abstract

Bulk metallic glasses (BMGs) are a class of alloys highly suitable for the manufacturing of high-performance metallic components with intricate shapes for modern industries. However, how to achieve superior thermoplastic formability in BMGs is a most essential issue. In this work, vibration-enhanced thermoplastic formability was verified in 3 different types of BMGs (i.e. Pd40Cu30Ni10P20, Zr35Ti30Be26.75Cu8.25, and La55Al25Ni5Cu10Co5), suggesting that vibrational loading is a generic approach to assist the forming of BMGs. Under vibrational loading, the temperature-dependent viscosity of all the 3 BMGs was found to show more fragile behavior at higher vibration frequency. The structural relaxation spectroscopies of the 3 BMGs after vibrational loading suggest that the vibration-enhanced formability in BMGs might originate from a unified mechanism through which vibration modulates the hierarchical atomic dynamics of BMGs. Further inspections on fragility, structural factor, nanoindentation hardness, and relaxation enthalpy of the Pd40Cu30Ni10P20 BMG indicate that the free volume content increases at increasing vibration frequency. Aided by both experimental tests and molecular simulations, we argue that the vibration-enhanced formability in BMGs is because that vibrational loading increases the free volume content while reduces the size of flow units, and most importantly, homogenises the distribution of flow units.